Content uploaded by Sébastien Lavoué
Author content
All content in this area was uploaded by Sébastien Lavoué
Content may be subject to copyright.
Accepted by J. Friel: 9 Jul. 2010; published: 1 Sep. 2010
1
ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN
1175-5334 (online edition)
Copyright © 2010 · Magnolia Press
Zootaxa 2600: 1–52 (2010)
www.mapress.com
/zootaxa/
Article
African weakly electric fishes of the genus Petrocephalus (Osteoglossomorpha:
Mormyridae) of Odzala National Park, Republic of the Congo (Lékoli River,
Congo River basin) with description of five new species
SÉBASTIEN LAVOUÉ
1
, JOHN P. SULLIVAN
2
& MATTHEW E. ARNEGARD
3
1
Department of Zoology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK. E-mail: s.lavoue@nhm.ac.uk
2
Cornell University Museum of Vertebrates, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA. E-mail: js151@cornell.edu
3
Human Biology Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N., Seattle, WA 98109, USA. E-mail:
arnegard@zoology.ubc.ca
Table of contents
Abstract ...............................................................................................................................................................................2
Résumé................................................................................................................................................................................ 2
Introduction .........................................................................................................................................................................2
Material and methods ..........................................................................................................................................................4
Result................................................................................................................................................................................... 6
List of Petrocephalus species of Odzala............................................................................................................................. 6
Petrocephalus binotatus Pellegrin, 1924..................................................................................................................... 6
Petrocephalus zakoni n. sp.......................................................................................................................................... 9
Petrocephalus valentini n. sp. ...................................................................................................................................13
Petrocephalus balayi Sauvage, 1883......................................................................................................................... 16
Petrocephalus microphthalmus Pellegrin, 1908 ........................................................................................................19
Petrocephalus odzalaensis n. sp. ...............................................................................................................................22
Petrocephalus christyi Boulenger, 1920 ....................................................................................................................25
Petrocephalus sauvagii (Boulenger, 1887)................................................................................................................ 29
Petrocephalus pulsivertens n. sp. ..............................................................................................................................32
Petrocephalus grandoculis Boulenger, 1920............................................................................................................. 35
Petrocephalus mbossou n. sp. ...................................................................................................................................38
Discussion .........................................................................................................................................................................41
Additional taxonomic remarks ..........................................................................................................................................43
Comments on the identification of Petrocephalus in the Congo and Lower Guinea provinces .......................................44
Key to the Petrocephalus species of Odzala .....................................................................................................................45
Acknowledgments .............................................................................................................................................................46
References......................................................................................................................................................................... 46
Additional material examined ..........................................................................................................................................49
Comparative type material examined.................................................................................................................................51
LAVOUÉ ET AL.2 · Zootaxa 2600 © 2010 Magnolia Press
Abstract
Here we examine new collections of Petrocephalus species (Osteoglossomorpha: Mormyridae: Petrocephalinae) made
within Odzala National Park in the
Republic of the Congo (Lékoli River drainage, northwestern Congo River basin). We
compare these collections to type material of all nominal Petrocephalus species described from the Congo basin and the
adjacent Lower Guinea ichthyofaunal province. Based on morphology and electric signal characteristics we recognize
eleven distinct species of Petrocephalus in these collections, including five new species described herein: Petrocephalus
binotatus, Petrocephalus zakoni n. sp., Petrocephalus valentini n. sp., Petrocephalus balayi, Petrocephalus
microphthalmus, Petrocephalus odzalaensis n. sp., Petrocephalus christyi, Petrocephalus sauvagii, Petrocephalus
pulsivertens n. sp., Petrocephalus grandoculis and Petrocephalus mbossou n. sp. Each species can be distinguished by a
combination of characters, the most important of which are numbers of dorsal and anal fin rays, mouth width, eye size,
number of upper jaw teeth and melanin markings. Electric signal waveform characteristics are useful for diagnosing a
few of the species. The eleven Petrocephalus species of the Odzala assemblage appear to be reproductively isolated
biological species based on genetic evidence we have gathered from the mitochondrial cytochrome b gene. Our study of
Petrocephalus type material reveals that Petrocephalus guttatus was erroneously assigned to this genus; we now assign
this species to Pollimyrus within the sister subfamily, Mormyrinae. Additionally, we provide a dichotomous key to the
eleven Petrocephalus species of Odzala National Park.
Key words: Petrocephalinae, electric fish, electric organ discharge, Central Africa, phylogeny, cytochrome b, integrative
taxonomy
Résumé
Nous avons récemment réalisé d’importantes collections ichtyologiques de la rivière Lékoli (basin du fleuve Congo) qui
draine la partie sud du Parc National d’Odzala (République du Congo), comprenant en particulier de nombreux
spécimens de poissons électriques de la famille des Mormyridae. Ici nous avons étudié les Petrocephalus
(Petrocephalinae, Mormyridae, Osteoglossomorpha) que nous avons comparé au matériel type de toutes les espèces
décrites du bassin du Congo et de la région de la Basse Guinée. L’examen de la morphologie externe nous a permis
d’identifier 11 espèces de Petrocephalus à Odzala–dont cinq d’entre elles sont nouvelles et décrites ici–: Petrocephalus
binotatus, Petrocephalus zakoni n. sp., Petrocephalus valentini n. sp., Petrocephalus balayi, Petrocephalus
microphthalmus, Petrocephalus odzalaensis n. sp., Petrocephalus christyi, Petrocephalus sauvagii, Petrocephalus
pulsivertens n. sp., Petrocephalus grandoculis et Petrocephalus mbossou n. sp. Chacune de ces espèces se distingue des
autres par une combinaison unique de plusieurs caractères dont les plus importants sont les nombres de rayons aux
nageoires dorsales et anales, la largeur de la bouche, le diamètre de l’œil, le nombre de dents sur la mâchoire supérieure
et le patron de pigmentation. La forme des décharges électriques ne permet en pratique que de distinguer quelques
espèces. Ces 11 espèces de Petrocephalus à Odzala semblent être génétiquement isolées les unes des autres comme le
montre une analyse phylogénétique fondée sur la comparaison du gène du cytochrome b. Parmi les autres espèces
nominales de Petrocephalus du Congo et de la Basse Guinée, nous avons constaté que Petrocephalus guttatus n’est pas
un Petrocephalus. Nous le réassignons au genre Pollimyrus de la sous-famille des Mormyrinae. Enfin, nous proposons
une clé d’identification dichotomique des 11 espèces de Petrocephalus présentement connues à Odzala.
Introduction
Petrocephalus Marcusen, 1854 is the sole genus within the African weakly electric fish subfamily
Petrocephalinae (Osteoglossomorpha: Mormyridae). This genus currently includes 25 valid species
(Eschmeyer & Fricke, 2010) that are distributed across tropical and subtropical freshwater regions of Africa.
Morphological (Taverne, 1969) and molecular evidence (Lavoué et al., 2000; Sullivan et al., 2000) support
the monophyly of Petrocephalus and its sister relationship to all remaining Mormyridae (subfamily
Mormyrinae). Identification of different Petrocephalus species is often difficult due to subtle morphological
differentiation between many species. Like other mormyrids, Petrocephalus species produce weak electric
pulses from an electric organ in the caudal peduncle for the purposes of object detection, orientation and
communication (Bennett, 1970; Lissmann, 1958; Moller, 1995). While in other mormyrid genera electric
organ discharge (EOD) waveforms often differ substantially among species and are useful taxonomic
markers, EOD waveforms of Petrocephalus are relatively conserved across the genus. The typical EOD
Zootaxa 2600 © 2010 Magnolia Press · 3
PETROCEPHALUS OF ODZALA
waveform of Petrocephalus is short in duration and exhibits two main phases of alternating polarity, the first
of which is head-positive (Bass, 1986; Sullivan et al., 2000). Often, one or two additional phases of much
smaller relative amplitude are present in the EOD (Lavoué et al., 2008). All Petrocephalus species examined
to date have electric organs composed of simple "NPp"-type electrocytes with non-penetrating stalks
innervated on the posterior side of each electrocyte (Bass, 1986).
FIGURE 1. Map of Africa (right) showing the entire Congo River and its main tributaries together with the neighboring
Lower Guinea province (first inset at center). The boundary between the Congo and Lower Guinea provinces is shown
by a dashed line. Filled black circles indicate type localities for all Petrocephalus species that were described from either
province and were considered valid just prior to the present study. Exact type localities are unknown for P. balayi and P.
sauvagii. Based on our understanding of the chronology of Central African exploration at the time of the descriptions, we
estimate these type localities to be the following: the vicinity of Pool Malebo on the Lower Congo River near the modern
cities of Brazzaville and Kinshasa [4.25° S, 15.29° E] for P. sauvagii; and the vicinity of the present-day city Lambaréné
on the Lower Ogooué River [0.7° S, 10.22° E] for P. balayi. Second inset at the far left: detailed map of Odzala National
Park, located in the Congo River basin. Within the boundaries of the park, forest is shown in green and savannah in
yellow. The red oval indicates our collection area (a segment of the Lékoli drainage system, including the lower parts of
two of its tributaries, the Pandaka and Lékénie Rivers).
Despite the apparent conservatism in morphology and EOD waveforms among Petrocephalus, a high
degree of genetic variation has been noted within nominal species, suggesting the presence of cryptic species
LAVOUÉ ET AL.4 · Zootaxa 2600 © 2010 Magnolia Press
diversity (Agnèse & Bigorne, 1992; Lavoué et al., 2008; van der Bank, 1996). This suspicion was confirmed
by the results of two recent collecting trips to Odzala National Park,
Republic of the Congo, in the
northwestern part of the Congo River basin (Fig. 1). Combining morphological data, EOD recordings and
genetic evidence, Lavoué et al. (2008) identified eleven species of Petrocephalus from these Odzala
collections. In the present taxonomic study of Odzala specimens, we now provide morphological diagnoses
and descriptions for each of the eleven species, five of which are new. When useful, EOD characteristics are
included in our diagnoses. We also expand a cytochrome b-based molecular phylogeny, which presently
includes 17 species and 59 specimens of Petrocephalus, as an independent genetic test of the distinctiveness
of these taxa.
Material and methods
Specimen sampling. We collected numerous Petrocephalus specimens during two recent trips to Odzala
National Park,
Republic of the Congo, in August 2002 and June 2006 (Fig. 1). Comparative material came
from several localities in Gabon (Lavoué et al., 2004), the Dzangha Sangha Reserve (Sangha River, Central
African Republic, northwestern Congo basin) and the Lower Congo River in the vicinity of Pool Malebo
(
Republic of the Congo). We also examined type material (at least part of the type series) for all previously
described species from the Congo basin and the Lower Guinea province. We included Lower Guinean species
in our comparisons because this region shares faunistic affinities with the Congo River basin (Roberts, 1975).
Our molecular analyses (see below) included representatives of the eleven Petrocephalus species from Odzala
along with representatives of three species from Lower Guinea and additional species from West and East
Africa.
In the list of material examined, we indicate the capacity in which each specimen was used as follows:
morpho (morphological examination), EOD (analysis of the electric organ discharge), and DNA (cytochrome
b sequencing).
Morphology. Methods for making counts and measurements follow those of Lavoué et al. (2004). We
made 20 measurements on each specimen using a digital caliper with a precision of ± 0.1 mm. Abbreviations
and definitions for each of these measurements follow those given by Boden et al. (1997) with the exception
of standard length (SL), mouth position (MP) and mouth width (MW), which follow the definitions of Lavoué
et al. (2004). We also made seven meristic counts on each specimen: number of branched dorsal fin rays,
excluding all unbranched rays (DR); number of branched anal fin rays, excluding all unbranched rays (AR);
number of pored scales along the lateral line (SLL); number of scales around the caudal peduncle (ScP);
number of scales between the origin of the anal fin and the lateral line, excluding the pored scale itself (SDL);
and number of teeth on the lower and upper jaws (TLJ and TUJ, respectively). The number of scales around
the caudal peduncle was found not to vary among species (see Descriptions), so this meristic is not reported in
Tables 1–10.
We categorized the sex of each specimen into one of two categories—obvious males or all other
individuals—by checking the body profile of each preserved specimen along the base of the anal fin. A
strongly indented (versus straight) anal fin base is exhibited only by sexually mature males (Pezzanite &
Moller, 1998).
We investigated the distribution pattern of Knollenorgan-type electroreceptors on the head of
Petrocephalus specimens. Harder (1968) described three dense clusters of Knollenorgans, which he called the
"Augenrosette," "Nackenrosette" and "Kehlrosette," on the heads of some Petrocephalus species (Fig. 2).
When present, the "Augenrosettes" are situated above the anterior half of the left and right eyes; the
"Nackenrosettes" are dorsally situated on each side of the nape, slightly anterior to the opercular openings;
and the "Kehlrosettes" are situated anterior to the insertion of the pectoral fins, with part of the rosette
extending slightly ventrally from the pectoral fin insertion.
EOD waveforms and electric organ anatomy. In a companion paper to the present work (Lavoué et al.,
2008) we provided an in-depth analysis and description of EOD waveform variation among the Petrocephalus
of Odzala, as well as a discussion of its evolutionary significance. Methods for recording EODs and
Zootaxa 2600 © 2010 Magnolia Press · 5
PETROCEPHALUS OF ODZALA
quantifying EOD waveform variation are described therein. Here, we summarize only the most salient
features of EOD variation among Odzala’s Petrocephalus species. The EOD recordings we illustrate are raw
traces, uncorrected for temperature differences. Details on fine-scale EOD variation not relevant to species
diagnosis are given in the companion paper, which also describes our methods for electric organ histology.
Our nomenclature for describing electrocyte anatomy follows Bass (1986), Alves-Gomes and Hopkins (1997)
and Sullivan et al. (2000).
FIGURE 2. Knollenorgan rosettes depicted on a schematic drawing of the head of a specimen of Petrocephalus
pulsivertens n. sp. Dense clusters of Knollenorgan electroreceptors on the heads of this and several other Petrocephalus
species were described by Harder (1968) as the "Augenrosette," "Nackenrosette" and "Kehlrosette," depending on their
position on the head. Each black point represents a single Knollenorgan electroreceptor. Several isolated Knollenorgans
occur outside these three rosettes (in this individual of P. pulsivertens), but they are not indicated in the drawing for
clarity.
DNA sequencing and molecular phylogenetic methods. We expanded the cytochrome b (cytb) dataset
published in Lavoué et al. (2008) by adding sequences for two new taxa: Petrocephalus bovei (Valenciennes
in Cuvier and Valenciennes, 1847) from the Baro River at Gambela, Ethiopia (White Nile basin, CU 94594
[two specimens examined]) and Petrocephalus catostoma (Günther, 1866) from the Rufiji River, Tanzania
(CU 93895 [one specimen examined]) and from the Wani River, Tanzania (CU 93893 [two specimens
examined] and CU 93894 [one specimen examined]). This comparative material is important because it is
common for specimens from the Congo basin to be identified as P. catostoma in collections, and P. bovei has
a widespread distribution to the north of the Congo basin. To root the phylogenetic trees we used Myomyrus
macrops Boulenger 1914, Mormyrops nigricans Boulenger, 1899, and Gnathonemus petersii (Günther, 1862)
as outgroups.
DNA was extracted from 90% ethanol-preserved fin clips or dorsal muscle. PCR amplification and
sequencing of the complete cytb gene (1,140 base pairs) were as described by Sullivan et al (2000) using the
primers designed by Lavoué et al (2008). Cytb sequences generated in this study have been deposited to
Genbank under accession numbers GU982921 to GU982926.
New cytb sequences were aligned by eye with previous sequences using PAUP* ver. 4.1.10 (Sinauer
Associates, Inc.). Alignment was trivial without any insertions or deletions. We inferred phylogenetic trees for
two different character matrices using maximum likelihood (ML). The first matrix (dataset #1; 1,140
nucleotide positions) included all positions and types of substitution. The second matrix (dataset #2) was the
same as the first, except that fast evolving transitions at third codon positions were ignored by replacing third
codon position guanines (G) and cytosines (C) with adenines (A) and thymines (T), respectively (Phillips et
al., 2004).
LAVOUÉ ET AL.6 · Zootaxa 2600 © 2010 Magnolia Press
Maximum likelihood (ML) trees and the robustness of the internal branches of the best ML tree topologies
(one topology for each data matrix) were simultaneously inferred using the program RAxML 7.0.4
(Stamatakis, 2006). We performed bootstrap searches (1,000 replicates) and heuristic phylogenetic searches
under the general time reversible model of nucleotide substitution with rate heterogeneity following a discrete
gamma distribution (GTR+
). We did so using the GTRGAMMA option in RAxML (consult the second part
of section 5.1 in the RAxML 7.0.4 Manual for details).
Results
List of Petrocephalus species of Odzala
Petrocephalus binotatus Pellegrin, 1924
Petrocephalus binotatus Pellegrin (1924): 1.
[Odzala field identification: Petrocephalus sp. 1, OTU 1]
Images. Fig. 3A, photo of a live specimen from Odzala, Fig. 3B, photo of a preserved specimen from Odzala
and Fig. 14, drawing of the holotype (MRAC 15191) from Pellegrin (1928), p. 12. Photo of the holotype in
Harder (2000).
Type material. Holotype, MRAC 15191 [examined], sex undet., 83.2 mm SL. Democratic Republic of
the Congo
, Congo River at Ikengo [estimated geographic coordinates: 0.13° S, 18.13° E], H. Schouteden coll.
Other specimens. We have examined 35 additional specimens from Odzala National Park (see
"additional material examined").
Diagnosis. The following diagnosis is based on all examined specimens of P. binotatus, regardless their
geographic origins. Petrocephalus binotatus is distinguished from all other Petrocephalus species from Lower
Guinea and Congo provinces by the following combination of characteristics. Dorsal fin shorter than the anal
fin (1.5
AFL/DFL, range = 1.5–1.7). Dorsal fin with at least 20 branched rays (range = 20–24). Anal fin
with at least 30 branched rays (range = 30–33). Sixteen teeth or fewer (range = 8–16) in the upper jaw, 24
teeth or fewer (range = 19–24) in the lower jaw. Eye relatively large (HL/ED
4.0, range = 3.5–4.0). Mouth
sub-terminal; ratio of head length to mouth position (HL/MP) between 3.9 and 6.1. Unique pigmentation
pattern with the presence of three well defined black patches: (1) a distinct (although sometimes covering only
few scales), more or less round/oval, black mark situated slightly anterior to the dorsal fin on each side of the
body; (2) a black mark at the base of each pectoral fin; (3) an ovoid black mark centered at the base of the
caudal fin that does not extend onto the upper and lower fleshy lobes of this fin. EOD of normal polarity (i.e.,
first major phase head-positive).
Description. This description corresponds to the Odzala material (e.g., ranges, averages, medians), except
where explicit reference is made to the holotype (from Ikengo). Morphometric ratios and meristic data for
non-type specimens from Odzala and the holotype are presented in Table 1. Petrocephalus binotatus,
described by Pellegrin (1924), is a small sized species within the genus Petrocephalus (maximum SL
observed in Odzala = 88.4 mm, holotype = 83.2 mm). Body ovoid, longer than high (2.3
SL/H 2.8,
average = 2.5, holotype = 2.4) and laterally compressed. Head length of Odzala specimens between 3.7 and
4.0 times in standard length (average = 3.9, holotype = 3.6). Snout short (6.8
HL/SNL 8.3, average = 7.8,
holotype = 5.5) and round. Eye large (3.5
HL/ED 4.0, average = 3.6, holotype = 3.6). Mouth small (4.4
HL/MW
5.2, average = 4.7, holotype = 3.2), sub-terminal, opening under the anterior half of the eye. Teeth
small and bicuspid, 8 to 16 (median = 10) in a single row in the upper jaw, 19 to 24 (median = 21) in the lower
jaw. Dorsal and anal fins originate in the posterior half of the body (1.5
SL/PDD 1.6) and (1.6 SL/PAD
1.7), respectively. Pre-dorsal distance slightly greater than the pre-anal distance (1.0 < PDD/PAD 1.1).
Dorsal fin with 20–22 branched rays (median = 21, holotype = 24). Anal fin with 30–33 branched rays
(median = 32, holotype = 33). Scales cover the body, except for the head. Lateral line visible and complete
with 37 or 38 pored scales along its length. Eleven to 13 scales (median = 12), between the anterior base of the
Zootaxa 2600 © 2010 Magnolia Press · 7
PETROCEPHALUS OF ODZALA
anal fin and the lateral line. Caudal peduncle thin (1.8 CPL/CPD 2.2, average = 2.0, holotype = 2.3).
Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation.
Three distinct rosettes of Knollenorgans are present on the head (Augenrosette, Nackenrosette and
Kehlrosette).
FIGURE 3. Petrocephalus binotatus of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale: the photo has been maximally enlarged to better illustrate details of body shape,
melanin patterning, etc.). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD waveforms displayed
separately for obvious males and other individuals (see text). One EOD was arbitrarily selected from each recorded
individual and superimposed with the other recordings (N = number of individuals, given separately for obvious males
and all other individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up)
on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).
LAVOUÉ ET AL.8 · Zootaxa 2600 © 2010 Magnolia Press
TABLE 1. Principal morphometric ratios and meristic counts for the holotype (MRAC 15191) and seven specimens
from Odzala (CU 88063, CU 88079, CU 88076, CU 88074, CU 87838, CU 88041, CU 88091) of Petrocephalus
binotatus (Abbreviations: m= male; Std
–Dev= standard deviation; Min–Max= minimum–maximum).
Live coloration (Fig. 3A). Body uniformly white-silver, with the presence of three characteristic melanin
marks on each side of the body: (1) a distinct, approximately round/oval black mark situated slightly anterior
to the dorsal fin, sometimes covering only a few scales; (2) a black spot at the base of the pectoral fin; (3) an
ovoid black mark centered at the base of the caudal fin that does not extend onto the upper and lower parts of
the caudal fin. Fins translucent.
Distribution (Fig. 1). Apparently endemic to the Congo River basin. Holotype from the locality Ikengo
on the Congo River just below Mbandaka. One of the most abundant Petrocephalus species in Odzala. We
collected P. binotatus at several localities along the main channel of the Lékoli River. At the time of our
Holotype (m) Specimens from Odzala (n=7)
Min–Max Mean Std–Dev
Standard length (mm) 83.2 65.0–88.4 76.0 8.1
Head length (mm) 23.1 17.3–21.9 19.6 1.6
Ratio of standard length (SL):
SL/body height (H) 2.4 2.3–2.8 2.5 0.2
SL/head length (HL) 3.6 3.7–4.0 3.9 0.1
SL/pre-dorsal distance (PDD) 1.6 1.5–1.6 1.6 0.0
SL/pre-anal distance (PAD) 1.7 1.6–1.7 1.7 0.0
SL/dorsal fin length (DFL) 4.5 4.2–4.9 4.7 0.3
SL/anal fin length (AFL) 2.8 2.8–3.3 3.0 0.2
SL/caudal peduncle length (CPL) 7.0 6.5–7.6 7.1 0.4
SL/mouth width (MW) 11.6 17.3–18.2 20.3 1.0
Ratio of head length (HL):
HL/snout length (SNL) 5.5 6.8–8.3 7.8 0.5
HL/mouth width (MW) 3.2 4.4–5.2 4.7 0.3
HL/eye diameter (ED) 3.6 3.5–4.0 3.6 0.2
HL/interorbital width (IOW) 2.3 2.6–3.0 2.8 0.2
HL/head width (HW) 1.9 1.8–1.9 1.8 0.0
HL/mouth position (MP) 3.9 4.4–6.1 5.1 0.6
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.3 1.8–2.2 2.0 0.2
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 24 20–22 21
Anal fin branched rays (AR) 33 30–33 32
Number of scales in the lateral line (SLL) 37 37–38 37
Number of scale rows between the anterior base of the anal
fin and the lateral line (SDL)
11 11–13 12
Number of teeth in the upper jaw (TUJ) 8–16 10
Number of teeth in the lower jaw (TLJ) 19–24 21
Zootaxa 2600 © 2010 Magnolia Press · 9
PETROCEPHALUS OF ODZALA
collections, however, this species appeared to be absent from small tributary creeks flowing through the forest
or savannah.
Petrocephalus binotatus was absent in two recent collections from the Lower Congo River made in the
vicinities of the Pool Malebo (one collection by M. Stiassny and B. Schelly in 2002, housed in the American
Museum of Natural History; the other by P. Feulner and F. Kirschbaum in 2006, housed in the Leibniz
Institute of Freshwater Ecology and Inland Fisheries, Berlin; pers. obs. of material contained in these
collections).
Electric organ discharge (Fig. 3C). Petrocephalus binotatus males and females produce EODs with
overall waveforms that are typical for the genus, being similar to EODs produced by many other congeners.
However, this is one of the few Petrocephalus species (e.g., the only Petrocephalus species in Odzala
National Park) for which possible EOD sex differences have been detected thus far in field recordings. As
with other Petrocephalus species exhibiting possible sex differences, magnitudes of the differences between
males and females are small. In Odzala, for example, mean EOD duration (± std. dev.) is 0.330 ± 0.074 msec
in obvious adult males and 0.270 ± 0.033 msec in other adult and sub-adult individuals, based on 1.5%
voltage deviations from baseline relative to peak-peak amplitude. Statistics for waveform landmarks and other
EOD measurements are provided by Lavoué et al. (2008) for specimens recorded in Odzala National Park. No
EOD recordings are available for the holotype or other specimens collected near the type locality (Ikengo,
Congo River, Fig. 1). Electrocytes are assumed to be of type NPp based on characteristics of the EOD,
although electrocyte anatomy has not yet been confirmed histologically.
Remarks. Specimens of P. binotatus from Odzala resemble the holotype described from the main channel
of the Congo River (locality Ikengo, Fig. 1) (Pellegrin, 1924). However, they also exhibit several differences,
mainly in head morphology. The holotype has a larger mouth (HL/MW = 3.2 versus
4.4 in Odzala
specimens), a longer snout (HL/SNL = 5.5 versus
6.8 in Odzala specimens) and a larger interorbital width
(HL/IOW = 2.3 versus
2.6 in Odzala specimens). Additional comparative material from the type locality
and other localities in the Congo basin are necessary to determine the taxonomic implications of these
differences.
Petrocephalus zakoni n. sp.
[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 2, OTU 2]
Images. Fig. 4A, photo of a live specimen from Odzala and Fig. 4B, photo of the preserved holotype (CU
88101).
Type material. Holotype, CU 88101 (morpho, EOD), male, 86.0 mm SL. Republic of the Congo, small
channel around island in Lékoli River (Congo basin), Odzala National Park, (0.62° N, 14.95° E). J.P. Friel, S.
Lavoué & J.P. Sullivan coll., 20 August 2002.
Paratypes. CU 88036 (morpho, EOD), sex undet., 81.4 mm SL; CU 88042 (morpho, EOD), male, 78.6
mm SL; CU 88037 (morpho, EOD), sex undet., 79.6 mm SL; CU 88077 (morpho), male, 84.8 mm SL.
Republic of the Congo, Pandaka River (Congo basin), Odzala National Park, (0.62° N, 14.92° E), J.P. Friel, S.
Lavoué & J.P. Sullivan coll., August 2002. CU 88104 (morpho, EOD), sex undet., 83.5 mm SL; AMNH
251426 (ex CU 88100) (morpho, EOD), male, 73.7 mm SL; AMNH 251427 (ex CU 88103) (morpho, EOD),
sex undet., 77.2 mm SL.
Republic of the Congo, small channel around island in Lékoli River (Congo basin),
Odzala National Park (0.62° N, 14.95° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002. CU 88093
(morpho, EOD), male, 67.4 mm SL; AMNH 251424 (ex CU 88088) (morpho, EOD), sex undet., 75.8 mm SL;
AMNH 251425 (ex CU 88090) (morpho, EOD), male, 76.0 mm SL.
Republic of the Congo, small channel
around island in Lékoli River (Congo basin), Odzala National Park (0.62° N, 14.92° E), J.P. Friel, S. Lavoué
& J.P. Sullivan coll., August 2002.
Other specimens. We examined 34 other specimens from Odzala National Park (specimen list provided
in the section "additional material examined").
LAVOUÉ ET AL.10 · Zootaxa 2600 © 2010 Magnolia Press
FIGURE 4. Petrocephalus zakoni n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88101; scale bar = 1.0 cm). C.
EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other
recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted
(head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar =
0.2 msec).
Diagnosis. Petrocephalus zakoni n. sp. is distinguished from all other Petrocephalus species in Central
Africa (Lower Guinea and Congo provinces) by the following combination of characteristics. Dorsal fin with
23 or 24 branched rays. Anal fin with 27 or 28 branched rays. Eye large (HL/ED
3.3, range = 3.1–3.3).
Mouth small (4.4
HL/MW, range = 4.4–5.0). Ten teeth or fewer (range = 6–10) in the upper jaw. Twenty-
Zootaxa 2600 © 2010 Magnolia Press · 11
PETROCEPHALUS OF ODZALA
two teeth or fewer (range = 18–22) in the lower jaw. Unique pigmentation pattern consisting of three well
defined black patches (Fig. 4A): (1) an intense dark mark on each side of the body close to the anterior base of
the dorsal fin, often extending onto the first dorsal rays, forming a characteristic saddle across the dorsum; (2)
a mark on each side of the body at the base of the pectoral fin; (3) a crescent-shaped mark on each side of the
body centered at the base of the caudal fin, extending onto the upper and lower parts of the caudal fin. EOD of
normal polarity (i.e., first major phase head-positive).
Description. Morphometric ratios and meristic data are given in Table 2 for the holotype and paratypes
separately. Petrocephalus zakoni n. sp. is a small sized species within the genus (maximum SL in the type
series = 86.0 mm, maximum SL observed in all specimens = 90 mm). Body ovoid, longer than high (2.5
SL/
H
2.8, paratype average = 2.6, holotype =2.8) and laterally compressed. Head length between 3.4 and 3.7
times in standard length (paratype average = 3.6, holotype = 3.6). Eye large compared to many Petrocephalus
species (3.1
HL/ED 3.3, paratype average = 3.2, holotype = 3.2). Snout short (6.1 HL/SNL 8.5,
paratype average = 7.2, holotype = 6.2) and round. Mouth small (4.4
HL/MW 5.0, paratype average = 4.7,
holotype = 4.5) and sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, 6–10
(paratype median = 8, holotype = 9) in a single row in the upper jaw, 18–22 (paratype median = 19, holotype
= 20) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.6
SL/PDD 1.7,
paratype average and holotype = 1.6; 1.6
SL/PAD 1.7, paratype average and holotype = 1.6). Pre-dorsal
distance roughly equal to the pre-anal distance. Dorsal fin with 23 or 24 branched rays (median = 23, holotype
= 24). Anal fin with 27 or 28 branched rays (median = 27, holotype = 28). Scales cover the body, except for
the head. Lateral line visible and complete with 36–38 pored scales along its length (paratype average = 37,
holotype = 38). Twelve to 14 scales (paratype average = 13, holotype = 14) between the anterior base of the
anal fin and the lateral line. Caudal peduncle thin (1.9
CPL/CPD 2.3, paratype average = 2.1, holotype =
2.2). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation.
Knollenorgans on the head are not clustered into "rosettes" but, instead, appear as isolated receptor pores, the
character state observed in the Mormyrinae.
Live coloration (Fig. 4A). Body uniformly white-silver, with the presence of three characteristic
pigmentation marks: (1) a very distinctive black mark just below the anterior base of the dorsal fin on each
side, often extending onto the first dorsal rays and making contact over the dorsum with the contralateral
mark; (2) a blackish mark, sometimes weak but always visible, at the base of the pectoral fins; (3) a crescent-
shaped black mark centered at the base of the caudal fin on each side, extending onto the upper and lower
parts of the caudal fin. Fins otherwise translucent.
Distribution (Fig. 1). Apparently endemic to the Congo basin. Abundant in Odzala. We collected P.
zakoni n. sp. at several localities along the main channel of the Lékoli River at night. Elsewhere in the Congo
basin, we have identified specimens of P. zakoni n. sp. from the Lower Congo (Pool Malebo) and from the
Sangha River basin (unpublished observations).
Electric organ discharge (Fig. 4C). EOD waveforms produced by P. zakoni n. sp. are of relatively short
duration among Petrocephalus (range = 0.164–0.281 msec), but they are, nevertheless, very similar in
waveform to the EODs of several other Petrocephalus species. EOD sex differences are not apparent in the
Odzala population. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué
et al. (2008). Electrocytes are assumed to be of type NPp based on characteristics of the EOD, although
electrocyte anatomy has not yet been confirmed histologically.
Remarks. Given our identification of specimens from the Lower Congo River and the Dzangha-Sangha
Reserve (Sangha River), Petrocephalus zakoni n. sp. is likely a common species in the Congo basin. This
species has been previously misidentified as Petrocephalus christyi Boulenger, 1920 because its body
proportions are similar to those of P. christyi. In addition, both species exhibit an intense sub-dorsal melanin
marking on the flank. Nevertheless, these species can be distinguished by the presence of a black spot at the
base of the pectoral fins in P. zakoni n. sp. (absent in P. christyi), the shape of the sub-dorsal marking (ovoid to
saddle-shaped versus rounded in P. christyi), the waveshape of the EOD (with two main phases and a weak
third phase in P. zakoni versus four phases in P. christyi) and presence/absence of Knollenorgan rosettes on the
head (absent in P. zakoni versus present in P. christyi).
LAVOUÉ ET AL.12 · Zootaxa 2600 © 2010 Magnolia Press
TABLE 2. Principal morphometric ratios and meristic counts for the holotype (CU 88101) and 10 paratypes (CU 88104,
CU 88093, CU 88036, CU 88077, CU 88042, CU 88037, AMNH 250920, AMNH 250921, AMNH 250922, AMNH
250923) of Petrocephalus zakoni n. sp. (Abbreviations: m= male; Std
–Dev= standard deviation; Min–Max= minimum–
maximum).
Etymology. Named in honor of Harold H. Zakon. In addition to Professor Zakon’s many contributions to
neuroethology, we recognize the significance of his recent work (Zakon et al., 2006), which inspires a new
area of research on genes that underlie electrolocation and electrical communication in gymnotiform and
mormyroid fishes.
Holotype (m) Paratypes (n=10)
Min–Max Mean Std–Dev
Standard length (mm) 86.0 67.4–84.8 77.8 5.1
Head length (mm) 23.8 19.7–24.0 21.9 1.5
Ratio of standard length (SL):
SL/body height (H) 2.8 2.5–2.7 2.6 0.1
SL/head length (HL) 3.6 3.4–3.7 3.6 0.1
SL/pre-dorsal distance (PDD) 1.6 1.6–1.7 1.6 0.0
SL/pre-anal distance (PAD) 1.6 1.6–1.7 1.6 0.0
SL/dorsal fin length (DFL) 4.2 4.0–4.3 4.1 0.1
SL/anal fin length (AFL) 3.5 3.3–3.5 3.4 0.1
SL/caudal peduncle length (CPL) 6.9 6.4–7.0 6.7 0.2
SL/mouth width (MW) 16.2 15.5–17.6 16.6 0.7
Ratio of head length (HL):
HL/snout length (SNL) 6.2 6.1–8.5 7.2 0.7
HL/mouth width (MW) 4.5 4.4–5.0 4.7 0.2
HL/eye diameter (ED) 3.2 3.1–3.3 3.2 0.1
HL/interorbital width (IOW) 3.0 2.4–3.2 2.9 0.2
HL/head width (HW) 1.9 1.8–2.0 1.9 0.0
HL/mouth position (MP) 3.4 3.2–3.9 3.5 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.2 1.9–2.3 2.1 0.1
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 24 23–24 23
Anal fin branched rays (AR) 28 27–28 27
Number of scales in the lateral line (SLL) 38 36–37 37
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
14 12–14 13
Number of teeth in the upper jaw (TUJ) 9 6–10 8
Number of teeth in the lower jaw (TLJ) 20 18–22 19
Zootaxa 2600 © 2010 Magnolia Press · 13
PETROCEPHALUS OF ODZALA
Petrocephalus valentini n. sp.
[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 3, OTU 3]
Images. Fig. 5A, photo of a live specimen from Odzala and Fig. 5B, photo of the preserved holotype (CU
88117).
Type material. Holotype, CU 88117 (morpho, EOD), male, 77.2 mm SL. Republic of the Congo,
Cuvette-Ouest, Lékoli River (Congo basin), Odzala National Park (0.62° N, 14.93° E), J.P. Friel, S. Lavoué &
J.P. Sullivan, 24 August 2002.
Paratypes. CU 87828 (morpho, EOD), sex undet., 73.6 mm SL; AMNH 251420 (ex CU 87827) (morpho,
EOD), male, 70.9 mm SL; AMNH 251423 (ex CU 88116) (morpho, EOD), sex undet., 64.5 mm SL; CU
88120 (morpho, EOD), sex undet., 66.7 mm SL; CU 88118 (morpho, EOD, DNA), sex undet., 58.1 mm SL.
Republic of the Congo, Cuvette-Ouest, Lékoli River (Congo basin), Odzala National Park (0.62° N, 14.93°E),
J.P. Friel, S. Lavoué & J.P. Sullivan coll., 24 August 2002. CU 87834 (morpho, EOD), male, 70.6 mm SL;
AMNH 251422 (ex CU 88073) (morpho, EOD), sex undet., 65.9 mm SL; AMNH 251421 (ex CU 88072)
(morpho, EOD), male, 72.9 mm SL.
Republic of the Congo, Cuvette-Ouest, Lékénie River at Mboko
débarcadère, Odzala National Park (0.62° N, 14.91° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August
2002.
Other specimens. We examined three other specimens from Odzala National Park (specimen list
provided in the section "additional material examined").
Diagnosis. Petrocephalus valentini n. sp. is distinguished from all other Petrocephalus species in Central
Africa (i.e., Lower Guinea and Congo provinces) by the following combination of characteristics. Dorsal fin
with 19–24 branched rays. Anal fin with 24–26 branched rays. Eye large (HL/ED
3.2, range = 2.9–3.2).
Mouth very small (HL/MW
5.8, range = 4.7–5.8). Twelve teeth or fewer in the upper jaw (range = 7–12), 17
teeth or fewer in the lower jaw (range = 15–17). Pigmentation pattern subtle, including two components: (1) a
pale dorsal black mark on each side of the body below the anterior base of the dorsal fin (under the second to
sixth dorsal rays); (2) an ovoid mark, sometimes scarcely visible, at the base of the caudal fin, extending
weakly onto the upper and lower lobes of the fin. EOD of normal polarity.
Description. Morphometric ratios and meristic data are given in Table 3 for the holotype and paratypes
separately. Petrocephalus valentini n. sp. is a small sized species within the genus (maximum SL = 77.2 mm,
holotype). Body ovoid, longer than high (2.8
SL/H 3.0, paratype average = 2.9, holotype = 2.8) and
laterally compressed. Head length between 3.4 and 3.7 times in standard length (paratype average = 3.6,
holotype = 3.4). Snout short (6.5
HL/SNL 8.2, paratype average = 7.4, holotype = 6.5) and round. Mouth
small (4.7
HL/MW 5.8, paratype average = 5.2, holotype = 5.1) and sub-terminal, positioned under the
anterior half of the eye. Eye large (2.9
HL/ED 3.2, paratype average = 3.0, holotype = 3.1). Teeth small
and bicuspid, 7–12 (paratype median = 9, holotype = 9) in a single row in the upper jaw, 15–17 (paratype
median = 16, holotype = 17) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body
(1.6
SL/PDD 1.7 and SL/PAD = 1.6). Pre-dorsal distance approximately equal to the pre-anal distance.
Dorsal fin with 19–24 branched rays (paratype median = 22, holotype = 22). Anal fin with 24–26 branched
rays (paratype median = 25, holotype = 25). Scales cover the body, except for the head. Lateral line visible
and complete with 35–36 pored scales along its length (paratype median = 36, holotype = 35). Nine to 12
scales (paratype median = 11, holotype = 11) between the anterior base of the anal fin and the lateral line.
Caudal peduncle relatively thin (2.2
CPL/CPD 2.5, paratype average = 2.3, holotype = 2.3). Twelve scales
around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans clearly
organized into two visible rosettes (the Augenrosette and the Nackenrosette). During our examination of
specimens, we were uncertain about the definitive presence of the third rosette, the Kehlrosette, as this
structure did not appear to us to be as distinct as it is in some other species (e.g., P. binotatus). Recently,
however, more definitive analysis using toluidine blue staining of the skin suggests that the Kehlrosette is in
fact present, but it is indeed smaller and harder to discern than in other Petrocephalus (M. Hollmann and B. A.
Carlson, unpub. obs.).
LAVOUÉ ET AL.14 · Zootaxa 2600 © 2010 Magnolia Press
TABLE 3. Principal morphometric ratios and meristic counts for the holotype (CU 88117) and eight paratypes (CU
87828, CU 87834, CU 88120, CU 88118, AMNH 250924, AMNH 250925, AMNH 250926, AMNH 250927) of
Petrocephalus valentini n. sp. (Abbreviations: m= male; Std
–Dev= standard deviation; Min–Max= minimum–
maximum).
Live coloration (Fig. 5A). Body uniformly white-silver, with two faint black patches, sometimes hardly
distinguishable: (1) a dorsal mark on each side of the body, below the anterior base of the dorsal fin under the
second to the sixth rays; (2) an ovoid/crescent-shaped mark centered at the base of the caudal fin (sometimes
the center of this second mark is less distinguishable than the two arms of the crescent), with each arm slightly
extending onto the upper and lower parts of the caudal fin. There is no melanin marking at the base of the
pectoral fins. Fins translucent.
Distribution (Fig. 1). Apparently endemic to the Congo basin. Common in Odzala National Park. At
night, we collected single specimens cruising in the main channel of the Lékoli River. At the times we
Holotype (m) Paratypes (n=8)
Min–Max Mean Std–Dev
Standard length (mm) 77.2 58.1–73.6 67.9 5.2
Head length (mm) 22.4 16.0–20.2 18.8 1.4
Ratio of standard length (SL):
SL/body height (H) 2.8 2.8–3.0 2.9 0.1
SL/head length (HL) 3.4 3.6–3.7 3.6 0.0
SL/pre-dorsal distance (PDD) 1.7 1.6–1.7 1.7 0.0
SL/pre-anal distance (PAD) 1.6 1.6–1.6 1.6 0.0
SL/dorsal fin length (DFL) 4.2 4.3–4.9 4.4 0.2
SL/anal fin length (AFL) 4.1 3.9–4.3 4.1 0.1
SL/caudal peduncle length (CPL) 5.1 5.1–5.8 5.3 0.3
SL/mouth width (MW) 17.5 17.2–20.6 18.9 1.2
Ratio of head length (HL):
HL/snout length (SNL) 6.5 6.8–8.2 7.4 0.5
HL/mouth width (MW) 5.1 4.7–5.8 5.2 0.4
HL/eye diameter (ED) 3.1 2.9–3.2 3.0 0.1
HL/interorbital width (IOW) 3.2 2.8–3.2 3.0 0.1
HL/head width (HW) 2.1 1.8–1.9 1.9 0.0
HL/mouth position (MP) 4.7 3.6–4.3 3.9 0.3
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.3 2.2–2.5 2.3 0.1
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 22 19–24 22
Anal fin branched rays (AR) 25 24–26 25
Number of scales in the lateral line (SLL) 35 35–36 36
Number of scale rows between the anterior base of the
anal fin and the lateral line (SDL)
11 9–12 11
Number of teeth in the upper jaw (TUJ) 9 7–12 9
Number of teeth in the lower jaw (TLJ) 17 15–17 16
Zootaxa 2600 © 2010 Magnolia Press · 15
PETROCEPHALUS OF ODZALA
surveyed Odzala, P. valentini seemed absent from the small tributary creeks flowing through the park’s forest
or savannah. Elsewhere in the Congo basin, P. valentini n. sp. has been collected from the Lower Congo River
in the vicinity of the Pool Malebo (museum specimen records, pers. obs.).
FIGURE 5. Petrocephalus valentini n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo.
A. Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88117; scale bar = 1.0 cm). C.
EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other
recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted
(head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar =
0.2 msec).
Electric organ discharge (Fig. 5C). The EOD waveform produced by P. valentini n. sp. is similar in its
characteristics to those produced by many other Petrocephalus species. EOD duration = 0.520 – 1.022 msec.
LAVOUÉ ET AL.16 · Zootaxa 2600 © 2010 Magnolia Press
Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008).
Electrocytes are assumed to be of type NPp based on the EOD waveform, although this has not been
confirmed histologically.
Remarks. Without careful inspection, it is possible that specimens of Petrocephalus valentini n. sp. could
be misidentified as Petrocephalus catostoma or Petrocephalus simus because of the absence or near absence
of pigmentation patterns in all three species. However, these three species differ from each other in several
morphometric measurements and meristic counts, and their geographical distributions, as currently known,
are non-overlapping.
Etymology. Named in honor of Mr. Valentin Mbossi, pinassier extraordinaire at Odzala National Park.
Fieldwork is as important as laboratory bench work and analysis when it comes to investigations of electric
fish taxonomy, behavior and evolution. Valentin assisted us during both of our expeditions to Odzala. We use
his first name for this species to reflect our appreciation of him as both colleague and friend and to avoid
confusion with a similarly named species, below.
Petrocephalus balayi Sauvage, 1883
Mormyrus catostoma – Günther (1867): 116 (non Mormyrus catostoma Günther, 1866).
Petrocephalus balayi Sauvage (1883): 159.
Mormyrus ballayi – Sauvage (1884): 195.
Petrocephalus ballayi – Pellegrin (1908): 185. ⎯ Boulenger (1909–1916): 52. ⎯ Gosse (1984): 108.
Mormyrus amblystoma Günther (1896): 281. ⎯ Boulenger (1909–1916): 52.
[Odzala field identification: Petrocephalus sp. 4, OTU 4]
Images. Fig. 6A, photo of a live specimen from Odzala, Fig. 6B, photo of a preserved specimen from Odzala
and Fig. 14, drawing of the holotype of Mormyrus amblystoma from Boulenger (1909–1916). Photos of the
preserved holotype of Petrocephalus balayi in Lavoué et al (2004) and Harder (2000).
Type material. Holotype, MNHN A 6297, sex undet., 85.5 mm SL. Gabon, Ogooué River, without more
precision, Expedition Savorgnan de Brazza, Noël Ballay coll.
Other specimens. We examined two other specimens from Odzala National Park (see specimen list
provided in the section "additional material examined"). We also examined other specimens from the Lower
Guinea province [listed in Lavoué et al. (2004)].
Diagnosis. The following diagnosis is based on all examined specimens of P. balayi, regardless their
geographic origins. Petrocephalus balayi is distinguished from all other Petrocephalus species in Central
Africa by the following combination of characteristics. Dorsal fin with 20–22 branched rays. Anal fin with 26
or 27 branched rays. Eye small (4.5
HL/ED, range = 4.5–4.9). Mouth very wide (HL/MW 3.9, range =
2.7–3.9), associated with a very characteristic head shape when viewed from below. Fourteen teeth or more in
the upper jaw (range = 14–21). Twenty-eight teeth or more in the lower jaw (range = 28–38). Melanin pattern
consisting of the following: (1) a distinct black round mark on each side of the body below dorsal fin origin;
(2) an ovoid mark on each side at the base of the caudal peduncle, not extending onto the upper and lower
parts of the caudal fin; (3) a black mark, sometimes diffuse but always present, at the base of the pectoral fins.
The EOD is of normal polarity.
Description. Table 4 presents morphometric ratios and meristic data for the holotype (from the Ogooué
River in Gabon) and for non-type specimens (from Gabon or Odzala) separately. Data given in the following
description (e.g., ranges) correspond to the two Odzala specimens we examined, except where explicit
reference is made to the holotype. Petrocephalus balayi, described by Sauvage (1883), is a large, robust
species within the genus Petrocephalus (maximum SL observed in Odzala = 95.6 mm SL, holotype = 85.5
mm SL). Body ovoid, longer than high (SL/H = 2.5–2.7, holotype = 2.8) and laterally compressed. Head
length between 3.3 and 3.4 times (holotype = 3.3) in standard length. Head width 1.9 times (holotype = 2.2) in
head length. Snout short (8.4
HL/SNL 9.3, holotype = 8.1), wide and square-shaped. Mouth wide (2.7
HL/MW
3.1, holotype = 3.4), sub-terminal, opening under the anterior half of the eye. Teeth small and
bicuspid, 30 in a single row in the lower jaw and 20–21 in the upper jaw. Eye small (4.5
HL/ED 4.8,
Zootaxa 2600 © 2010 Magnolia Press · 17
PETROCEPHALUS OF ODZALA
holotype = 4.6). Dorsal and anal fins originate in the posterior half of the body (SL/PDD = 1.6 and SL/PAD =
1.6), with pre-dorsal distance equal to pre-anal distance. Pre-dorsal distance slightly exceeds pre-anal distance
in the holotype (1.0
PDD/PAD 1.1). Dorsal fin with 22 branched rays (holotype = 21). Anal fin with 27
branched rays (holotype = 26). Scales cover the entire body, except for the head. Lateral line visible and
complete with 36 pored scales. Caudal peduncle relatively thick (1.7
CPL/CPD 1.8, holotype = 2.3).
Twelve circumpeduncular scales. Skin on head thick, becoming opaque with formalin fixation. Knollenorgans
organized into the three rosettes named by Harder (1968).
FIGURE 6. Petrocephalus balayi of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD
waveforms. One EOD was arbitrarily selected from each of two recorded individuals, and they were superimposed
together. Both EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same
time scale as an overlay centered on the largest positive peak (scale bar = 0.2 msec).
LAVOUÉ ET AL.18 · Zootaxa 2600 © 2010 Magnolia Press
TABLE 4. Principal morphometric ratios and meristic counts for the holotype (MNHN A6297), two non-type specimens
from Odzala (CU 87851, CU 88111) and seven non type specimens from Gabon of Petrocephalus balayi Sauvage, 1883.
(Abbreviations: o= sex category "other" [i.e., not an obvious mature male, but rather a female or immature male]; Std-
Dev= standard deviation; Min-Max= minimum-maximum).
*Data from Lavoué et al. (2004)
Live coloration (Fig. 6A). Body gray/silver, slightly darker dorsally. The head is also slightly darker than
the rest of the body. Iridescent pigment along side of body sometimes visible with correct orientation of light.
Pigmentation pattern with three black patches: (1) a distinct round black mark on each side of the body below
the dorsal fin origin; (2) an ovoid black mark on each side at the base of the caudal peduncle that does not
extend onto the upper and lower parts of the caudal fin; (3) a black mark, sometimes diffuse in larger
individuals but always present, at the base of the pectoral fins. The fins themselves are translucent.
Holotype
(o)*
Specimens from
Odzala (n=2)
Specimens from
Gabon (Ogooué
basin) (n=7)*
Min–Max Min–Max Mean Std–Dev
Standard length (mm) 85.5 81.3–95.6 82.2–126.0 98.3 17.9
Head length (mm) 25.9 24.2–28.6 23.3–36.0 28.4 4.8
Ratio of standard length (SL):
SL/body height (H) 2.8 2.5–2.7 2.5–3.0 2.8 0.1
SL/head length (HL) 3.3 3.3–3.4 3.3–3.6 3.5 0.1
SL/pre-dorsal distance (PDD) 1.5 1.6–1.6 1.5–1.6 1.5 0.0
SL/pre-anal distance (PAD) 1.6 1.6–1.6 1.5–1.7 1.6 0.0
SL/dorsal fin length (DFL) 4.5 4.2–4.4 4.3–5.1 4.8 0.2
SL/anal fin length (AFL) 3.8 3.5–3.5 3.4–4.0 3.8 0.3
SL/caudal peduncle length (CPL) 5.7 6.9–7.0 5.1–6.6 6.0 0.4
SL/mouth width (MW) 11.2 9.0–10.4 9.3–13.7 11.1 1.3
Ratio of head length (HL):
HL/snout length (SNL) 8.1 8.4–9.3 5.4–7.6 6.2 0.9
HL/mouth width (MW) 3.4 2.7–3.1 2.7–3.9 3.3 0.4
HL/eye diameter (ED) 4.6 4.5–4.8 4.5–4.9 4.7 0.1
HL/interorbital width (IOW) 3.2 3.0–3.0 2.6–3.1 2.8 0.2
HL/head width (HW) 2.2 1.9–1.9 1.6–2.0 1.9 0.1
HL/mouth position (MP) 5.9 4.7–4.9 5.0–5.7 5.5 0.3
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.3 1.7–1.8 1.9–2.2 2.0 0.1
Min–Max Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 21 22–22 20–22 22
Anal fin branched rays (AR) 26 27–27 26–27 26
Number of scales in the lateral line (SLL) 38 36–36 35–37 36
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
11 10–10 10–12 11
Number of teeth in the upper jaw (TUJ) 16 20–21
30–30
14–18 -
Number of teeth in the lower jaw (TLJ) 38 28–37 -
Zootaxa 2600 © 2010 Magnolia Press · 19
PETROCEPHALUS OF ODZALA
Distribution (Fig. 1). Petrocephalus balayi occurs in the southern part of the Lower Guinea province and
in the Congo River basin, including Odzala and the Lower Congo River (David & Poll, 1937; Lavoué et al.,
2004; Poll, 1939; Sauvage, 1883). In Odzala, Petrocephalus balayi seems to prefer the small tributary creeks
flowing through forest. In Gabon (Lower Guinea province), P. balayi occurs in the lower courses of the
Ogooué River and numerous associated lakes (and their tributary streams), as well as in small coastal creeks
from south of the Ogooué to the Congo River basin. Records from the upper part of the Lower Guinea
province and elsewhere appear to be misidentifications (pers. obs.).
Electric organ discharge (Fig. 6C). EOD recordings are only available for a small number of
individuals: one specimen from the coastal river Doumvou at Doumvou, Gabon [03.33S–10.73E] (S. Lavoué
& V. Mamonekene coll., 24 July 2001) (Lavoué et al., 2004); and two specimens from Odzala National Park,
Republic of the Congo (Lavoué et al., 2008). Among these few recordings, the overall waveform of EODs
produced by P. balayi seems to be typical for the genus, similar to those produced by several other
Petrocephalus species. EOD duration = 0.324 – 0.340 msec. Statistics for waveform landmarks and other
EOD measurements are provided by Lavoué et al. (2008), who confirmed histologically that electrocytes in P.
balayi are of type NPp.
Remarks. Almost all measurements and meristic counts of Odzala specimens fall within the range of
values defined by the holotype and other specimens from Gabon. The EOD waveforms of the Odzala
specimens and those from Gabon are similar (Lavoué et al., 2004).
Petrocephalus microphthalmus Pellegrin, 1908
Petrocephalus microphthalmus Pellegrin (1908): 185.
[Odzala field identification: Petrocephalus sp. 5, OTU 5]
Images. Fig. 7A, photo of a live specimen from Odzala, Fig. 7B, photo of a preserved specimen from Odzala
and Fig. 14, drawing from Poll (1967) of a specimen collected in Angola. Photo of the holotype (MNHN
1908–211) in Lavoué et al. (2004).
Type material. Holotype, MNHN 1908–211, male, 73.7 mm SL. Gabon, Ogooué basin at Ngomo (Lower
Ogooué) [estimated 0.82S, 9.95E], E. Haug coll.
Other specimens. We examined 14 other specimens from Odzala National Park (specimen list provided
in the section "additional material examined"). A list of additional specimens examined from Lower Guinea is
given in Lavoué et al. (2004).
Diagnosis. We prepared the following diagnosis using all the specimens of P. microphthalmus that we
examined, regardless their geographic origins. Petrocephalus microphthalmus is distinguished from all other
Petrocephalus species in Central Africa by the following combination of characteristics. Short dorsal fin with
only 18 or fewer branched rays (range 15–18). Long anal fin with 23–27 branched rays. Eye small (4.0
HL/
ED, range = 4.1–4.8). Mouth moderately wide (3.5
HL/MW 4.9). Only 9–11 teeth in the upper jaw, 14–20
teeth in the lower jaw. Absence of black pigment patches, except for a characteristic black blotch on the
anterior dorsal fin rays near the origin of this fin. Body silvery/purplish, iridescent. Electroreceptors on the
head are not clustered into "rosettes" but, instead, appear as isolated receptor pores. EOD of normal polarity
with two main phases and, in Odzala, a third minute phase of very low amplitude.
Description. Morphometric ratios and meristic data for the holotype (from Gabon) and the non-type
specimens (from Odzala and Lower Guinea) are presented in Table 5. However, the following description is
based only on the Odzala specimens we examined, except where we make separate reference to the holotype.
With a maximum observed standard length of 59.1 mm in Odzala National Park, P. microphthalmus is the
smallest species in the diverse Odzala assemblage of Petrocephalus. Body ovoid, longer than high (2.6
SL/
H
2.8, holotype = 2.7) and laterally compressed. Head length between 3.8 and 4.0 times in standard length
(average = 3.9, holotype = 4.0). Snout short (5.2
HL/SNL 6.4, average = 5.8, holotype = 4.6) and round.
Mouth small (3.6
HL/MW 4.2, average = 3.9, holotype = 3.8), opening under the eye. Teeth small and
bicuspid, 9–11 (holotype = 10) in a single row in the upper jaw, 14–16 (holotype = 20) in a single row in the
LAVOUÉ ET AL.20 · Zootaxa 2600 © 2010 Magnolia Press
FIGURE 7. Petrocephalus microphthalmus of the Lékoli River system of Odzala National Park, Republic of the Congo.
A. Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD
waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings
(N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive
up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).
lower jaw. Dorsal and anal fins originate in the posterior half of the body (SL/PDD = 1.5 and SL/PAD = 1.7).
Pre-dorsal distance slightly greater than pre-anal distance (PDD/PAD
1.1). Dorsal fin with 16–18 branched
rays (holotype = 16). Anal fin with 26–27 branched rays (holotype = 25). Scales cover the entire body, except
for the head. Lateral line visible and complete with 34 to 35 pored scales along its length (holotype = 36).
Zootaxa 2600 © 2010 Magnolia Press · 21
PETROCEPHALUS OF ODZALA
Eight to 10 scales between the anterior base of the anal fin and the lateral line. Twelve scales around the
caudal peduncle. Skin on head thick, becoming opaque with formalin fixation, containing numerous
Knollenorgan electroreceptors that do not form "rosettes" in their typical positions. Instead, Knollenorgans
appear as isolated receptor pores in the skin covering the head, the character state observed in the
Mormyrinae.
TABLE 5. Principal morphometric ratios and meristic counts for the holotype (MNHN 1908-211), three specimens from
Odzala (CU 87938, CU 87940, CU 88003) and 36 specimens from Gabon of Petrocephalus microphthalmus Pellegrin,
1908. (Abbreviations: m= male; Std–Dev= standard deviation; Min–Max= minimum–maximum).
*Data from Lavoué et al. (2004)
Holotype
(m)*
Specimens
from Odzala
(n=3)
Specimens from
Gabon (Ogooué
River) (n=36)*
Min–Max Mean Std–Dev Min–Max Mean Std–Dev
Standard length (mm) 73.7 51.8–59.1 54.7 3.8 52.1–69.9 59.4 4.6
Head length (mm) 18.3 13.4–14.9 14.0 0.8 14.0–16.7 15.1 0.9
Ratio of standard length (SL):
SL/body height (H) 2.7 2.6–2.8 2.7 0.1 2.7–3.2 3.0 0.2
SL/head length (HL) 4.0 3.8–4.0 3.9 0.1 3.6–4.3 3.9 0.2
SL/pre-dorsal distance (PDD) 1.5 1.5–1.5 1.5 0.0 1.5–1.7 1.6 0.1
SL/pre-anal distance (PAD) 1.7 1.7–1.7 1.7 0.0 1.6–1.9 1.8 0.1
SL/anal fin length (AFL) 5.4 5.0–5.3 5.2 0.2 4.9–6.5 5.5 0.4
SL/dorsal fin length (DFL) 3.3 3.3–3.4 3.3 0.0 3.2–3.9 3.5 0.2
SL/caudal peduncle length (CPL) 5.5 5.5–5.9 5.8 0.2 4.4–5.7 5.1 0.3
SL/mouth width (MW) 15.4 14.2–16.3 15.4 1.1 13.7–19.2 16.3 0.8
Ratio of head length (HL):
HL/snout length (SNL) 4.6 5.2–6.4 5.8 0.6 4.1–6.2 4.7 0.4
HL/mouth width (MW) 3.8 3.6–4.2 3.9 0.3 3.5–4.9 4.2 0.4
HL/eye diameter (ED) 4.8 4.0–4.5 4.2 0.2 4.1–4.8 4.5 0.2
HL/interorbital width (IOW) 2.6 2.6–3.1 2.8 0.3 2.0–2.8 2.5 0.2
HL/head width (HW) 1.7 1.6–2.0 1.8 0.2 1.7–2.0 1.8 0.1
HL/mouth position (MP) 3.4 3.6–4.2 3.9 0.3 2.8–3.7 3.2 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.9 2.7–2.7 2.7 0.0 2.6–3.7 3.0 0.4
Min–Max Median Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 16 16–18 17 15–18 16
Anal fin branched rays (AR) 25 26–27 27 23–27 25
Number of scales in the lateral line (SLL) 36 34–35 35 33–36 35
Number of scale rows between the
anterior base of the anal fin and the
lateral line (SDL)
10 8–10 9 8–10 9
Number of teeth in the upper jaw (TUJ) 10 9–11 10 9–11 10
Number of teeth in the lower jaw (TLJ) 20 14–16 15 14–20 16
LAVOUÉ ET AL.22 · Zootaxa 2600 © 2010 Magnolia Press
Live coloration (Fig. 7A). Body generally blue-gray, with the dorsum darker than the abdomen.
Numerous chromatophores occur below the skin surface. This species can appear metallic blue to violet
depending on the angle and intensity of illumination. The color is especially intense on the operculum. The
fins are translucent except for the first dorsal fin rays, which are black near their insertion (Lavoué et al.,
2004).
Distribution (Fig. 1). Present in Congo and Lower Guinea provinces. Holotype from Gabon. Abundant in
Odzala, where we collected P. microphthalmus in small tributary creeks flowing through forest. Elsewhere in
the Congo basin it is present in the Lower Congo River in the vicinity of Brazzaville. In the Lower Guinea
province this species is widespread throughout the entire Ogooué and Ntem basins in Gabon, including
streams and lakes associated with main river channels (e.g., Lac Zilé). It can also be found along the coastal
region from the Sanaga River (Cameroon) in the north to the more southern Niari-Kouilou River (
Republic of
the Congo
).
Electric organ discharge (Fig. 7C). Petrocephalus microphthalmus produces EODs of short duration,
which are typical of the entire genus. No sex differences have yet been reported in any population. Similar
EOD durations have been observed in the Odzala population of P. microphthalmus [range = 0.252 – 0.511
msec; Lavoué et al. (2008)] and among conspecifics from Gabon [range = 0.380 – 0.561 msec; Lavoué et al.
(2004)]. A relatively long, slow rise characterizes the initial part of the first head-positive phase in EODs
recorded from the Odzala population, often resulting in a shoulder early during the waveform’s head-positive
rise to P1, the first main peak (Lavoué et al., 2008). The early head-positive rise and shoulder are very low in
amplitude, however, such that they may only be apparent at high amplifier gain. These subtle waveform
features appear to be uncommon in EODs of other Petrocephalus species. A similar slow rise (and shoulder)
preceding P1 has been recorded among a small number of P. microphthalmus individuals from Gabon, but it
seems to be much less common than in Odzala. Additional statistics for waveform landmarks and other EOD
measurements for the Odzala population are provided by Lavoué et al. (2008). Based on histological
examination, electrocytes are known to be type NPp (Lavoué et al., 2008; Sullivan et al., 2000).
Remarks. Petrocephalus microphthalmus closely resembles Petrocephalus schoutedeni Poll, 1954 and
Petrocephalus catostoma haullevillii Boulenger, 1912. Petrocephalus microphthalmus is distinguished from
P. schoutedeni mainly by the shape of the caudal peduncle: in the Odzala specimens its length is only 2.7
times (holotype = 2.9 times) its depth, versus 3.4–3.7 times in P. schoutedeni. We did not find any
unambiguous morphological differences with which to distinguish P. microphthalmus and P. catostoma
haullevillii.
Petrocephalus odzalaensis n. sp.
[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 6, OTU 6]
Images. Fig. 8A, photo of a live specimen from Odzala and Fig. 8B, photo of the preserved holotype (CU
88048).
Type material. Holotype, CU 88048 (morpho, EOD), sex undet., 92.9 mm SL. Republic of the Congo,
Lékénie River at Mboko débarcadère (Congo basin), Odzala National Park, (0.62° N, 14.90° E), J.P. Friel, S.
Lavoué & J.P. Sullivan coll., August 2002.
Paratypes. CU 87850 (morpho, EOD), male, 90.1 mm SL; CU 87857 (morpho, EOD), male, 92.6 mm SL;
CU 88050 (morpho, EOD), male, 90.4 mm SL; AMNH 251414 (ex CU 87843) (morpho, EOD), male, 87.0
mm SL; AMNH 251417 (ex CU 88056) (morpho, EOD), male, 87.6 mm SL; AMNH 251416 (ex CU 88054)
(morpho, EOD), male, 97.6 mm SL; CU 88059 (morpho, EOD), male, 99.3 mm SL; AMNH 251415 (ex CU
87844) (morpho, EOD), male, 87.3 mm SL.
Republic of the Congo, Lékénie River at Mboko débarcadère
(Congo basin), Odzala National Park, (0.62° N, 14.90° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August
2002. CU 88049 (morpho, EOD; caudal peduncle dissected by Lavoué et al. (2008) to sample electric organ
for histological examination), male, 93.2 mm SL.
Republic of the Congo, Lékénie River at Mboko
Zootaxa 2600 © 2010 Magnolia Press · 23
PETROCEPHALUS OF ODZALA
débarcadère (Congo basin), Odzala National Park, (0.62° N, 14.90° E), J.P. Friel, S. Lavoué & J.P. Sullivan
coll., 12 August 2002.
FIGURE 8. Petrocephalus odzalaensis n. sp. of the Lékoli River system of Odzala National Park, Republic of the
Congo
. A. Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88048; scale bar = 1.0
cm). C. EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the
other recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted
(head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar =
0.2 msec).
LAVOUÉ ET AL.24 · Zootaxa 2600 © 2010 Magnolia Press
TABLE 6. Principal morphometric ratios and meristic counts for the holotype (CU 88048) and nine paratypes (CU
87857, CU 88049, CU 87850, CU 88050, CU 88059, AMNH 250928, AMNH 250929, AMNH 250930, AMNH 250931)
of Petrocephalus odzalaensis n. sp. (Abbreviations: o= sex category "other" [i.e., not an obvious mature male, but rather
a female or immature male]; Std–Dev= standard deviation; Min–Max= minimum–maximum).
Other specimens. We examined 19 other specimens from Odzala National Park (specimen list provided
in the section "additional material examined").
Diagnosis. Petrocephalus odzalaensis n. sp. is distinguished from all other Petrocephalus species in
Central Africa by the following combination of characteristics. Dorsal fin shorter than anal fin. Dorsal fin
with a maximum of 22 branched rays (range = 20–22). Anal fin with a minimum of 27 branched rays (range =
27–29). Mouth sub-terminal; ratio between head length and mouth position is between 4.2 and 5.0. Eye small
(3.7
HL/ED 4.2). Body pinkish-gray, darker dorsally, with the presence of three distinct pigmentation
patches: (1) a distinct ovoid black mark situated below the anterior base of the dorsal fin on each side of the
Holotype (o) Paratypes (n=9)
Min–Max Mean Std–Dev
Standard length (mm) 92.9 87.0–99.3 91.7 4.5
Head length (mm) 23.3 22.7–26.6 23.7 1.6
Ratio of standard length (SL):
SL/body height (H) 2.6 2.7–2.9 2.8 0.0
SL/head length (HL) 4.0 3.7–4.0 3.9 0.1
SL/pre-dorsal distance (PDD) 1.6 1.5–1.6 1.6 0.0
SL/pre-anal distance (PAD) 1.7 1.6–1.7 1.6 0.0
SL/dorsal fin length (DFL) 4.5 4.4–4.7 4.6 0.2
SL/anal fin length (AFL) 3.3 3.3–3.6 3.4 0.1
SL/caudal peduncle length (CPL) 6.9 6.1–7.1 6.8 0.3
SL/mouth width (MW) 17.4 16.0–18.3 16.8 0.8
Ratio of head length (HL):
HL/snout length (SNL) 6.6 6.2–8.3 7.3 0.7
HL/mouth width (MW) 4.3 4.0–4.8 4.3 0.2
HL/eye diameter (ED) 3.7 3.8–4.2 4.0 0.1
HL/interorbital width (IOW) 2.7 2.5–3.0 2.8 0.2
HL/head width (HW) 1.7 1.7–1.8 1.7 0.1
HL/mouth position (MP) 4.7 4.2–5.0 4.5 0.3
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.1 1.9–2.3 2.1 0.1
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 22 20–22 21
Anal fin branched rays (AR) 29 27–29 28
Number of scales in the lateral line (SLL) 38 36–38 37
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
11 10–14 12
Number of teeth in the upper jaw (TUJ) 11 8–12 11
Number of teeth in the lower jaw (TLJ) 18 18–23 20
Zootaxa 2600 © 2010 Magnolia Press · 25
PETROCEPHALUS OF ODZALA
body; (2) a small black mark at the base of each pectoral fin; (3) an ovoid black mark on each side that is
centered at the base of the caudal fin, not extending onto the upper and lower lobes of this fin. EOD of normal
polarity, appearing triphasic at low gain, with two main phases and a small third phase. A final, fourth phase
may be present, but it is always extremely small (< 1.5% of total peak-to-peak amplitude).
Description. Morphometric ratios and meristic data for the holotype and paratypes are presented in Table
6. Petrocephalus odzalaensis n. sp. is a medium sized species within the genus (maximum SL observed =
99.3 mm; holotype = 92.9 mm). Body ovoid, longer than high (2.6
SL/H 2.9, paratype average = 2.8,
holotype = 2.6) and laterally compressed. Head length between 3.7 and 4.0 times in standard length (paratype
average = 3.9, holotype = 4.0). Snout short (6.2
HL/SNL 8.3, paratype average = 7.3, holotype = 6.6) and
round. Mouth small (4.0
HL/MW 4.8, paratype average = 4.3, holotype = 4.3), sub-terminal, opening just
under the anterior half of the eye. Teeth small and bicuspid, 8–12 in a single row in the upper jaw (paratype
median = 11, holotype = 11), 18–23 in a single row in the lower jaw (paratype median = 20, holotype = 18).
Dorsal and anal fins originate in the posterior half of the body (1.5
SL/PDD 1.6 and 1.6 SL/PAD 1.7,
respectively). Pre-dorsal distance slightly greater than the pre–anal distance (1.0
PDD/PAD 1.1). Dorsal
fin with 20–22 branched rays (paratype median = 21, holotype = 22). Anal fin with 27–29 branched rays
(paratype median = 28, holotype = 29). Scales cover the body, except for the head. Lateral line visible and
complete with 36–38 (holotype = 38) pored scales along its length. Ten to 14 scales (paratype average = 12,
holotype = 11) between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.9
CPL/
CPD
2.3, paratype average = 2.1, holotype = 2.1). Twelve scales around the caudal peduncle. Skin on head
thick, turning opaque with formalin fixation. Knollenorgans clustered into the three distinct "rosettes" of
Harder (1968).
Live coloration (Fig. 8A). Body background color pinkish-gray, darker dorsally. Pigmentation pattern
consisting of three characteristic black patches: (1) a distinct ovoid black mark below the anterior base of the
dorsal fin; (2) a small black mark at the base of the pectoral fin; and (3) an ovoid black mark centered at the
base of the caudal fin, which does not extend onto the upper and lower lobes. Fins translucent.
Distribution (Fig. 1). Endemic to the Congo basin. Abundant in Odzala. We collected P. odzalaensis n.
sp. at several localities along the main course of the Lékoli River and in some small tributary creeks flowing
through forest.
Electric organ discharge (Fig. 8C). The EOD waveform is typical for the genus, similar to EODs
produced by many other Petrocephalus species. Total EOD duration ranges from 0.231 to 0.339 msec, based
on 1.5% voltage deviations from baseline relative to peak-peak amplitude. No EOD sex differences are
apparent in the specimens recorded thus far. Lavoué et al. (2008) provide additional statistics for waveform
landmarks and other EOD measurements. Histological examination confirms that electrocytes are type NPp
(Lavoué et al., 2008).
Remarks. Based on museum records from the Congo basin (pers. obs.), Petrocephalus odzalaensis has
been misidentified as Petrocephalus simus in several instances. The latter species is endemic to the Lower
Guinea province (Lavoué et al., 2004).
Etymology. Named for Odzala National Park.
Petrocephalus christyi Boulenger, 1920
Petrocephalus christyi Boulenger (1920): 11.
[Odzala field identification: Petrocephalus sp.7, OTU 7]
Images. Fig. 9A, photo of a live specimen from Odzala, Fig. 9B, photo of a preserved specimen from Odzala
and Fig. 14, drawing of a syntype from Boulenger (1920), p.11. Additional photo of a syntype in Harder
(2000).
Type material. Syntypes, MRAC 7145–7151 [five of seven specimens examined]. Democratic Republic
of the Congo
, Congo basin, tributary Lindi at Bosabangui [in the vicinity of Kisangani, estimated 0.53N,
25.19E], C. Christy coll. [Note that no holotype was designated in the original description of P. christyi.]
LAVOUÉ ET AL.26 · Zootaxa 2600 © 2010 Magnolia Press
FIGURE 9. Petrocephalus christyi of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD
waveforms. One EOD was arbitrarily selected from each of two recorded individuals, and they were superimposed
together. Both EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same
time scale as an overlay centered on the largest positive peak (scale bar = 0.2 msec).
Other specimens. We examined two specimens from Odzala National Park and 16 additional specimens
from the Sangha River and the Lower Congo River in the vicinity of the Pool Malebo (see specimen list
provided in the section "additional material examined").
Zootaxa 2600 © 2010 Magnolia Press · 27
PETROCEPHALUS OF ODZALA
TABLE 7. Principal morphometric ratios and meristic counts for five syntypes (MRAC 7145-7151), two specimens
from Odzala (CU 88095, CU 88057) and 16 specimens from the Lower Congo and Sangha River (AMNH collection and
four uncatalogued specimens, see text) of Petrocephalus christyi Boulenger 1920 (Abbreviations: Std–Dev= standard
deviation; Min–Max= minimum–maximum).
Diagnosis. The following diagnosis is based on all examined specimens of P. christyi, regardless their
geographic origins. Petrocephalus christyi is distinguished from all other Petrocephalus species in Central
Africa by the following combination of characteristics. Dorsal fin with 22–24 branched rays. Anal fin with
25–29 branched rays. Eye large (HL/ED
4.2, range = 3.1–4.2). Mouth small (HL/MW 2.9, range = 2.9–
Syntypes
(n=5)
Specimens
from Odzala
(n=2)
Specimens from
Lower Congo and
the Sangha River
(n=16)
Min–Max Mean Std–Dev Min–Max Min–Max Mean Std–Dev
Standard length (mm) 65.1–
100.0
89.5 12.7 50.5–84.7 67.0–109.6 82.5 12.7
Head length (mm) 18.7–26.9 24.5 3.0 16.0-24.2 19.7–30.3 23.6 3.5
Ratio of standard length (SL):
SL/body height (H) 3.0–3.2 3.1 0.1 2.7–2.9 2.6–2.8 2.7 0.1
SL/head length (HL) 3.5–3.7 3.6 0.1 3.2–3.5 3.2–3.8 3.5 0.1
SL/pre-dorsal distance (PDD) 1.6–1.7 1.6 0.0 1.6–1.6 1.5–1.6 1.6 0.0
SL/pre-anal distance (PAD) 1.6–1.7 1.6 0.0 1.6–1.6 1.6–1.8 1.7 0.0
SL/dorsal fin length (DFL) 4.1–4.4 4.2 0.1 4.3–4.4 4.1–4.4 4.2 0.1
SL/anal fin length (AFL) 3.6–3.8 3.7 0.1 3.7–4.0 3.2–3.7 3.5 0.1
SL/caudal peduncle length (CPL) 5.5–6.1 5.7 0.3 5.7–5.8 5.3–6.5 5.9 0.3
SL/mouth width (MW) 17.7–20.1 18.8 1.0 13.6–14.3 10.7–15.3 12.9 1.4
Ratio of head length (HL):
HL/snout length (SNL) 5.3–5.7 5.5 0.1 5.3–6.3 4.9–6.7 5.7 0.5
HL/mouth width (MW) 4.7–5.5 5.2 0.4 4.1–4.3 2.9–4.3 3.7 0.5
HL/eye diameter (ED) 3.1–3.8 3.5 0.2 3.2–3.4 3.3–4.2 3.7 0.3
HL/interorbital width (IOW) 2.8–3.6 3.2 0.3 2.9–3.3 2.4–3.1 2.8 0.2
HL/head width (HW) 1.9–2.2 2.1 0.1 1.7–1.9 1.7–2.1 1.8 0.2
HL/mouth position (MP) 3.2–3.5 3.4 0.1 2.9–3.0 2.6–3.4 2.9 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.5–3.0 2.7 0.2 2.5–2.6 2.4–3.0 2.6 0.2
Min–Max Median Min–Max Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 23–24 24 22–23 22–24 23
Anal fin branched rays (AR) 26–27 27 25–26 25–29 27
Number of scales in the lateral line (SLL) 35–39 37 35–37 35–37 36
Number of scale rows between the
anterior base of the anal fin and the lateral
line (SDL)
13–14 14 14–15 13–20 18
Number of teeth in the upper jaw (TUJ) 9–10 9–13 11
Number of teeth in the lower jaw (TLJ) 19–21 17–22 19
LAVOUÉ ET AL.28 · Zootaxa 2600 © 2010 Magnolia Press
5.5, but see remarks). Nine to 13 teeth in the upper jaw, 17–22 teeth in the lower jaw. Melanin patterning
consisting of two characteristic black patches: (1) a distinct round mark below the anterior base (first to the
fifth rays) of the dorsal fin; and (2) a somewhat diffuse crescent-like mark, centered at the base of the caudal
fin and extending onto the fleshy dorsal and ventral lobes of this fin. In the small number of individuals
recorded so far, the EOD is of normal polarity, with four phases and a relatively slow initial rise.
Description. Morphometric and meristic data for the syntypes, non-type specimens from Odzala and
specimens from Lower Congo are separately presented in Table 7. However, the following description
corresponds only to the new material collected from Odzala National Park, except where separate reference is
made to the Lindi River syntypes. Petrocephalus christyi is a medium-sized species within the genus
(maximum SL observed in Odzala = 84.7 mm; maximum SL observed in the syntypes = 100.0 mm). Body
ovoid, longer than high (2.7
SL/H 2.9, syntypes = 3.0–3.2) and laterally compressed. Head length between
3.2 and 3.5 times in standard length (syntypes = 3.5–3.7). Snout of intermediate size (5.3
HL/SNL 6.3,
syntypes = 5.3–5.7) and round. Eye large (3.2
HL/ED 3.4, syntypes = 3.1–3.8). Mouth small (4.1 HL/
MW
4.3, syntypes = 4.7–5.5), sub-terminal, opening just under the anterior half of the eye. Teeth small and
bicuspid, 9 or 10 in a single row in the upper jaw, 19–21 in the lower jaw. Dorsal and anal fins originate in the
posterior half of the body, with pre-dorsal distance equal to pre-anal distance (SL/PDD = 1.6 and SL/PAD =
1.6). Dorsal fin with 22 or 23 branched rays (syntypes = 23 or 24). Anal fin with 25 or 26 branched rays
(syntypes = 26 or 27). Scales cover the body, except for the head. Lateral line visible and complete with 35–37
(syntypes = 35–39) pored scales along its length. Fourteen to 15 scales (syntypes = 13 or 14) between the
anterior base of the anal fin and the lateral line. Caudal peduncle relatively thin (2.5
CPL/CPD 2.6,
syntypes = 2.5–3.0). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with
formalin fixation, with numerous electroreceptors organized into three distinct rosettes. However, the
Augenrosette (above the eye) is not as developed as it is in the other species of Petrocephalus exhibiting this
rosette.
Live coloration (Fig. 9A). Body uniformly white-silver, with the presence of two characteristic melanin
marks: (1) a distinct round mark below the anterior base (first to fifth rays) of the dorsal fin; (2) a rather
diffuse crescent-like mark, centered at the base of the caudal fin and extending onto the upper and lower
fleshy lobes of this fin. The fins themselves are translucent.
Distribution (Fig. 1). Endemic to the Congo River basin. The type specimens were collected at the
locality Bosabangui along the Lindi River, which is close to the city of Kisangani. Petrocephalus christyi
seems to be rare in Odzala, where we only collected it in the main channel of the Lékoli River at night. In
contrast, Petrocephalus christyi seems to be abundant in the vicinity of the Pool Malebo (Lower Congo).
Electric organ discharge (Fig. 9C). Bearing in mind that recordings are only available for two specimens
collected within Odzala, the EOD of this species does appear to be distinctive. The EOD exhibits normal
polarity and is four-phasic with a large, negative-going P2 and smaller peaks, P1, P3 and P4 [see Lavoué et al.
(2008) for definitions of these waveform landmarks]. Similar to the EODs of the Odzala population of P.
microphthalmus, a relatively long, slow rise occurs during the initial part of the first head-positive phase in the
EODs of both individuals of P. christyi. This rise toward P1 has a shoulder-like inflection point, which at
magnified gain is seen to possess a small, negative-going local peak. Both the slow rise and inflection point
are subtle features of the EOD; they are only visible in amplified traces. Unlike the EODs of P.
microphthalmus, however, those of the two P. christyi individuals possess a prominent head-negative fourth
peak (P4), the amplitude of which is 4.5 – 8.6 % of the waveform’s total peak-to-peak swing. A prominent P4
is also present in the EOD emitted by the only individual of Petrocephalus mbossou n. sp. ever recorded (see
below), but otherwise a P4 seems to be rare in Petrocephalus. Based on 1.5% voltage deviations from baseline
relative to peak-peak amplitude and at ambient recording temperatures, duration of the EOD is between 0.284
and 0.390 msec in P. christyi, falling in the range of many other Petrocephalus species. Statistics for
waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008). Electrocyte
anatomy is presumed to be of type NPp based on the EOD waveform, but this has not yet been confirmed
histologically.
Zootaxa 2600 © 2010 Magnolia Press · 29
PETROCEPHALUS OF ODZALA
Remarks. Specimens of P. christyi from Odzala appear to differ notably from the syntypes of P. christyi
(from the Lindi River, Fig. 1) in only a single aspect of morphological variation: mouth size. The syntypes
have smaller mouths than the Odzala specimens (SL/MW = 17.7–20.1 in the syntypes versus 13.6–14.3 in the
Odzala specimens; see also the HL/MW ratios in Table 7). Interestingly, specimens from the Lower Congo in
the vicinity of the Pool Malebo (Table 7) all have mouths similar in relative size to those of the Odzala
specimens. The magnitude of divergence in mouth size relative to the syntypes, and the fact that divergence in
this character is consistent for both Odzala and Lower Congo specimens, suggests that populations from these
sites may represent a distinct species from the P. christyi type material. A sound evaluation of this possible
difference requires additional material from other Congo River sites. Until such material becomes available,
we conservatively assign the Odzala and Lower Congo specimens described herein to P. christyi.
Petrocephalus sauvagii (Boulenger, 1887)
Mormyrus (Petrocephalus) sauvagii Boulenger (1887): 149.
Mormyrus sauvagii Steindachner (1895): 69.
Petrocephalus sauvagii Boulenger (1898): 19 ⎯ Taverne (1972): 162 ⎯ Gosse (1984): 113.
[Odzala field identification: Petrocephalus sp. 8, OTU 8]
Images. Fig. 10A, photo of a live specimen from Odzala, Fig. 10B, photo of a preserved specimen from
Odzala and Fig. 14, drawing of the holotype (BMNH 1887.1.13.3) from Boulenger (1909–1916). Photo of the
holotype in Harder (2000).
Type material. Holotype, BMNH 1887.1.13.3 "in the creeks of the Lower Congo and the tributary
streams, without more precision, unknown coll."
Other specimens. We examined six specimens from Odzala and four additional specimens from the
Lower Niger River (specimen list provided in the section "additional material examined").
Diagnosis. We prepared the following diagnosis using all the specimens of P. sauvagii that we examined,
regardless their geographic origins. Petrocephalus sauvagii is distinguished from all other Petrocephalus
species in Central Africa by the following combination of characteristics. Very wide mouth (HL/MW
3.7,
range = 2.7–3.7) associated with a characteristic head shape when viewed from below. Twenty-four to 30
teeth in the upper jaw and 30–34 in the lower jaw. Anal fin with at least 32 branched rays (range = 32–38).
Dorsal fin with at least 25 branched rays (range = 25–30). Mouth sub-terminal; ratio between the head length
and the mouth position as large as 7.4 (range = 5.5–7.4). Pigmentation pattern with two melanin markings,
sometimes of weak intensity or even scarcely visible: (1) an irregularly round black mark below the anterior
base (first to fourth rays) of the dorsal fin; and (2) an ovoid blackish mark, often irregularly shaped, at the base
of the caudal fin, extending onto the upper and lower fleshy lobes of the fin. EOD of normal polarity, with two
main phases followed by a third, smaller phase.
Description. Table 8 provides morphometric ratios and meristic data for the holotype, six non-type
specimens from Odzala and four non-type specimens from the Lower Niger River. However, the following
description corresponds only to the six Odzala specimens we examined, except where separate reference is
made to the holotype. Petrocephalus sauvagii is the largest Petrocephalus species occurring in the Odzala
assemblage (maximum SL observed in Odzala = 189.0 mm, holotype = 146.7 mm). Body ovoid, longer than
high (2.7
SL/H 3.4, average = 3.0, holotype = 2.9) and laterally compressed. Head length between 3.5 and
3.7 times in standard length (average = 3.6, holotype = 3.7). Eye small (4.1
HL/ED 4.5, average = 4.3,
holotype = 4.6). Snout very short (6.3
HL/SNL 9.9, average = 8.0, holotype = 6.7) and round. Mouth
distinctively large (3.1
HL/MW 3.7, average = 3.3, holotype = 3.1), sub-terminal (5.5 HL/MP 7.4,
average = 6.6, holotype = 4.9), opening just under the anterior half of the eye. Dentition consisting of many
small bicuspid teeth, 24–30 (median = 26, holotype = 26) in a single row in the upper jaw, 30–34 (median =
32, holotype = 30) in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the
body (1.5
SL/PDD 1.6 and 1.5 SL/PAD 1.7). Pre-dorsal distance equal to, or slightly greater than, pre-
anal distance (1.0
PDD/PAD 1.1). Anal fin with 33–38 branched rays (median = 35, holotype = 34).
LAVOUÉ ET AL.30 · Zootaxa 2600 © 2010 Magnolia Press
Dorsal fin with 26–30 branched rays (median = 28, holotype = 27). Scales cover the body, except for the head.
Lateral line visible and complete with 38–41 (median = 39, holotype = 36) pored scales along its length.
Twelve to 16 scales (median 14, holotype = 14) between the anterior base of the anal fin and the lateral line.
Caudal peduncle relatively thin (2.3
CPL/CPD 3.1, average = 2.6, holotype = 2.7). Twelve scales around
the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation, with Knollenorgan
electroreceptors organized into three relatively small rosettes.
FIGURE 10. Petrocephalus sauvagii of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD
waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings
(N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive
up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).
Zootaxa 2600 © 2010 Magnolia Press · 31
PETROCEPHALUS OF ODZALA
TABLE 8. Principal morphometric ratios and meristic counts for the holotype (BMNH 1887.1.13.3), six specimens from
Odzala (CU 87864, CU 89082, CU 92387) and four specimens from Lower Niger (MNHN 1990-942) of Petrocephalus
sauvagii (Abbreviations: m= male; Std–Dev= standard deviation; Min–Max= minimum–maximum).
Live coloration (Fig. 10A). Body uniformly white-silver with metallic iridescence. Two characteristic
melanin markings are present, sometimes with very weak intensity in large individuals: (1) an irregular round
mark below the anterior base (first to fourth rays) of the dorsal fin; (2) an ovoid blackish mark, often irregular
in shape, centered at the base of the caudal fin and extending onto the upper and lower fleshy lobes of this fin.
The fins themselves (caudal fins and others) are translucent.
Distribution (Fig. 1). Petrocephalus sauvagii is the only species of Petrocephalus known to occur in both
the Congo and Niger basins. There is no record of this species occurring in the Lower Guinea province. The
holotype was collected from "the creeks of the Lower Congo and the tributary streams" without more
Holotype
(m)
Specimens
from Odzala
(n=6)
Specimens from
Lower Niger
(n=4)
Min–Max Mean Std–Dev Min–Max Mean Std–Dev
Standard length (mm) 146.7 109.2–189.0 156.2 33.3 118.7–127.7 122.0 3.9
Head length (mm) 50.3 31.1–51.6 43.6 8.6 31.2–32.9 32.0 0.8
Ratio of standard length (SL):
SL/body height (H) 2.9 2.7–3.4 3.0 0.3 2.5–2.7 2.6 0.1
SL/head length (HL) 3.7 3.5–3.7 3.6 0.1 3.8–3.9 3.8 0.0
SL/pre-dorsal distance (PDD) 1.6 1.5–1.6 1.6 0.1 1.6–1.6 1.6 0.0
SL/pre-anal distance (PAD) 1.6 1.5–1.7 1.6 0.1 1.6–1.7 1.6 0.0
SL/dorsal fin length (DFL) 4.5 4.2–4.7 4.5 0.2 4.1–4.5 4.3 0.2
SL/anal fin length (AFL) 3.6 3.1–3.4 3.3 0.1 3.2–3.3 3.2 0.1
SL/caudal peduncle length (CPL) 6.3 6.1–7.7 7.0 0.8 6.0–6.2 6.1 0.1
SL/mouth width (MW) 11.4 11.2–12.9 11.9 0.6 10.2–12.4 11.7 1.0
Ratio of head length (HL):
HL/snout length (SNL) 6.7 6.3–9.9 8.0 1.5 5.5–6.8 5.9 0.6
HL/mouth width (MW) 3.1 3.1–3.7 3.3 0.2 2.7–3.2 3.1 0.2
HL/eye diameter (ED) 4.6 4.1–4.5 4.3 0.1 4.0–4.2 4.1 0.1
HL/interorbital width (IOW) 3.5 3.5–4.2 3.8 0.3 2.6–2.7 2.7 0.1
HL/head width (HW) 2.1 1.8–2.4 2.1 0.3 1.7–1.9 1.8 0.1
HL/mouth position (MP) 4.9 5.5–7.4 6.6 0.9 4.4–5.4 5.0 0.4
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.7 2.3–3.1 2.6 0.4 2.6–2.8 2.7 0.1
Min–Max Median Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 27 26–30 28 25–25 25
Anal fin branched rays (AR) 34 33–38 35 32–33 32
Number of scales in the lateral line (SLL) 36 38–41 39 37–40 39
Number of scale rows between the anterior
base of the anal fin and the lateral line (SDL)
14 12–16 14 12–14 13
Number of teeth in the upper jaw (TUJ) 26 24–30 26
Number of teeth in the lower jaw (TLJ) 30 30–34 32
LAVOUÉ ET AL.32 · Zootaxa 2600 © 2010 Magnolia Press
precision being given on the exact locality (Boulenger, 1887). In Odzala, we collected P. sauvagii at several
localities along the main course of the Lékoli River and, exclusively at night, in some small tributary creeks
flowing through savannah.
Electric organ discharge (Fig. 10C). EOD recordings are only available for three individuals. Thus,
generalizations about the EOD features of this species must be made with caution. EOD waveforms of all
three individuals are of somewhat short duration for the genus (range = 0.232 – 0.273 msec), but they are,
nevertheless, very similar to EODs of several other Petrocephalus species. Statistics for waveform landmarks
and other EOD measurements for P. sauvagii are provided by Lavoué et al. (2008), who demonstrated
histologically that the electrocytes of this species are type NPp.
Remarks. We noticed some morphological differences between allopatric specimens of P. sauvagii from
the Niger and Congo basins. Specimens from the Niger basin possess fewer anal fin rays (32–33 versus 33–
38), a longer snout (HL/SNL = 5.5–6.8 versus 6.3–9.9) and a greater interorbital width (HL/IOW = 2.6–2.7
versus 3.5–4.2) than Odzala specimens.
Petrocephalus pulsivertens n. sp.
[Odzala field identification and in Lavoué et al (2008): Petrocephalus sp. 9, OTU 9]
Images. Fig. 11A, photo of a live specimen from Odzala and Fig. 11B, photo of the preserved holotype (CU
88085).
Type material. Holotype, CU 88085 (morpho, DNA), male, 114.8 mm SL. Republic of the Congo, small
channel around island in Lékoli River (Congo basin), Odzala National Park, (0.62° N, 14.95° E), V. Mbossi,
J.P. Friel, S. Lavoué & J.P. Sullivan coll., 16 August 2002.
Paratypes. AMNH 251418 (ex CU 88096) (morpho, EOD), male, 99.9 mm SL; CU 88097 (morpho, EOD,
DNA; caudal peduncle dissected by Lavoué et al. (2008) to sample electric organ for histological
examination), sex undet., 95.0 mm SL; AMNH 251419 (ex CU 88098) (morpho, EOD), sex undet., 103.2 mm
SL.
Republic of the Congo, small channel around island in Lékoli River (Congo basin), Odzala National Park,
(0.62° N, 14.95° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., 20 August, 2002. CU 87839 (morpho, EOD,
DNA), male, 87.3 mm SL; CU 89188 (morpho), sex undet., 98.5 mm SL; CU 89188 (morpho, caudal
peduncle dissected by Lavoué et al. (2008) to sample electric organ for histological examination, sex undet.,
103.6 mm SL; CU 89188 (morpho), male, 107.4 mm SL; CU 89188 (morpho), male, 86.1 mm SL.
Republic
of the Congo
, small channel around island in Lékoli River (Congo basin), Odzala National Park, (0.62° N,
14.95° E), V. Mbossi, J.P. Friel, S. Lavoué & J.P. Sullivan coll., 16 August 2002.
Other specimens. We examined five other specimens from Odzala National Park and one from the
Sangha River basin (specimen list provided in the section "additional material examined").
Diagnosis. Petrocephalus pulsivertens n. sp. is distinguished from all other Petrocephalus species in
Central Africa by the following combination of characteristics. Dorsal fin with at least 25 branched rays
(range = 25–27). Anal fin with at least 31 branched rays (range = 31–35). Mouth large (HL/MW
3.7, range
= 3.0–3.7). Fifteen to 21 teeth in the lower jaw; 24–30 teeth in the upper jaw. Eye large (HL/ED
3.5, range =
3.2–3.5). Pigmentation pattern consists of two distinctive melanin markings (black patches): (1) a distinct
ovoid mark below the anterior base of the dorsal fin; and (2) a crescent-like mark, sometimes diffuse, centered
at the base of the caudal fin and extending onto the upper and lower parts of the caudal fin. EOD appears to be
inverted in polarity, with a first main phase that is negative under the standard recording geometry, resulting in
a waveform that is very distinctive in comparison to all known congeners.
Description. Morphometric ratios and meristic data for the holotype and paratypes are presented in Table
9. Petrocephalus pulsivertens n. sp. is a relatively large sized species within the genus Petrocephalus
(maximum SL observed = 114.8 mm, the length of the holotype). Body ovoid, longer than high (2.6
SL/H
2.9, paratype average = 2.7, holotype = 2.8) and laterally compressed. Head length between 3.6 and 3.7 times
in standard length (holotype = 3.7). Eye large (3.2
HL/ED 3.5, paratype average = 3.4, holotype = 3.5).
Snout short (6.1
HL/SNL 7.3, paratype average = 6.5, holotype = 6.8) and round. Mouth large (3.0 HL/
Zootaxa 2600 © 2010 Magnolia Press · 33
PETROCEPHALUS OF ODZALA
FIGURE 11. Petrocephalus pulsivertens n. sp. of the Lékoli River system of Odzala National Park, Republic of the
Congo
. A. Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88085; scale bar = 1.0
cm). C. EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the
other recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted
(head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar =
0.2 msec).
MW 3.7, paratype average = 3.3, holotype = 3.0), sub-terminal, opening just under the anterior half of the
eye. Teeth bicuspid, small and numerous, 15–21 (paratype average = 18, holotype = 21) in a single row in the
upper jaw, 24–30 (paratype average = 28, holotype = 29) in a single row in the lower jaw. Dorsal and anal fins
originate in the posterior half of the body (1.6
SL/PDD 1.7 and 1.7 SL/PAD 1.8, respectively). Pre-
dorsal distance equal to, or slightly greater than, pre-anal distance (1.0
PDD/PAD 1.1). Dorsal fin with 25–
LAVOUÉ ET AL.34 · Zootaxa 2600 © 2010 Magnolia Press
27 branched rays (paratype median = 26, holotype = 26). Anal fin with 31–35 branched rays (paratype median
= 33, holotype = 34). Scales cover the body, except for the head. Lateral line visible and complete with 38–40
pored scales along its length. Caudal peduncle relatively thin (2.1
CPL/CPD 2.3, holotype = 2.2). Twelve
scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation.
Knollenorgan electroreceptors on head clustered into three distinct rosettes.
TABLE 9. Principal morphometric ratios and meristic counts for the holotype (CU 88085) and eight paratypes (CU
88097, CU 87839, CU 89188, AMNH 250932, AMNH 250933) of Petrocephalus pulsivertens n. sp. (Abbreviations: m=
male; Std–Dev= standard deviation; Min–Max= minimum–maximum).
Live coloration (Fig. 11A). Body and head mostly whitish-silvery, but head also exhibits faint metallic
blue-purple iridescence. Dorsum darker than the rest of the body. Melanin patterning consists of two distinct
black marks: (1) a distinct ovoid melanin mark below the anterior base of the dorsal fin on each side of the
Holotype (m) Paratypes (n=8)
Min–Max Mean Std–Dev
Standard length (mm) 114.8 86.1–107.4 97.6 7.7
Head length (mm) 30.9 23.5–30.9 26.6 2.1
Ratio of standard length (SL):
SL/body height (H) 2.8 2.6–2.9 2.7 0.1
SL/head length (HL) 3.7 3.6–3.7 3.7 0.1
SL/pre-dorsal distance (PDD) 1.6 1.6–1.7 1.6 0.0
SL/pre-anal distance (PAD) 1.7 1.7–1.8 1.7 0.0
SL/dorsal fin length (DFL) 4.3 3.9–4.3 4.1 0.1
SL/anal fin length (AFL) 3.2 2.9–3.3 3.1 0.1
SL/caudal peduncle length (CPL) 6.5 6.8–6.1 6.6 0.2
SL/mouth width (MW) 11.1 11.1–13.8 12.2 0.8
Ratio of head length (HL):
HL/snout length (SNL) 6.8 6.1–7.3 6.5 0.4
HL/mouth width (MW) 3.0 3.0–3.7 3.3 0.2
HL/eye diameter (ED) 3.5 3.2–3.5 3.4 0.1
HL/interorbital width (IOW) 3.1 2.9–3.4 3.1 0.2
HL/head width (HW) 1.8 1.8–2.0 1.9 0.1
HL/mouth position (MP) 3.3 3.0–3.5 3.3 0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 2.2 2.1–2.3 2.1 0.1
Min–Max Median
Meristic counts:
Dorsal fin branched rays (DR) 26 25–27 26
Anal fin branched rays (AR) 34 31–35 33
Number of scales in the lateral line (SLL) 39 38–40 39
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
14 13–15 14
Number of teeth in the upper jaw (TUJ) 21 15–21 18
Number of teeth in the lower jaw (TLJ) 29 24–30 28
Zootaxa 2600 © 2010 Magnolia Press · 35
PETROCEPHALUS OF ODZALA
body and (2) a crescent-like melanin mark, sometimes diffuse, centered at the base of the caudal fin on each
side and extending onto the upper and lower parts of the caudal fin. No black mark is present at the base of the
pectoral fins. The fins themselves are mostly translucent, with the dorsal and caudal fins sometimes turning
slightly yellow after formaldehyde preservation.
Distribution (Fig. 1). Endemic to the Congo River basin. We collected P. pulsivertens n. sp. along the
main course of the Lékoli River. This species seemed to be absent from the small tributary creeks flowing
through forest or savannah when we surveyed Odzala National Park. Elsewhere, P. pulsivertens n. sp. occurs
in the vicinities of Brazzaville (i.e., the Pool Malebo), the Dja River (Cameroon) and the Dzangha-Sangha
region (Sangha River basin, Central African Republic) (pers. obs.), although no EOD recordings have been
made of this species outside Odzala.
Electric organ discharge (Fig. 11C). The EOD waveform of P. pulsivertens n. sp., which is known only
from our recordings in Odzala, resembles an inverted-polarity version of the "typical" Petrocephalus EOD.
That is, the temporal sequence of electrocyte face firing known for all other Petrocephalus (i.e., firing of the
posterior electrocyte face preceding firing of the anterior electrocyte face) appears to be reversed in P.
pulsivertens. At high gain, however, one can see that the very first event in the EOD is a minute head-positive
deflection (for an example see Fig. 3D of Lavoué et al., 2008). This waveform feature is consistent with
current from the stalks of the posterior electrocyte face (and possibly early current during the beginning of
posterior face firing itself) slightly preceding anterior face firing. Despite the waveform inversion, histological
examination of electrocytes of P. pulsivertens n. sp. reveals them to be type "NPp," the character state also
shared by all other Petrocephalus species investigated to date. We suspect that part of the mechanism
underlying the reversed ordering of major peaks in the EOD of P. pulsivertens n. sp. might involve changes in
firing threshold for one or both electrocyte faces (as proposed in Lavoué et al., 2008). This interesting
example of waveform inversion in Petrocephalus reminds us that careful attention must be paid to the
geometry of electrodes during EOD recordings from unknown mormyrid faunas. Given its inverted-polarity
appearance, the EOD of P. pulsivertens n. sp. is immediately recognizable as distinct from those of all other
congeners. Based on a threshold of 1.5% of peak-peak amplitude (and at ambient recording temperatures), the
duration of the EOD of P. pulsivertens n. sp. ranges from 0.270 to 0.418 msec, falling in the range of many
"typical" Petrocephalus EODs. Statistics for waveform landmarks and other EOD measurements are provided
by Lavoué et al. (2008).
Etymology. From the Latin "pulsus," impulse, beating; and from "vertere," to turn, exchange. The name
describes the unusual EOD waveform of P. pulsivertens n. sp. The inverted appearance of this species’ EOD
is unique among all Petrocephalus recorded to date.
Petrocephalus grandoculis Boulenger, 1920
Petrocephalus grandoculis Boulenger (1920): 10.
[Odzala field identification: Petrocephalus sp. 10, OTU 10]
Images. Fig. 12A, photo of a live specimen from Odzala, Fig.12B, photo of a preserved specimen from
Odzala and Fig. 14, drawing of one syntype from Boulenger (1920), p. 10. Photo of two syntypes in Harder
(2000).
Type material. Syntypes, BMNH 1919.9.10.16–17 [examined] and MRAC 7158, 7167 [not examined].
Leopoldville (Kinshasa), Zaire (Democratic
Republic of the Congo)[estimated 4.25° S, 15.33° E].
Other specimens. We also examined two specimens from Odzala National Park (specimen list provided
in the section “additional material examined”).
Diagnosis. The following diagnosis is based on all examined specimens of P. grandoculis, regardless their
geographic origins. Petrocephalus grandoculis is distinguished from all other Petrocephalus species in
Central Africa by the following combination of characteristics. Very small mouth (5.2
HL/MW 6.1). Eight
to 11 teeth in the lower jaw. Upper jaw with 18–22 teeth. Eye large (2.8
HL/ED 3.2). Snout short (6.5
HL/SNL
10.7). Dorsal fin with 24–26 branched rays. Anal fin with 30–33 branched rays. Pigmentation
LAVOUÉ ET AL.36 · Zootaxa 2600 © 2010 Magnolia Press
pattern consists of two melanin markings (black patches): (1) a distinct, although generally weak, round black
mark on each side of the body below the anterior base of the dorsal fin (first to fifth rays); and (2) a crescent-
like mark at the base of the caudal fin on each side, not extending onto the rayed portions of the upper and
lower caudal fin lobes. EOD of normal polarity.
FIGURE 12. Petrocephalus grandoculis of the Lékoli River system of Odzala National Park, Republic of the Congo. A.
Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD
waveform. One EOD was arbitrarily selected from the only individual of this species recorded in Odzala, an obvious
male. The EOD is shown here head-positive up (scale bar = 0.2 msec).
Zootaxa 2600 © 2010 Magnolia Press · 37
PETROCEPHALUS OF ODZALA
TABLE 10. Principal morphometric ratios and meristic counts for the two syntypes (BMNH 1919.9.10.16-17) and two
specimens from Odzala (CU 88119, CU 92385) of Petrocephalus grandoculis Boulenger, 1920 and the holotype (CU
92389) of Petrocephalus mbossou n. sp., (Abbreviations: o= sex category "other" [i.e., not an obvious mature male, but
rather a female or immature male]; Min–Max= minimum–maximum).
Description. Table 10 provides morphometric ratios and meristic data for the two Kinshasa syntypes and,
separately, for the two non-type specimens from Odzala National Park. The following description applies to
the two Odzala specimens, with separate reference to the two syntypes. Petrocephalus grandoculis is a
medium-sized species within the genus Petrocephalus (maximum SL observed = 97.8 mm). Body ovoid,
longer than high (2.5
SL/H 2.7, syntypes = 3.0–3.1) and laterally compressed. Head length 3.8–4.2 times
in standard length (syntypes = 3.9–4.1). Eye quite large (2.8
HL/ED 3.1, syntypes = 3.1–3.2). Snout short
(6.5
HL/SNL 10.7, syntypes = 6.5–6.7) and round. Mouth very small (5.2 HL/MW 5.9, syntypes =
P. grandoculis
Syntypes (n=2)
P. grandoculis
Odzala specimens (n=2)
P. mbossou n. sp.
Holotype (o)
Min–Max Min–Max
Standard length (mm) 74.0–76.0 88.0–97.8 127.1
Head length (mm) 18.4–19.0 23.0–23.5 36.9
Ratio of standard length (SL):
SL/body height (H) 3.0–3.1 2.5–2.7 3.0
SL/head length (HL) 3.9–4.1 3.8–4.2 3.4
SL/pre-dorsal distance (PDD) 1.6–1.6 1.6–1.6 1.7
SL/pre-anal distance (PAD) 1.7–1.8 1.7–1.7 1.6
SL/dorsal fin length (DFL) 4.2–4.6 4.0–4.1 4.4
SL/anal fin length (AFL) 3.3–3.3 3.1–3.3 4.3
SL/caudal peduncle length (CPL) 5.8–6.1 5.3–6.7 5.2
SL/mouth width (MW) 23.6–23.6 21.7–22.4 16.2
Ratio of head length (HL):
HL/snout length (SNL) 6.5–6.7 6.5–10.7 5.4
HL/mouth width (MW) 5.7–6.1 5.2–5.9 4.7
HL/eye diameter (ED) 3.1–3.2 2.8–3.1 3.7
HL/interorbital width (IOW) 3.4–3.7 3.2–3.8 4.3
HL/head width (HW) 2.1–2.2 1.8–1.9 2.2
HL/mouth position (MP) 3.7–4.0 4.5–5.0 2.8
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD) 3.0–3.0 2.2–3.0 2.9
Min–Max Min–Max
Meristic counts:
Dorsal fin branched rays (DR) 24–26 25–26 24
Anal fin branched rays (AR) 30–31 32–33 26
Number of scales in the lateral line (SLL) 38–38 37–39 37
Number of scale rows between the anterior base of
the anal fin and the lateral line (SDL)
15–15 13–15 11
Number of teeth in the upper jaw (TUJ) 10–11 8–8 12
Number of teeth in the lower jaw (TLJ) 19–20 18–22 14
LAVOUÉ ET AL.38 · Zootaxa 2600 © 2010 Magnolia Press
5.7–6.1), sub-terminal, opening under the anterior half of the eye. Teeth small and bicuspid, only eight
(syntypes = 10 or 11) in a single row in the upper jaw, 18–22 (syntypes = 19 or 20) in a single row in the lower
jaw. Dorsal and anal fins originate in the posterior half of the body [SL/PDD = 1.6 and SL/PAD = 1.7
(syntypes = 1.7–1.8), respectively]. Pre-dorsal distance slightly greater than pre-anal distance (1.0
PDD/
PAD
1.1). Dorsal fin with 25–26 branched rays (syntypes = 24–26). Anal fin with 32 or 33 branched rays
(syntypes = 30 or 31). Scales cover the body, except for the head. Lateral line visible and complete with 37–39
(syntypes = 38) pored scales along its length. Caudal peduncle relatively thin (2.2
CPL/CPD 3.0, syntypes
= 3.0). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin
fixation. The numerous Knollenorgan electroreceptors on the head are clearly organized into two visible
rosettes (Augenrosette and Nackenrosette). In our examination of specimens, we were uncertain about the
definitive presence of the third rosette, the Kehlrosette, as this structure did not appear to us to be as distinct as
it is in other species (e.g., P. binotatus). However, more definitive recent analysis using toluidine blue staining
of the skin now suggests that the Kehlrosette is present, but smaller and harder to discern than in other
Petrocephalus (M. Hollmann and B. A. Carlson, unpub. obs.).
Live coloration (Fig. 12A). Body mostly white-silver. Dorsum slightly darker than the rest of the body.
Pigmentation pattern consists of two melanin markings: (1) a distinct, but weak, round black mark below the
anterior base of the dorsal fin (first to fifth rays); and (2) a crescent-shaped mark at the base of the caudal fin,
which does not extend onto the rayed portions of the upper and lower caudal fin lobes. No black mark is
present at the base of pectoral fins. The fins themselves are translucent.
Distribution (Fig. 1). Endemic to the Congo basin. The type locality is situated on the Lower Congo
River at Kinshasa. In Odzala, we collected only two specimens of P. grandoculis from the main channel of the
Lékoli River.
Electric organ discharge (Fig. 12C). EODs have only been recorded from one individual of P.
grandoculis, which was collected in Odzala National Park. The EOD duration for this individual (0.380 msec,
based on 1.5% deviations from baseline) and the general appearance of the waveform are typical for
Petrocephalus. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et
al. (2008). Electrocyte anatomy is unknown, although it is expected to be type "NPp" as deduced from the
EOD waveform.
Petrocephalus mbossou n. sp.
[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 11, OTU 11]
Images. Fig. 13A, photo of the live holotype (CU 92389) and Fig. 13B, photo of the preserved holotype.
Type material. Holotype, CU 92389 (morpho, EOD, DNA), sex undet., 127.2 mm SL. Republic of the
Congo
, Cuvette-Ouest, Lékoli River (Congo basin), small branch of the Lékoli River, only ca. 300 meters
long before it re-enters into the main channel of the Lékoli (0.62° N, 14.91° E), M.E. Arnegard, V. Mbossi, E.
Kinzonzi, S. Lavoué, V. Mamonekene & P.B. McIntyre coll., June 2006.
Diagnosis. Petrocephalus mbossou n. sp. is distinguished from all other Petrocephalus species in Central
Africa by the following combination of characteristics. Dorsal fin with 24 branched rays. Anal fin with 26
branched rays. Mouth inferior and small (HL/MW = 4.7) with 12 teeth in a single row in the upper jaw and 14
teeth in a single row in the lower jaw. Distance from the anterior extremity of the snout to the corner of the
mouth (i.e., MP) only 2.8 times in head length. Weak pigmentation pattern with the presence of two black
markings on each side of the body: (1) an irregular patch below the anterior base of the dorsal fin (first ray to
the sixth/seventh rays); (2) an irregularly-shaped mark centered at the base of the caudal fin that does not
extend onto the rayed portions of the upper and lower caudal fin lobes. EOD of normal polarity (i.e., first
major phase head-positive) and very brief duration. Unlike any other Petrocephalus species, the second head-
positive phase in the EOD (P3) is larger in amplitude than the first head positive phase (P1).
Zootaxa 2600 © 2010 Magnolia Press · 39
PETROCEPHALUS OF ODZALA
FIGURE 13. Petrocephalus mbossou n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo.
A. Live photograph of the holotype (CU 92389; no scale). B. Photograph of the preserved holotype (scale bar = 1.0 cm).
C. EOD waveform of the holotype. One EOD was arbitrarily selected from all recordings made of this individual. The
selected EOD is shown here head-positive up (scale bar = 0.2 msec).
Description. This description is based on data collected solely from the holotype, which is the only
specimen of this species collected to date. Table 10 provides morphometric ratios and meristic data for the
holotype. Petrocephalus mbossou n. sp. is a large-sized species within the genus Petrocephalus (SL = 127.1
mm). Body ovoid, longer than high (SL/H = 3.0) and laterally compressed. Head length 3.4 times in standard
length. Eye large (HL/ED = 3.7). Snout short (HL/SNL = 5.4) and round. Mouth small (HL/MW = 4.7),
opening ventrally under the posterior half of the eye. Teeth small and bicuspid, 12 in a single row in the upper
LAVOUÉ ET AL.40 · Zootaxa 2600 © 2010 Magnolia Press
jaw, 14 in a single row in the lower jaw. Both the dorsal and anal fins originate in the posterior half of the body
(SL/PDD = 1.7 and SL/PAD = 1.6, respectively). The pre-dorsal distance is slightly greater than the pre-anal
distance. Dorsal fin with 24 branched rays. Anal fin with 26 branched rays. Scales cover the body, except for
the head. Lateral line visible and complete with 37 pored scales along its length. Caudal peduncle relatively
thin (CPL/CPD = 2.9) with twelve circumpeduncular scales. Skin on head thick, turning opaque with formalin
fixation and containing numerous Knollenorgan electroreceptors organized into only two rosettes (the
Nackenrosette and the Kehlrosette). The Augenrosette appears to be absent.
Live coloration (Fig. 13A). Body mostly white-silver. Dorsum slightly darker than the rest of the body.
Pigmentation pattern consists of two distinct black markings: (1) a black patch of irregular shape below the
anterior base of the dorsal fin (first ray to the sixth or seventh ray); (2) an irregularly-shaped mark centered at
the base of the caudal fin that does not extend onto the rayed portions of the upper and lower caudal fin lobes.
The fins themselves are translucent.
FIGURE 14. Historical illustrations of Petrocephalus species described from Congo or Lower Guinea that occur in
Odzala. The drawings were reproduced from the following sources: Petrocephalus binotatus from Pellegrin (1928);
Petrocephalus balayi from Boulenger (1909–1916); Petrocephalus microphthalmus from Poll (1967); Petrocephalus
christyi from Boulenger (1920); Petrocephalus sauvagii from Boulenger (1909–1916); and Petrocephalus grandoculis
from Boulenger (1920).
Zootaxa 2600 © 2010 Magnolia Press · 41
PETROCEPHALUS OF ODZALA
Distribution (Fig. 1). Endemic to the Congo River basin. The single known specimen of this species was
collected in a fish trap, which we had baited with worms and set at night in the main channel of the Lékoli
River on the last day of our second trip.
Electric organ discharge (Fig. 13C). EOD recordings are only available for a single individual (the
holotype), so the following description of EOD features is in need of elaboration based on additional
recordings. In this single individual of P. mbossou n. sp., EOD duration is very brief (0.144 msec), and the
peak spectral frequency is unusually high (22.11 kHz), compared to other Petrocephalus species. In fact,
duration and peak spectral frequency of this EOD recording fall outside the range observed for all other
Petrocephalus individuals/species recorded in Odzala National Park (Lavoué et al., 2008). Like EODs of P.
christyi, the EOD of the holotype of P. mbossou n. sp. possesses a prominent head-negative, fourth peak (P4),
the amplitude of which is 5.7% of the waveform’s total peak-to-peak swing. However, unlike the EOD of P.
christyi (as well those of all other Petrocephalus species from Odzala), the second head-positive peak (P3) is
larger than the first head-positive peak (P1). Electrocyte anatomy is presumed to be of type "NPp" based on
the EOD waveform.
Etymology. The specific epithet is the name given to Petrocephalus locally in the Lingala language.
Speakers of Lingala recognize Petrocephalus as a natural group, which they call "mbossou."
Remarks. We opted to describe P. mbossou as a new species based only on the holotype for the following
reasons. This individual specimen has a unique cytb haplotype and does not belong to any putative species
(consisting of two or more specimens) of Petrocephalus in our molecular phylogenetic tree, and its body form
and EOD are outside the ranges observed for all other Odzala Petrocephalus specimens, as well as all type
material for Petrocephalus species of the Congo and Lower Guinea provinces. In taxonomic investigations of
fish faunas from more accessible regions of Africa, it is normally (and reasonably) expected that investigators
collect multiple specimens before describing a new species. However, given the remote location of Odzala
National Park it may be some time before additional specimens become available. This fact and this species’
distinctive morphology, EODs and DNA justify describing P. mbossou n. sp. at this time with only a single
specimen.
Discussion
Our method for clarifying the taxonomy and systematics of weakly electric mormyrid fishes combines three
lines of evidence: morphological, electrophysiological and genetic. Application of this integrative and
sensitive approach to our collections in Odzala National Park allows us to recognize eleven species of
Petrocephalus co-occurring in this small region of the Congo River basin (Lavoué et al., 2008). Comparisons
of these collections with type material for all Petrocephalus species described thus far from the Congo and
Lower Guinea provinces lead us to describe five of the eleven Odzala taxa as new Petrocephalus species.
Electric organ discharge (EOD) waveform variation (among species and between sexes) is generally
smaller in the genus Petrocephalus, and therefore in the subfamily Petrocephalinae, than it is in the subfamily
Mormyrinae (Arnegard et al., 2005; Arnegard & Hopkins, 2003; Bratton & Kramer, 1988; Crawford &
Hopkins, 1989; Feulner et al., 2006; Hopkins, 1981; Kramer, 1997; Lavoué et al., 2008; Sullivan et al., 2002;
Sullivan et al., 2000). Although slight EOD differences are usually detectable statistically among
Petrocephalus species (Kramer & van der Bank, 2000; Lavoué et al., 2008; Moritz et al., 2009), they are of
little practical use for the taxonomic discrimination of most Petrocephalus species. In this regard, P.
pulsivertens of the Odzala assemblage is a notable exception, expressing the most divergent EOD waveform
known among all Petrocephalus species (Lavoué et al., 2008). Despite the EOD waveform similarities among
most other Petrocephalus species (i.e., on the motor side of electric signaling), we found interesting variation
in the patterns with which Knollenorgan electroreceptors are distributed on the heads of species in this genus
(Harder, 1968; 2000). These external anatomical differences in electroreceptor distribution raise the
possibility that related variation exists in the sensory pathways underlying electrical communication in
Petrocephalus.
LAVOUÉ ET AL.42 · Zootaxa 2600 © 2010 Magnolia Press
FIGURE 15. Petrocephalus phylogeny (17 species, 59 specimens, 53 haplotypes) estimated by maximum likelihood
using complete cytochrome b sequences (dataset #1; see text). Gnathonemus petersii, Mormyrops nigricans and
Myomyrus macrops were used as outgroups to root the tree. Numbers at internal branches are bootstrap proportions (in
%) shown only when they exceed 50%. Due to space limitations, support values are not shown for intraspecific
relationships. Black vertical bars to the right of the tree indicate specimens sampled from Odzala. White bars (with the
river basins from which the specimens were collected) indicate Petrocephalus individuals from other regions of Africa.
The scale bar corresponds to 0.04 substitutions per site.
Molecular markers, such as the mitochondrial cytb gene used in our study, appear to be particularly
promising for the elucidation of species boundaries in Petrocephalus. Deep genetic divisions among species
Zootaxa 2600 © 2010 Magnolia Press · 43
PETROCEPHALUS OF ODZALA
and exclusive monophyly of such taxa appear to be common patterns in the phylogeny of the Petrocephalinae
as estimated by cytb (Lavoué et al., 2008). Given results of our cytb sequencing and analysis (Fig. 15), the
eleven species of Petrocephalus in Odzala National Park appear to be good biological species that are
reproductively isolated from one another. However, a practical difficulty associated with the molecular
component of our integrative taxonomic approach is its ineffectiveness for immediately identifying new
specimens in the field. When applied together, the morphological and electrophysiological components of our
approach can provide rapid and reliable field identifications (see our Key to the Petrocephalus species of
Odzala, below). The single factor that most limits progress on the taxonomy and systematics of Petrocephalus
is the lack of field collections from vast areas of the Congo River basin and several other regions of Africa.
We have updated our cytb-based phylogenetic hypothesis for this genus by adding two new taxa for the
present study: Petrocephalus bovei and Petrocephalus catostoma (Fig. 15). The first of these, P. bovei, was
described from the Nile River, although it is thought to be widely distributed throughout the Nilo-Sudanian
region including the Niger and Nile Rivers, the Lake Chad basin and most of the smaller coastal drainages
extending from the Senegal River south along the Gulf of Guinea to the Cross River in Cameroon.
Petrocephalus catostoma was described from the Rovuma River at the border between Tanzania and
Mozambique (Günther, 1866; Whitehead & Greenwood, 1959). This species is widely distributed in East
Africa from the Zambezi River system in southern Africa to the Tana River in Kenya, including the basins of
Lakes Victoria, Malawi and Tanganyika. Our molecular analysis clearly shows that none of the species of
Petrocephalus found in Odzala are closely related to P. bovei or P. catostoma (Fig. 15).
Before this present work, eleven species and sub-species of Petrocephalus were recorded from the entire
Congo River system (Boulenger, 1909–1916; Daget et al., 1984; Harder, 2000; Eschmeyer & Fricke, 2010).
Our results now support the recognition of 16 Petrocephalus species and sub-species in the Congo basin, with
eleven species co-occurring in a single, small river system, the Lékoli, located in the basin’s northwestern
corner. The immense size of the Congo River basin, the poor sampling of many regions within it and the
difficulty of identifying Petrocephalus species from preserved material virtually guarantees that this number
underestimates the true diversity of Congo basin Petrocephalus.
Additional taxonomic remarks
While examining the type specimens of all Petrocephalus species known from the Congo and Lower Guinea
provinces, we noted that Petrocephalus guttatus Fowler, 1936 does not exhibit the characteristic combination
of traits diagnostic for this genus. The holotype of P. guttatus [from the Kribi Creeks, Lower Guinea region
(Fowler, 1936)] lacks all of the following character states typical of Petrocephalus: nares closely apposed and
directly in front of the eye; all teeth of the lower and upper jaws bicuspid and of the same size; mouth inferior,
rictus under eye; Knollenorgan electroreceptors organized into rosettes (Harder, 1968; 2000). Therefore, we
provisionally re-assign Petrocephalus guttatus to the genus Pollimyrus based on the apparent morphological
similarity between Petrocephalus guttatus and Pollimyrus isidori (Valenciennes in Cuvier and Valenciennes,
1847).
The generic assignment of Petrocephalus hutereaui (Boulenger, 1913) is also dubious and represents
another difficult case. Boulenger (1913) described this species from a single specimen of small size collected
in the Upper Congo at Dungu (Fig. 1), but he treated this species as a representative of the genus Marcusenius.
Our examination of the holotype does not allow us to conclude unambiguously as to which genus this
specimen should be assigned. The small size and poor condition of the holotype renders difficult the
assessment of diagnostic characters such as the relative position of the nares or the presence/absence of
Knollenorgan rosettes. The taxonomic statuses of other doubtful Petrocephalus species described from the
Congo basin and the Lower Guinea province were previously clarified: Petrocephalus affinis Sauvage, 1879
is considered to be a synonym of Stomatorhinus walkeri (Günther, 1867); Petrocephalus marchei Sauvage,
1879 a synonym of Ivindomyrus marchei; Petrocephalus vanderbilti Fowler, 1936 a synonym of Pollimyrus
isidori; and Petrocephalus anterodorsalis David and Poll, 1937 a synonym of Pollimyrus tumifrons
(Boulenger, 1902).
LAVOUÉ ET AL.44 · Zootaxa 2600 © 2010 Magnolia Press
Comments on the identification of Petrocephalus in the Congo and Lower Guinea provinces
During our efforts to place the Petrocephalus of Congo and Lower Guinea into discrete morphological
categories, we found it convenient to initially divide specimens into two groups depending on the number of
branched rays in the dorsal fin. The first group includes species with generally fewer than 19 (rarely 19 or 20)
dorsal fin branched rays [i.e., Petrocephalus catostoma congicus David and Poll, 1937, P. catostoma
haullevillii, P. microphthalmus, P. schoutedeni and Petrocephalus squalostoma (Boulenger, 1915)]. The
second group contains larger species that almost always exhibit 20 or more branched rays in the dorsal fin [P.
balayi, P. binotatus, P. christyi, P. mbossou n. sp., P. odzalaensis n. sp., P. pulsivertens n. sp., P. sauvagii, P.
valentini n. sp., P. zakoni n. sp., Petrocephalus simus Sauvage, 1879 and Petrocephalus sullivani Lavoué,
Hopkins and Kamdem Toham, 2004].
In the first morpho-group, P. catostoma congicus, P. catostoma haullevillii, P. schoutedeni and P.
squalostoma are so far known only from type material, whereas P. microphthalmus has been collected
throughout a wide distribution. Petrocephalus catostoma congicus is easly distinguishable morphologically
from the others within this group. The differences between P. microphthalmus, P. schoutedeni and P.
catostoma haullevillii need to be further studied with additional collections of P. schoutedeni and P. catostoma
haullevillii that are suitable for integrative comparisons of morphology, EODs and genetic markers.
The second morpho-group includes eleven described species and probably several others that remain
undescribed. Prior to our work, the taxonomic confusion surrounding species identification in this group was
largely due to the use of P. christyi and P. simus as "wastebasket" species (Bigorne & Paugy, 1991; Lavoué et
al., 2004). Specimens were erroneously assigned to these taxa without recognizing characters that now help
diagnose species within the second morpho-group of Petrocephalus (e.g., wide mouths in P. sauvagii and P.
balayi, large eyes in P. grandoculis and distinctive melanin markings in P. zakoni n. sp., among other
characters). For instance, taxonomists tended to indiscriminately assign specimens with a black sub-dorsal
patch to P. christyi, and specimens without this characteristic melanin marking to P. simus, without regard to
other aspects of morphological variation (David & Poll, 1937; Poll, 1939; 1967). Attention to EODs and
genetic variation, in addition to morphology, has helped to clarify the formerly cryptic taxonomic variation
within these once wastebasket species. Furthermore, the integrative taxonomic approach has also facilitated
identification of the subtle, but diagnostic morphological traits that distinguish species in this second morpho-
group of Petrocephalus.
Two species in the second group are immediately recognizable by their extremely wide mouths and
square-shaped head profiles when viewed from below (Fig. 6 and 10): P. sauvagii and P. balayi. Given these
features and other distinctive aspects of overall morphology, both species are easy to identify among all other
known Petrocephalus species of the Congo River basin. Furthermore, they can be distinguished from one
another based on number of dorsal fin branched rays, number of teeth in the upper jaw and general melanin
patterning (Fig. 6 and 10). Petrocephalus sauvagii and P. balayi also seem to be adapted to different
ecological niches. Petrocephalus sauvagii occurs in the main channels of moderate to large rivers, while P.
balayi is typically collected from small tributary creeks flowing through the forest. Of the last nine species in
the second morpho-group, the geographical origins of specimens along with a combination of morphological
characters, features of EOD waveforms and molecular data allow us to easily distinguish each species. As an
example, P. pulsivertens n. sp. is readily identified among other species in this group by its relatively wide
mouth, presence of more teeth in both jaws, more branched rays in the dorsal and anal fins, unique
pigmentation pattern and "inverted" EOD waveform, in addition to other characters.
Attention to the two operational morpho-groups of Petrocephalus that we distinguish by number of
branched dorsal fin rays facilitates the further taxonomic discrimination of individuals within this genus.
However, because our molecular phylogenetic analysis has so far only included one species from the first
morpho-group (with DR < 19), P. microphthalmus
, we cannot yet evaluate to what degree these operational
groups correspond to natural spe