A New Stomatorhinus (Osteoglossomorpha: Mormyridae) From The Ivindo River, Gabon, West Central Africa

Abstract

Stomatorhinus ivindoensis n. sp. is described from the basin of the Ivindo River, a tributary of the Ogooué River, in Gabon, West Central Africa. This species is characterized by its very small size which is not known to exceed 56 mm standard length. It is distinguished from S. fuliginosus from the Congo basin, the only described Stomatorhinus for which all members of the type series are within the size range of S. ivindoensis, by a smaller caudal peduncle depth to length ratio, a nar- rower head, a greater number of lateral line scales with visible tubes and pores and by rounded cau- dal fin lobes. It is distinguished from the similar S. polli, also from the Congo basin, by a longer snout, a smaller eye and a greater interorbital width relative to head length. It is distinguished from S. walkeri, the only other species described from the Ogooué River basin, by its smaller size, smaller snout to pectoral fin distance (relative to standard length) and by its reduced numbers of pectoral rays, vertebrae, and lateral line scales with visible tubes and pores. Stomatorhinus ivin- doensis is endemic to the Ivindo River basin of Gabon and is allopatrically distributed with respect to S. walkeri which, although found elsewhere in the Ogooué River basin, has never been recorded from the Ivindo River. Stomatorhinus ivindoensis may be the smallest species of mormyrid fish yet described.

Full text

847
Accepted by L. Page: 25 Jan. 2005; published: 1 Feb. 2005 1
ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN 1175-5334 (online edition)
Copyright © 2005 Magnolia Press
Zootaxa 847: 1–23 (2004)
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A new Stomatorhinus (Osteoglossomorpha: Mormyridae) from the
Ivindo River, Gabon, West Central Africa
JOHN P. SULLIVAN1,2 & CARL D. HOPKINS1
1Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853 USA 2Department of Ich-
thyology, American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024 USA, e-
mail: js151@cornell.edu and cdh8@cornell.edu
Abstract
Stomatorhinus ivindoensis n. sp. is described from the basin of the Ivindo River, a tributary of the
Ogooué River, in Gabon, West Central Africa. This species is characterized by its very small size
which is not known to exceed 56 mm standard length. It is distinguished from S. fuliginosus from
the Congo basin, the only described Stomatorhinus for which all members of the type series are
within the size range of S. ivindoensis, by a smaller caudal peduncle depth to length ratio, a nar-
rower head, a greater number of lateral line scales with visible tubes and pores and by rounded cau-
dal fin lobes. It is distinguished from the similar S. polli, also from the Congo basin, by a longer
snout, a smaller eye and a greater interorbital width relative to head length. It is distinguished from
S. walkeri, the only other species described from the Ogooué River basin, by its smaller size,
smaller snout to pectoral fin distance (relative to standard length) and by its reduced numbers of
pectoral rays, vertebrae, and lateral line scales with visible tubes and pores. Stomatorhinus ivin-
doensis is endemic to the Ivindo River basin of Gabon and is allopatrically distributed with respect
to S. walkeri which, although found elsewhere in the Ogooué River basin, has never been recorded
from the Ivindo River. Stomatorhinus ivindoensis may be the smallest species of mormyrid fish yet
described.
Résumé
Stomatorhinus ivindoensis n. sp. est décrite de la rivière Ivindo, un affluent du fleuve Ogooué, au
Gabon, Afrique Centrale. Cette espèce est caractérisée par sa très petite taille, qui ne dépasse pas 56
mm en longueur standard. Elle se distingue de S. fuliginosus du bassin du Congo, la seule espèce de
Stomatorhinus décrite dont l’intervalle de taille des spécimens types est compris dans celui de S.
ivindoensis, par un rapport largeur sur longueur du pédoncule caudal plus petit, une tête plus étroite,
un nombre d’écailles percées le long de la ligne latérale plus grand et une nageoire caudale aux
lobes arrondies. Elle se distingue de S. polli, une autre espèce similaire du bassin du Congo, par un
museau plus long, un oeil plus petit, et une distance interorbitale plus grande par rapport à la
longueur de la tête. Elle se distingue de S. walkeri, la seule autre espèce de Stomatorhinus décrite du

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ZOOTAXA bassin de l’Ogooué, par une taille plus petite, une distance entre le museau et la nageoire pectorale
(par rapport à la longueur standard) plus petite et par un nombre réduit de rayons aux nageoires pec-
torales, ainsi qu’un nombre réduit de vertèbres et d’écailles percées le long de la ligne latérale. S.
ivindoensis est endémique du bassin de l’Ivindo au Gabon et est allopatriquement distribuée avec S.
walkeri. Quoique cette dernière espèce se rencontre ailleurs dans le bassin de l’Ogooué, elle n’a
jamais été collectée dans le bassin de l’Ivindo. S. ivindoensis est, possiblement, la plus petite espèce
décrite chez les Mormyridae.
Key words: new species, systematics, taxonomy, freshwater fishes, electric fishes, mormyrid, elec-
tric organ discharge
Introduction
Stomatorhinus Boulenger 1898 is a genus of small mormyrid weakly electric fishes from
African freshwaters that is diagnosed by having widely separated nares with the posterior
nares located close to the mouth. In all other mormyrid genera the posterior nares are
remote from the mouth. A second putative synapomorphy for the genus comes from the
study of neuroanatomy: the electrosensory lateral line lobe has two distinct zones on each
side of the midline in all assayed species of Stomatorhinus (7 of 12) in contrast to the three
distinct zones found in all other mormyrid species examined to date (Bell & Russell 1978;
McNamara, Denizot and Hopkins in press).
Twelve species of Stomatorhinus are regarded as valid (Gosse 1984). Ten of these are
endemic to the Congo River basin; an eleventh is found in both the lower Congo and the
coastal Chiloango River, just north of the Congo River mouth. Stomatorhinus walkeri
(Günther 1867), from the Ogooué and Kouilou-Nairi river basins, is the type species of the
genus and the only species described from a region remote from the Congo basin to date.
Here we describe a new species of Stomatorhinus known only from the Ivindo River basin
in Gabon. Although the Ivindo is a large tributary of the Ogooué, there are no records of S.
walkeri from it. Adults of the Ivindo basin Stomatorhinus species are significantly smaller
than adults of S. walkeri and differ in body proportions, counts and coloration. Harder
(2000) assigned these Ivindo basin Stomatorhinus specimens to S. fuliginosus Poll 1941, a
species described from the Congo basin to which they are more similar in counts, measure-
ments and overall size than they are to S. walkeri. Here we show that the Stomatorhinus
from the Ivindo River basin is distinct from S. fuliginosus, S. walkeri and other described
Stomatorhinus and recognize it as a new species.
Materials and Methods
Over 500 specimens in 54 lots of the new species were examined as were the complete or
partial type series of 10 of the 12 valid species of Stomatorhinus. For S. patrizii Vin-

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ciguerra 1928 and S. schoutedeni Poll 1945, measurements and illustrations in the litera-
ture were consulted. Institutional abbreviations follow Leviton et al. (1985).
Morphometric and meristic measurements follow Boden et al. (1997). We took point-
to-point measurements to the nearest 0.1 mm with digital needle-point calipers. We con-
ducted a principal components analysis on 24 log-transformed morphometric measures
taken from specimens of the new species and five others using the software Aabel
(vers.1.5.5, Gigawiz Ltd. Co., 2003). We plotted specimens’ scores on principal compo-
nents two and three to evaluate the degree of size-independent morphometric distinctness
between the new species and the others. Radiographs of specimens were taken at the
AMNH and the ANSP. Vertebral counts do not include the urostyle. We counted circumpe-
duncular scales at the narrowest portion of the caudal peduncle. In all Stomatorhinus spe-
cies, the first pterygiophore of both the dorsal and anal fin are associated with one, two, or
sometimes three simple (unsegmented) rays. Usually, only one of these is substantial
enough to be visible without the aid of radiographs. Therefore dorsal and anal fin ray
counts incorporate only a single first, simple ray and reflect the number of pterygiophores.
Morphometric abbreviations used in text are SL: standard length, HL: head length mea-
sured from tip of snout to posterior margin of opercular membrane.
We recorded electric organ discharges (EODs) in 5 to 20 liter plastic tanks with the
fish immersed in 23 to 28°C water from the capture site. We used silver-chloride-coated
silver wire electrodes mounted at either end of the tank with a ground electrode in the cen-
ter. The electrodes were connected to an AC-coupled differential amplifier with a band-
width of 0.1 to 50 kHz. Individuals collected post 1985 were recorded digitally with an
IOTECH Daqbook 200 (16 bits, variable number of points, 100 kHz sampling rate), or an
IOTECH Wavebook (12 bits, variable number of points, sampling rate to 500 kHz).
Records made prior to 1985 were recorded photographically from an oscilloscope screen,
or on analog tape using a Nagra IV SJ tape recorder and later digitized. We measure the
duration of an EOD pulse as the time between the first and last points that deviate from
baseline by more than 2% of peak-to-peak amplitude.
Stomatorhinus ivindoensis new species
Figs. 1 & 2.
Holotype. CU 85157 (original specimen no. 2161), male, 43.5 mm SL. Gabon, “Bialé
Creek”: a small tributary of the Ivindo River inside the Ipassa Plateau Reserve near
Makokou, (0° 32.3’ N, 12° 49.6’ E). Dip net, C.D. Hopkins, 2 September 1975.
Paratypes. Seventy-two specimens from three localities. The 10 paratypes selected
for a complete set of measurements are indicated in Table 1.
Near village of Ébiègn on Rte. N.4, ca. 18 km E. of Makokou, Gabon (0° 35.5’ N, 12°
43.0’ E), 3 Oct 1979, R. Lewis: CU 85465 (32, without specimen nos.), 20.9–53.3 mm SL.
AMNH 235053 (10, without specimen nos.), 34.2–49.8 mm SL. MNHN 2004-1750–1759

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ZOOTAXA (10, without specimen nos.), 38.4–50.7 mm SL. MRAC 2004-32-P-1–10 (10, without
specimen nos.), 29.8–48.1 mm SL.
Balé Creek below bridge, ca. 500 m from the IRET field station on Ipassa Plateau, ca.
7 km SE of Makokou, Gabon (0° 31.1’ N, 12° 48.0’ E): CU 75437 (2, specimen nos. 1003,
1004), 37.9, 40.8 mm SL, 27 Oct 93, C.D. Hopkins. CU 86244 (2, specimen nos. 2143,
2144), 39.3, 41.1 mm SL, 16 Jan 98, C.D. Hopkins et al. CU 86247 (3, specimen nos.
2002, 2010, 2012), 42.3–49.5 mm SL, 11 Jan 98, C.D. Hopkins et al.
Creek at Makatabongoy crossing road from Makokou-Okondja (R.15), Gabon (0°
08.15’ N, 13° 43.0’ E): CU 86245 (3, specimen nos. 2223, 2352, 2358), 45.2–48.3 mm SL,
3 Oct 79, C.D. Hopkins et al.
FIGURE 1. Drawing of Stomatorhinus ivindoensis n. sp. holotype, 43.8 mm SL. Drawn by Vera
Ming Wong.
Additional (non-type) specimens.
Balé Creek, IRET field station on Ipassa Plateau, SE of Makokou, Gabon (0° 31’ N,
12° 48.0’ E): CU 85385 (3) 30.0–44.8 mm SL, 29 Nov 1976, C.D. Hopkins. CU 85486 (1,
specimen no. 2367) 43.0 mm SL, 28 Jul 1976, C.D. Hopkins. CU 85496 (1, specimen no.
85–230) 38.7 mm SL, 9 Dec 1985, J. Crawford. CU 83094 (1, specimen no. 4879) 39.8
mm SL, 26 Aug 2001, C.D. Hopkins & M.E. Arnegard. CU 75442 (1, specimen no. 1027)
36.8 mm SL, 29 Oct 1993, C.D. Hopkins & M.A. Friedman. CU 79703 (1, specimen no.
2074) 45.1 mm SL, 15 Jan 1998, C.D. Hopkins et al. CU 86243 (2, specimen nos. 2078,
2155) 33.6, 46.7 mm SL, 15 Jan 1998, C.D. Hopkins et al.
Nyamé Pendé Creek inside Ipassa Plateau Reserve (0° 30’ N, 12° 47’ E): CU 85152
(1, specimen no. 2101) 44.3 mm SL, 5 Aug 1975, C.D. Hopkins & R. Askins. CU 86246
(2, specimen nos. 2133, 2136) 38.0, 40.0 mm SL, 17 Jan 1998, C.D. Hopkins et al. CU
89030 (1) 43.0 mm SL, 20 Sep 2002, Hopkins et al.
Mindouba Creek on route to IRET station (0° 31.6’ N, 12° 48.2’ E): CU 89048 (1,
specimen no. 5701) 41.9 mm SL, 18 Sep 2002, C.D. Hopkins et al.

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Near mouth of Mié Creek into Ivindo River, across from Ipassa Reserve (0° 27.3’ N,
12° 48.5’E): CU 85123 (6), 21.3–49.6 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins.
CU 85128 (10), 35.5–48.0 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins. CU 85156
(1, specimen no. 2150), 47.4 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins.
Near villages of Ébiègn and Èdzua Megne on route N.4 ca. 16 km E. of Makokou
(approx. 0° 35.5’ N, 12° 43’E): CU 85131 (11), 29.5–55.7 mm SL, 9 Sep 1976, C.D. Hop-
kins. CU 85132 (17, specimen nos. between 3067 and 3093), 21.0–44.7 mm SL, 1 Oct
1979, R. Lewis. CU 85151 (12, specimen nos. between 3114 and 3125), 36.5–47.1 mm
SL, 1 Oct 1979, R. Lewis. CU 85153 (15, specimen nos. between 3095 and 3113), 27.1–
47.1 mm SL, 1 Oct 1979, R. Lewis. CU 85154 (19, specimen nos. between 3045 and
3066), 26.2–51.2 mm SL, 1 Oct 1979, R. Lewis. CU 85446 (71), 20.5–52.0 mm SL, 3 Oct
1979, R. Lewis. CU 85464 (16), 32.2–50.8 mm SL, 10 Oct 1979, R. Lewis. CU 85487 (1,
specimen no. 5015) 38.9 mm SL, Sep 2002, C.D. Hopkins. CU 85124 (4) 30.0–48.5 mm
SL, 7 Nov 1979, R. Lewis. CU 85126 (4) 24.6–44.5 mm SL, 24 Oct 1979, R. Lewis. CU
85503 (16) 32.6–51.0 mm SL, 7 Nov 1979, R. Lewis. CU 85378 (19) 32.6–52.7 mm SL, 1
Dec 1979, R. Lewis. AMNH 231101 (21) 23.6–51.7mm SL, 6 Nov 1975, W. Harder.
AMNH 231102 (51) 22.1–49.8 mm SL, 18 Nov 1975, W. Harder. AMNH 231173 (17)
23.2–51.33 mm SL, 3 Aug 1975, W. Harder.
Near village of Mbès on route N.4 ca. 18 km E. of Makokou (0° 34.8’ N, 12° 41’E):
CU 85125 (6), 37.0–45.7 mm SL, 12 Aug 1976, C.D. Hopkins. CU 85155 (1, specimen
no. 2365), 52.0 mm SL, 12 Aug 1976, C.D. Hopkins. AMNH 231100 (30) 32.7–55.1 mm
SL. 20 Sept. 1975, W. Harder. AMNH 231104 (1) 45.9 mm SL, 20 Nov 1975, W. Harder.
AMNH 231105 (2) 44.5, 48.8 mm SL, 20 Nov 1975, W. Harder. AMNH 231106 (2) 41.3,
46.4 mm SL, 20 Nov 1975, W. Harder.
8 km downstream of IRET Ipassa Plateau Reserve station (0° 27.3’ N, 12° 48.8’ E):
CU 85160 (9), 28.0–40.1 mm SL, 3 Aug 1976, C.D. Hopkins.
23 km W of Makokou along “route Fang” (N.4) (0° 33.5’ N, 12° 37.7’ E): CU 85159
(2) 40.3, 43.5 mm SL, 1 Dec 1979, R. Lewis.
7 km W of Makokou along “route Fang” (N.4) (0° 34.3’ N, 12° 46.5’ E): CU 85158 (1,
specimen no. 2366) 44.0 mm SL, 1 Dec 1976, C.D. Hopkins.
Along banks of Ivindo River near Makokou (0° 33’ N, 12° 51’E): CU 85127 (13) 27.2-
46.3 mm SL, 1 Aug 1975, C.D. Hopkins & R. Askins. CU 85477 (3) 27.9–45.5 mm SL, 1
Dec 1976, C.D. Hopkins.
Weni Creek, Makokou (30° N, 12°50’E): CU 85130 (8) 28.0–41.8 mm SL. 22 Sep
1976, C.D. Hopkins. CU 85129 (16) 26.7–47.6 mm SL. 1 Oct 1976. C.D. Hopkins. CU
85499 (1) 30.6 mm SL, 11 Oct 1976, C. D. Hopkins.
Creek crossing road from Makokou to Okondja (R.15), ca. 60 km SE of Makokou (0°
18’ N, 13° 13’E): CU 85420 (1, specimen no. 5014), 40.2 mm SL, C.D. Hopkins & R.
Lewis.
Near Makokou, Gabon; precise locality not specified: AMNH 231103 (1) 42.8 mm

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ZOOTAXA SL, 20 Nov 1975, W. Harder. AMNH 231151 (2) 30.0, 49.2 mm SL, 1978, W. Harder.
AMNH 231166 (1) 25.5 mm SL, 29 July 1975, W. Harder. AMNH 231215 (1) 50.4 mm
SL, no date, W. Harder.
FIGURE 2. Photograph (A) and radiograph (B) of preserved holotype of Stomatorhinus ivindoen-
sis n. sp., CU 85157, 43.8 mm SL, male; (C) live paratype specimen no.1004, CU 75437, 40.8 mm
SL, male; (D) preserved paratype, CU 85465, 52.2 mm SL, female.

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TABLE 1. Descriptive morphometrics and meristics for Stomatorhinus ivindoensis n.sp. Paratypes
included in measurements are: CU 85465 (2 of 32, no specimen nos.), 52.2, 53.3 mm SL, CU 75437
(2 of 2, specimen nos. 1003, 1004), 37.9 & 40.8 mm SL, CU 86244 (2 of 2, specimen nos. 2143,
2144), 39.3, 41.1 mm SL, CU 86247 (1 of 3, specimen no. 2012), 42.3 mm SL, CU 86245 (3 of 3,
specimen nos. 2223, 2352, 2358), 45.2–48.3 mm SL.
Character Holotype N min max mean Std. Dev.
Standard length, mm 43.75 11 37.37 53.09 44.37 4.75
Head length, mm 14.26 11 12.50 16.01 14.26 1.01
Percent of standard length
Maximum body depth 27.04 11 23.92 26.67 25.87 1.49
Head length 32.41 11 30.16 33.87 32.26 1.28
Snout length 7.77 11 7.77 8.40 8.10 0.19
Pre-dorsal distance 65.62 11 65.62 70.60 67.92 1.56
Pre-anal distance 59.98 11 59.98 67.73 63.27 2.24
Pre-pelvic distance 45.97 11 45.36 49.75 47.31 1.19
Pre-pectoral distance 30.83 11 30.57 33.36 31.68 0.87
Caudal peduncle depth 6.33 11 5.31 6.49 6.03 0.46
Caudal peduncle length 14.24 11 14.17 16.46 14.92 0.82
Head width 14.67 11 13.96 16.43 15.13 0.76
Pectoral fin length 18.81 11 15.96 19.81 18.42 0.99
Pelvic fin length 10.03 11 9.57 10.79 10.28 0.44
Pelvic-anal fin distance 15.22 11 15.22 21.66 17.79 2.31
Anal fin base length 25.44 11 22.83 25.44 24.05 0.85
Dorsal fin base length 21.10 11 18.15 21.10 19.89 0.86
Percent of head length
Snout length 23.98 11 23.68 27.57 25.15 1.22
Post-orbital length 69.25 11 66.91 71.83 69.41 1.52
Head width 45.28 11 42.52 50.59 46.96 2.47
Head depth 68.34 11 58.35 68.92 64.47 3.39
Eye diameter 9.87 11 6.65 10.10 8.30 1.19
Inter-nostril distance 24.82 11 23.04 26.70 24.96 1.11
Ratios
Inter-orbital width as % head width 84.42 11 71.92 90.41 76.72 5.77
Pre-anal distance/pre-dorsal distance 0.91 11 0.89 1.03 0.93 0.04
Caudal peduncle depth as % CP length 44.46 11 37.29 45.33 40.55 3.42
Length of dorsal/length of anal 0.83 11 0.80 0.88 0.83 0.02
Counts median quartile
range
Dorsal rays 17 11 14 17 16 1.50
Anal rays 21 11 19 21 20 1.00
Anal rays before dorsal 5 11 5 5 5 0
Pectoral rays 8 11 8 9 9 1.00
Pelvic rays 6 11 6 6 6 0
Caudal peduncular scales 12 11 12 12 12 0
Teeth, upper jaw 7 11 7 8 7 1.00
Teeth, lower jaw 8 11 8 9 8 1.00
Total vertebrae 36 11 36 36 36 1.00
Scale rows from pelvic fin origin to lateral line 13 11 11 13 11 1.00
Lateral line scales with tube & exposed pore 24 11 22 34 26 2.50
Scales along longitudinal line 46 11 44 50 46 3.50

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ZOOTAXA Diagnosis: Stomatorhinus ivindoensis is recognized by the combination of the follow-
ing characteristics: (1) very small adult size (specimens larger than 56 mm SL never
observed) with most adults between 35 and 48 mm SL; (2) caudal peduncle of moderate
width (caudal peduncle depth 37–45% of caudal penduncle length); (3) a small eye, 6.7–
10% of HL; (4) 8 to 9 pectoral rays and 14 to 17 dorsal fin rays; (5) first 22 to 28 scales
along lateral line bearing pores, last pore-bearing scale lying posterior to a vertical through
origin of anal fin, but positioned well in advance of caudal peduncle; (6) lobes of the cau-
dal fin broad and rounded, without distinct points at apices.
Description: A very small Stomatorhinus not known to surpass 56 mm SL. Morpho-
metric ratios and meristics presented in Table 1. Body depth and width as proportions of
SL are in middle range for species of this genus. In all but gravid females, depth at origin
of anal fin equal to or slightly less than depth at mid-body. Greatest width at opercles. Dor-
sal and ventral profiles gently convex. The head profile is slightly convex above the eye,
the snout is rounded to somewhat truncate and projects slightly beyond the mouth. Mouth
small. No submental swelling. Eye small, covered by epidermis. Inter-orbital distance is
72–90% of head width. Nostrils well separated with posterior nostril located near rictus of
mouth. Teeth 7–8/8–9, usually 7/8, bicuspid. Head (including eye), upper back and belly
covered by epidermis that is translucent in life, semi-opaque in preservation. When
pressed to side, tip of pectoral fin extends well past origin of pelvic fin. Pectoral fin has 8
or 9 rays. Dorsal and anal fins roughly symmetrical above and below body axis, the anal
fin (of 19–21 rays) slightly longer, with the dorsal fin (of 14–17 rays) originating at verti-
cal through the origin of the fourth or fifth anal fin ray; the origins of the last dorsal and
last anal fin rays at roughly the same vertical. Lobes of caudal fin short, very rounded and
blunt. Caudal peduncle relatively short (14–16.5% of SL), of moderate depth (37–45% of
length), with 12 circumpeduncular scales. First 22–28 scales along lateral line bearing
pores, last pore-bearing scale lying past vertical through origin of anal fin. Total scales
along longitudinal line 44–50. Scale rows between origin of pelvic fin and lateral line scale
11 to 13. Total vertebrae 36 (excluding urostyle).
Color: In life, specimens are uniformly dark chocolate brown, with little patterning in
pigment along the body. Fins are translucent with dark brown pigmented rays. In alcohol,
thick epidermis overlying head (including eye), upper back and belly appears opaque.
Size and sexual maturity: Review of 504 specimens in 54 lots from several localities
reveals no specimens larger than 56 mm SL. Mature males are identifiable by a pro-
nounced anal fin notch from about 35 mm SL. Gravid females are often enormously dis-
tended with eggs (e.g. female paratype shown in Fig 2D).
Distribution and ecology: All known collections of S. ivindoensis come from the
upper Ivindo River (Fig. 3). Most were made in the vicinity of Makokou and the nearby
field station located inside the Ipassa Plateau Reserve on the right bank of the Ivindo
River. The species is usually taken along the margin of small forest streams (Fig. 4) in root
tangle where it occurs with other species of mormyrids, but has also been taken along the

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margin of the Ivindo River proper in deep water. Individuals are often found spaced apart
at intervals of 50 cm to one meter. Diet of this species has not been studied, but is probably
similar to that reported for S. polli Matthes 1964 in which stomach contents were domi-
nated by small crustaceans and insect larvae.
FIGURE 3. Collection sites of Stomatorhinus ivindoensis n. sp. (circles) and S. walkeri (triangles)
in the Ivindo and Ogooué River basins of Gabon and the Kouilou-Niari basin of the Republic of
Congo. Shaded areas delimit the boundary of the Lower Guinea ichthyofaunal province of West
Central Africa.

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FIGURE 4. Typical forest creek habitat of Stomatorhinus ivindoensis n. sp.: upper “Balé Creek”
within the Ipassa Plateau Reserve near Makokou, Gabon.
Electric organ discharge: Stomatorhinus ivindoensis has a 110 to 720 microsecond
duration EOD waveform with three to four peaks in the discharge (Fig. 5A–F). The EOD
begins with a small head-negative phase or peak, P0, followed by a larger head-positive
phase, P1, followed by the largest head-negative peak, P2. In some fish, the discharge ends
with a final head-positive phase, P3. The peak spectral frequency of the Fourier Transform
of the EOD is between 4000 Hz and 16,000 Hz. Average peak heights, total durations, and
spectral peak frequencies for this species, are listed in Table 2. The EOD is sexually
dimorphic among sexually mature individuals. Juvenile male EODs are similar to female
EODs. Male EODs are longer in duration and have lower FFT peaks than females. They
also differ in the heights of peaks P0 and P1 relative to the full peak to peak height com-
pared to females (Table 2). The EOD of a juvenile of this species was reported by Heymer
& Harder (1975).
Etymology: Named for the Ivindo River of Gabon.

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FIGURE 5. EOD waveforms (left) and power spectra (right) for Stomatorhinus ivindoensis n. sp.
The holotype of S. ivindoensis, a male, is shown in A and B. Peaks are numbered in order from P0
to P3. EOD waveforms are centered about the largest head-negative peak and plotted with head
positivity upward. Power spectra are normalized so that the peak energy is adjusted to 0 dB. EODs
of reproductive males (E, F) are longer in duration and have a lower peak power frequency than
those of females (C, D). Individual specimen numbers are indicated beneath waveforms; F=female,
M=male, H=holotype. Time base = 0.1 millisecond.

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ZOOTAXA TABLE 2. Descriptive statistics on measures of EOD waveforms from Stomatorhinus ivindoensis
ranging in size from 34 to 49.5 mm and Stomatorhinus walkeri ranging in size from 33 to 99 mm
SL. Peak heights have been normalized to the peak to peak height. Negative numbers indicate
head-negative peaks. Only sexually mature males and females are included in the table. EOD dura-
tions are measured from the first and last points that deviated from the baseline by more than 2% of
peak-to-peak amplitude.
1 Male S. ivindoensis differ from all three other groups using Scheffe’s post-hoc test, p < 0.01.
2 Male S. ivindoensis differ from female S. ivindoensis. Scheffe’s post-hoc test, p < 0.05
Discussion
External proportions and counts of S. ivindoensis n. sp. (Table 1 and above section) distin-
guish this species from other congeners. Here we highlight the most prominent of these
differences.
As pointed out by Poll (1945), S. puncticulatus Boulenger 1899 and S. patrizii can be
separated from other Stomatorhinus, including S. ivindoensis, by their deep bodies (depth
more than 33% SL) and long, narrow caudal penduncles (caudal peduncle depth 25%–
31% of caudal peduncle length). In all other species of Stomatorhinus body depth is 33%
of SL or less and caudal peduncle depth is 32% of caudal peduncle length or more. In S.
ivindoensis, body depth ranges from 24–27% of SL and caudal peduncle depth ranges
from 37–45% of caudal peduncle length.
Eye diameter distinguishes two Stomatorhinus species from all others: S. schoutedeni
Poll 1945 has a larger eye than other Stomatorhinus (~20% of HL, ~66% of interorbital
distance), while S. microps Boulenger 1898, as its name implies, has a smaller eye than all
other species (~6% of HL, ~17% of interorbital distance) that is partially obscured by
overlying skin. In S. ivindoensis the eye diameter is 6.7–10% of HL and 35–44% of inter-
orbital distance.
Members of the type series of three Stomatorhinus species—S. polylepis Boulenger
1899, S. corneti Boulenger 1899, and S. ater Pellegrin 1924—are far larger than the 56
nmean
P0
height
S.D. mean
P1
height
S.D. mean
P2
height
S.D. mean
P3
height
S.D. mean
FFT
peak
S.D. mean
EOD
duration
S.D.
% % % % (Hz) (µs)
S. ivindoensis
Female 17 -4.913.8 23.927.1 -67.6 4.3 13.128.7 1301712562 185162
Male 12 -12.017.0 31.827.0 -66.7 4.9 28.528.5 759313661 3741172
S. walkeri
Female 8 -2.512.2 26.3 6.4 -69.2 6.7 19.5 10.3 1826816069 138163
Male 6 -0.611.0 24.7 5.0 -73.8 6.0 24.4 10.5 1669917455 140184

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mm maximum observed adult SL of S. ivindoensis and additionally differ from the new
species in counts and measures. For S. polylepis, one of the syntypes exceeds 100 mm SL
and two others are above 80 mm SL. Further distinguishing this species from S. ivindoen-
sis are its high scales counts: S. polylepis has 53 or more scales in longitudinal series and
18–22 around the caudal peduncle vs. 44–50 longitudinal scales and 12 circumpeduncular
scales in S. ivindoensis. Lateral line scales bearing tubes extend onto the caudal peduncle
in S. polylepis while they do not in S. ivindoensis. The holotype of S. corneti has a SL of
93.3 mm and a distinctive rectilinear, gently sloping head profile above the eye that makes
an abrubt, nearly vertical downward turn above the anterior nostril; the snout is truncate
and does not extend beyond the mouth and the tooth count is 9/10. In S. ivindoensis, the
head profile is slightly convex above the eye, the snout is rounded and projects slightly
beyond the mouth and the tooth count is modally 7/8. The S. ater type series ranges in size
from 70–94 mm SL and the four examined syntypes (of six total) examined exhibit deeper
heads (head depth 74.4–79% of HL) than do specimens of S. ivindoensis (head depth 59–
69% of HL). Additionally, the eye in S. ater is significantly larger than that of S. ivindoen-
sis (12–15% of HL, vs. 6.7–10% in S. ivindoensis) and S. ater has 10 pectoral rays com-
pared to the 8–9 in S. ivindoensis.
Two described species of Stomatorhinus—S. humilior Boulenger 1899 and S. kunun-
guensis Poll 1945—are considerably more elongate than S. ivindoensis. In S. humilior the
body depth above the anal fin origin is 19–21.5% of SL, in S. kununguensis it is 21–22%,
while in S. ivindoensis it is 23–27 %. Members of the type series of both species exceed 70
mm SL, a significantly larger size than any known S. ivindoensis. Furthermore, S. kunun-
guensis has larger eye than S. ivindoensis (10.5–13% of HL vs. 6.7–10% of HL).
In Tables 2–5 and in Figures 6–9, S. ivindoensis is compared with the two species it
resembles most closely, S. fuliginosus and S. polli, as well as with S. walkeri, the sole Sto-
matorhinus species previously described from the Ogooué River basin.
S. fuliginosus, from the Itimbiri River in the Congo basin (Fig. 6 C, D), is the only
described Stomatorhinus for which the entire type series is within the observed size range
of S. ivindoensis and many of its proportions and counts are similar to those observed for
S. ivindoensis. Harder (2000) assigned the Stomatorhinus specimens from the Ivindo basin
to this species. However, S. fuliginosus differs from S. ivindoensis by having a deeper cau-
dal peduncle (caudal peduncle depth is 50–69% of caudal peduncle length vs. 37–45% in
S. ivindoensis), a wider head (head width is 50–56% of head length vs. 43–50% in S. ivin-
doensis), and a smaller inter-orbital width (57–69% of head width vs. 72–90% in S. ivin-
doensis). Differences between these two species in two morphometric ratios are illustrated
in Fig. 7A. Furthermore, S. fuliginosus has fewer lateral line scales with exposed tubes and
pores relative to S. ivindoensis (12–21 in S. fuliginosus vs. 22–34 in S. ivindoensis). In all
eight syntypes of S. fuliginosus, the lateral line series of tubes and pores terminates mid-
way along the side, well in advance of a vertical through the origin of the anal fin. In S.
ivindoensis, the lateral line series of tubes and pores continues at least a short distance

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ZOOTAXA beyond a vertical through the origin of the anal fin, but always terminates well in advance
of the caudal peduncle. The caudal fins of all eight S. fuliginosus syntypes are damaged to
one degree or another. Poll (1941) describes the lobes of the caudal fin of S. fuliginosus as
“obtuse,” however, examination of the S. fuliginosus syntypes and the illustration of the
holotype indicates that the lobes of the caudal fin are narrower than those observed in S.
ivindoensis specimens. No EOD information is available for S. fuliginosus. Taken
together, we view the differences between the Ivindo basin Stomatorhinus specimens and
the type series of S. fuliginosus as sufficient to recognize the two as distinct species.
FIGURE 6. Species of Stomatorhinus to which Stomatorhinus ivindoensis n. sp. is closely com-
pared in study: (A) S. walkeri syntype BMNH 1867.5.3.16, 85.6 mm SL; (B) S. walkeri live speci-
men no. 2880, CU 80237, 95 mm SL; (C) S. fuliginosus syntype MRAC 6652, 37.7 mm SL; (D) S.
fuliginosus syntype MRAC 6648, 33.5 mm SL; (E) S. polli paratype MRAC 138993, 61.3 mm SL;
(F) S. polli paratype MRAC 138977, 58.7 mm SL.
It remains unclear whether S. fuliginosus is actually as small a species as S. ivindoen-
sis. Four of the eight S. fuliginosus syntypes are within the size range of sexually mature
individuals of S. ivindoensis, yet none show the characteristic anal fin notch of males, nor
abdominal distension from eggs (gonads were not examined). It is thus possible that all the
syntypes of S. fuliginosus are juveniles and considerably smaller than adult size. (No non-
type specimens from near the type locality are available for to ascertain the size range of
adults.) If, as it seems likely, adults of S. fuliginosus achieve larger sizes than adults of S.
ivindoensis, S. ivindoensis is the smallest known mormyrid species.

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TABLE 3. Descriptive morphometrics and meristics for the 8 syntypes of Stomatorhinus fuligino-
sus. Asterix indicates non-overlapping range with S. ivindoensis n. sp.
Character N min max mean Std. Dev.
Standard length, mm 8 29.62 39.28 34.32 3.09
Head length, mm 8 10.33 12.51 11.14 0.71
Percent of standard length
Maximum body depth 8 22.91 26.61 25.11 1.23
Head length 8 30.85 34.88 32.53 1.22
Snout length 8 6.57 8.95 7.44 0.84
Pre-dorsal distance 8 66.99 68.91 68.27 0.7
Pre-anal distance 8 61.1 64.13 62.66 1.14
Pre-pelvic distance 8 44.13 47.98 46.32 1.41
Pre-pectoral distance 8 31.26 34.84 32.75 1.26
Caudal peduncle depth 8 7.31 8.38 7.71 0.41 *
Caudal peduncle length 8 11.14 14.74 13.29 1.31
Head width 8 15.78 18.37 16.98 0.96
Pectoral fin length 8 18.25 20.76 19.37 0.92
Pelvic fin length 8 9.67 11.1 10.31 0.48
Pelvic-anal fin distance 8 15.65 17.18 16.37 0.55
Anal fin base length 8 23.65 26.27 25.35 0.94
Dorsal fin base length 8 20.08 22.73 21.45 1.04
Percent of head length
Snout length 8 20.62 25.65 22.83 1.78
Post-orbital length 8 68.98 76.48 72.76 2.84
Head width 8 49.56 55.72 52.2 2.27 *
Head depth 8 64.67 73.66 67.37 3.19
Eye diameter 8 5.95 9.99 8.23 1.63
Inter-nostril distance 8 20.05 28.97 23.45 3.04
Ratios
Inter-orbital width as % head width 8 57.3 68.54 61.25 4.32 *
Pre-anal distance/pre-dorsal distance 8 0.89 0.94 0.92 0.02
Caudal peduncle depth as % CP length 8 50.09 69.09 58.4 6.39 *
Length of dorsal/length of anal 8 0.79 0.88 0.85 0.03
Counts median quartile range
Dorsal rays 6 17 18 17 1.00
Anal rays 7 21 23 22 1.00
Anal rays before dorsal 8 4 5 5 0
Pectoral rays 8 8 9 9 0
Pelvic rays 8 6 6 6 0
Caudal peduncular scales 8 12 14 12 0
Teeth, upper jaw 8 7 8 7 0
Teeth, lower jaw 8 8 10 8 0.25
Total vertebrae 8 36 36 36 0
Scale rows from pelvic fin origin to lateral line 3 12 13 12 0.50
Lateral line scales with tube & exposed pore 8 12 21 18 5.00 *
Scales along longitudinal line 8 44 47 45 2.25

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ZOOTAXA TABLE 4. Descriptive morphometrics and meristics for seven paratypes and one non-type of Sto-
matorhinus polli. Asterix indicates non-overlapping range with S. ivindoensis n. sp.
Character N min max mean Std. Dev.
Standard length, mm 8 44.10 61.27 53.90 6.46
Head length, mm 8 13.54 18.43 16.28 1.87
Percent of standard length 8
Maximum body depth 8 23.90 26.49 25.47 0.81
Head length 8 29.07 31.85 30.23 0.89
Snout length 8 6.97 7.59 7.30 0.21 *
Pre-dorsal distance 8 64.29 67.88 66.36 1.08
Pre-anal distance 7 58.38 62.24 59.94 1.33
Pre-pelvic distance 8 41.75 48.13 43.66 2.21
Pre-pectoral distance 8 27.87 31.22 29.27 1.03
Caudal peduncle depth 8 5.63 6.65 6.31 0.32
Caudal peduncle length 7 15.01 16.72 15.72 0.85
Head width 8 14.90 16.52 15.70 0.49
Pectoral fin length 6 17.40 19.95 18.70 1.10
Pelvic fin length 7 9.87 11.50 10.91 0.64
Pelvic-anal fin distance 7 16.12 20.08 17.44 1.36
Anal fin base length 7 23.02 26.51 25.34 1.12
Dorsal fin base length 7 20.05 23.20 21.53 1.08
Percent of head length
Snout length 8 23.46 25.01 24.17 0.59
Post-orbital length 8 68.98 73.24 71.09 1.59
Head width 8 46.80 55.14 51.98 2.65
Head depth 8 58.42 74.42 67.67 5.22
Eye diameter 8 11.12 13.43 12.00 0.72 *
Inter-nostril distance 8 21.10 23.96 22.37 1.13
Ratios
Inter-orbital width as % head width 8 53.34 61.49 58.93 2.57 *
Pre-anal distance/pre-dorsal distance 8 0.87 0.94 0.90 0.02
Caudal peduncle depth as % CP length 8 36.81 44.26 40.25 2.67
Length of dorsal/length of anal 7 0.79 0.91 0.85 0.04
Counts median quartile range
Dorsal rays 4 17 18 18 0.25
Anal rays 4 21 22 21 0.25
Anal rays before dorsal 4 5 5 5 0
Pectoral rays 8 8 9 9 0
Pelvic rays 8 6 6 6 0
Caudal peduncular scales 5 12 12 12 0
Teeth, upper jaw 4 7 7 7 0
Tee th, lower jaw 8 8 8 8 0
Total vertebrae 3 36 36 36 0
Scale rows from pelvic fin origin to lateral line 8 12 12 12 0
Lateral line scales with tube & exposed pore 6 22 29 26 0.75
Scales along longitudinal line 6 43 48 46 3.00

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TABLE 5. Descriptive morphometrics and meristics for Stomatorhinus walkeri; includes the two
syntypes and twelve non-type specimens from the Ogooué River, Gabon. Asterix indicates non-
overlapping range with S. ivindoensis n. sp.
Character Syntype 1 Syntype 2 N min max mean Std. Dev.
Standard length, mm 85.59 86.34 14 51.50 91.52 75.66 12.46
Head length, mm 24.23 24.84 14 16.90 26.65 22.59 3.06
Percent of standard length 14
Maximum body depth 27.97 27.00 14 25.14 29.04 27.48 1.18
Head length 28.31 28.77 14 28.31 33.04 30.02 1.29
Snout length 8.05 7.42 14 7.42 9.11 8.09 0.49
Pre-dorsal distance 67.79 67.28 14 62.38 68.01 65.81 1.83
Pre-anal distance 58.00 61.41 14 58.00 62.00 59.94 1.30
Pre-pelvic distance 40.83 40.61 14 40.61 45.67 42.19 1.44
Pre-pectoral distance 28.15 27.59 14 26.80 30.56 28.53 1.07 *
Caudal peduncle depth 6.30 5.51 14 5.23 6.65 5.84 0.40
Caudal peduncle length 16.19 14.78 14 14.78 16.70 15.97 0.66
Head width 13.72 14.06 14 13.27 15.14 14.34 0.51
Pectoral fin length 17.83 17.69 14 17.69 22.71 19.84 1.57
Pelvic fin length 11.05 10.76 14 9.95 12.21 11.12 0.62
Pelvic-anal fin distance 17.83 20.80 14 16.15 20.80 18.33 1.18
Anal fin base length 26.43 25.69 14 24.08 26.66 25.50 0.86
Dorsal fin base length 23.40 22.78 14 20.64 23.57 22.08 0.88
Percent of head length
Snout length 28.44 25.81 14 25.21 28.71 26.95 1.00
Post-orbital length 63.27 65.14 14 54.50 68.71 64.65 4.58
Head width 48.45 48.87 14 43.79 49.52 47.81 1.59
Head depth 79.28 76.57 14 63.76 79.28 69.85 5.20
Eye diameter 12.59 12.48 14 8.99 13.69 11.81 1.07
Inter-nostril distance 22.16 21.14 14 21.14 28.42 24.90 2.19
Ratios
Inter-orbital width as % head width 65.84 63.67 14 62.93 83.24 73.74 7.27
Pre-anal distance/pre-dorsal distance 0.86 0.91 14 0.86 0.95 0.91 0.02
Caudal peduncle depth as % CP length 38.89 37.30 14 32.21 42.20 36.63 2.98
Length of dorsal/length of anal 0.89 0.89 14 0.83 0.90 0.87 0.02
Counts median quartile
range
Dorsal rays 20 19 14 17 20 19 1.00
Anal rays 22 22 14 21 22 22 0
Anal rays before dorsal 5 5 14 4 5 5 0
Pectoral rays 10 10 14 10 10 10 0 *
Pelvic rays 6 6 14 6 6 6 0
Caudal peduncular scales 14 12 14 12 14 12 0
Teeth, upper jaw 9 9 14 7 9 9 3.00
Teeth, lower jaw 10 10 14 8 10 8 1.75
Total vertebrae 37 37 7 38 39 38 1.00 *
Scale rows from pelvic fin origin to lateral line 14 14 14 12 14 13 1.00
Lateral line scales with tube & exposed pore 42 43 9 39 48 42 3.00 *
Scales along longitudinal line 52 49 14 46 53 50 4.50

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ZOOTAXA S. polli from the Tshuapa River in the Middle Congo basin (Fig. 6E, F) is somewhat
larger than S. ivindoensis: the largest in the type series measures 63.5 mm SL and six of the
eight others exceed the greatest size observed for S. ivindoensis. The depth to width ratio
of this species is approximately the same as that for S. ivindoensis, as are scale counts and
the number of scales bearing lateral line tubes and pores. As in S. ivindoensis, the lobes of
the caudal fin are broad and rounded, lacking distinct points at the apices. However, this
species differs from S. ivindoensis in having a shorter snout relative to body length (7–
7.6% of SL vs. 7.8–8.4% in S. ivindoensis), a larger eye (11–13.4% of HL vs. 6.7–10% in
S. ivindoensis) and a smaller inter-orbital width as a proportion of head width (53–61.5%
vs. 72–90.4% in S. ivindoensis). Additionally, S. polli has a narrower head (head width 59–
64% of HL to end of opercle) than S. ivindoensis (head width 66–78% of HL to end of
opercle). Differences between these two species in two morphometric ratios are illustrated
in Fig. 7B.
FIGURE 7. Selected morphometric ratios of S. ivindoensis n. sp. compared to those in S. fuligino-
sus (A) and S. polli (B). IO= interorbital distance, HW= head width, CPD=caudal peduncle depth
measured at terminus of anal fin, CPL=caudal peduncle length, E=eye diameter, HL=head length.
Stomatorhinus walkeri (Fig 6A, B) is the type species of the genus and is, apart from
the species described here, the only other Stomatorhinus species described from and
known to occur within the Ogooué River basin. It is a considerably larger species than S.
ivindoensis, with individuals exceeding a length of 90 mm SL. While the ranges of many
morphometric ratios overlap those for S. ivindoensis, the pre-pectoral distance is a smaller
proportion of SL (26.8–30.6%) than in S. ivindoensis (30.6–33.4%). The lobes of the cau-
dal fin are more narrow and pointed at the apices than those of S. ivindoensis. Counts eas-
ily separate the two species. Stomatorhinus walkeri have 10 pectoral rays; S. ivindoensis
have no more than 9. Stomatorhinus walkeri have 37 to 39 total vertebrae; S. ivindoensis

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have 36. S. walkeri have lateral line scales with exposed tubes and pores that extend onto
the base of the caudal peduncle. In S. ivindoensis lateral line scales with exposed tubes and
pores terminate well in advance of the caudal penduncle. Furthermore, the body coloration
in life of S. walkeri is light to medium gray with a purplish cast in daylight (see Fig. 6B)
whereas S. ivindoensis are always a dark chocolate brown.
In a principal components analysis of the correlation matrix of 24 log-transformed
measures, the type specimens of S. ivindoensis form a coherent cluster on a plot of the sec-
ond and third factors that is non-overlapping with the type specimens of S. fuliginosus, S.
polli, S. walkeri, S. corneti and S. ater (Fig. 8). We conclude that the significant morpho-
logical differences between Stomatorhinus specimens from the Ivindo River basin of
Gabon and all other described species in this genus warrant its recognition as a new spe-
cies.
FIGURE 8. Scores from types of S. ivindoensis n. sp. and five other Stomatorhinus species on the
second and third factors of a principal components analysis of the covariance matrix calculated
from 24 log-transformed morphometric measures. Twelve non-type specimens of S. walkeri and
one non-type of S. polli included. Variables loading most heavily on the second principal compo-
nent are caudal peduncle depth, interorbital distance and internostril distance. Variables loading
most heavily on the third principal component are eye diameter, post-orbital head length and caudal
peduncle length.
The addition of this Ivindo River-endemic Stomatorhinus further highlights the dis-
tinctiveness of this river’s fish fauna, already notable for species of mormyrids (Sullivan et
al. 2002), gonorhynchiforms (Géry 1964), cyprinodontiforms (Wildekamp 1993), and

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ZOOTAXA cichlids (Thys van den Audenaerde 1966) either endemic or shared only with the Ntem
River basin to the north.
Comparison of electric signals. The EOD of S. ivindoensis is similar to that of S.
walkeri from the Ogooué River basin of Gabon. The latter species has a shorter duration
EOD that measures 70 to 270 microseconds with an average spectral frequency peak at
17,355 Hz (Fig. 9A–D). We found no differences between the sexes or different age-
classes of S. walkeri comparing EODs from eight sexually mature females with six sexu-
ally mature males and with seven juveniles of 34–99 mm SL, although all samples were
taken during the dry season when most mormyrids are not breeding. The EOD of S. walk-
eri is characterized by two head-positive peaks of about the same amplitude (23% of peak
to peak height), separating a single large head negative peak. A weak head-negative phase
preceding P1 occurs in some individuals. Table 2 summarizes descriptive statistics on
EODs from 14 adult individuals. Although similar, EODs of Stomatorhinus walkeri differ
from those of S. ivindoensis by having a shorter waveform duration, higher peak spectral
frequency, and in the heights of peak P0 (Scheffe’s post-hoc comparison).
FIGURE 9. Waveforms and power spectra of EODs from Stomatorhinus walkeri (A–D), S. ater (E,
F) and S. patrizii (G, H) on the same time scale as those shown in Fig. 5. EOD waveforms are cen-
tered about the largest head-negative peak, normalized to the same peak-to-peak height and plotted
with head positivity upward for each trace. Power spectra are normalized so that the peak energy is
adjusted to 0 dB. Individual specimen numbers are indicated beneath waveforms; F=female,
M=male.
EOD recordings have been made for only two other species of Stomatorhinus that we
can confidently assign to described species. These are S. ater and S. patrizii. These speci-
mens were collected in Odzala Park in the Republic of Congo in 2002 by Drs. John Sulli-
van, John Friel, and Sébastien Lavoué. Five individuals of S. ater, ranging in size from

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57.8 to 83.5 mm SL were recorded (Fig. 9 E, F). The mean EOD duration is 69.3 micro-
seconds ± 10.0 (std. dev.) and the power spectrum peak occurred at 26,562 Hz ± 3,945.
The EOD waveform has four peaks, beginning with a small, head-negative peak of low
amplitude (4.5% of the peak to peak height). Thirteen individuals of S. patrizii, ranging in
size from 35 to 62 mm SL, were recorded (Fig. 9 G, H). The mean EOD duration is 88.4
microseconds ± 17.2 (std. dev.) and the power spectrum peak is 36,425 Hz ± 8,706. The
EOD waveform is complex, with as many as six peaks in many of the recordings.
Note. Specimens of S. ivindoensis have been identified as S. corneti in the following
previously published studies: Bass (1986); Heymer & Harder (1975); Hopkins (1980,
1981, 1986).
Comparative Material Examined. (All in alcohol.) Stomatorhinus ater Pellegrin
1924. 4 (of 6) syntypes: MRAC 15.097–15.099, MNHN 23–155; non-types: CU 87781
(1), CU 87893 (1), CU 87897 (1), CU 87912 (1), CU 87981 (1), CU 89099 (1), CU 89100
(3), CU 89190 (2). Stomatorhinus corneti Boulenger 1899, 1 (holotype): MRAC 638. Sto-
matorhinus fuliginosus Poll 1941. 8 syntypes: MRAC 66.546–553. Stomatorhinus
humilior Boulenger 1899, 2 (of 3) syntypes: MRAC 636, 637. Stomatorhinus kununguen-
sis Poll 1945, 1 lectotype: MRAC 21.573; 5 (of 8) paralectotypes: MRAC 21.574, 38.627,
48.785, 57.221–57.222. Stomatorhinus microps Boulenger 1898, 2 (of 7) syntypes: MRAC
68, MRAC 94. Stomatorhinus patrizii Vinciguerra 1928; non-types: CU 81662 (1), CU
87989 (1). Stomatorhinus polli Matthes 1964, 12 (of 43) paratypes: MRAC 69597, MRAC
120179–185, MRAC 138976–978, MRAC 138993. Stomatorhinus polylepis Boulenger
1899, 4 (of 9) syntypes: MRAC 640–643. Stomatorhinus puncticulatus Boulenger 1899, 2
(of 3) syntypes: MRAC 634, 635; non-types: CU 41319 (1). Stomatorhinus walkeri
(Günther 1867), syntypes 2 (of 2): BMNH 1867.5.3.15–16; non-types: CU 79708 (1), CU
80149 (4), CU 80227 (12), CU 80237 (3), CU 80245 (1), CU 80248 (1), CU 80255 (1),
CU 80256 (2), CU 80264 (2), CU 80304 (2), CU 80315 (2), CU 80347 (1), CU 80467 (1),
CU 80469 (1), CU 80472 (2), CU 80477 (2), CU 80523 (4), CU 80536 (1), CU 81069 (4),
CU 81076 (1), CU 81340 (6), CU 81341 (2), CU 81631 (9), CU 81638 (11), CU 82204 (1),
CU 83071 (1), CU 83261 (3). Petrocephalus affinis Sauvage 1879 (synonym of S. walk-
eri), holotype: MNHN A.894.
Acknowledgments
In Gabon, we thank P. Posso, Director of the Tropical Ecology Research Institute (IRET)
for permission to research and collect specimens at the Ipassa Plateau Reserve research
station near Makokou, Gabon. We also thank J. D. Mbega, Director of the Agronomy and
Forestry Research Institute (IRAF) for assistance with field work. At the AMNH we thank
M. Stiassny for her support for this study, R.A. Arrindel for assistance with radiographing
specimens, and B. A. Brown and D. R. Batista for curatorial assistance. K.R. Luckenbill
radiographed specimens at the ANSP. V. M. Wong illustrated the holotype. The late G.

SULLIVAN & HOPKINS
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ZOOTAXA Teugels provided the initial inspiration for this project. This work was funded by an H.R.
Axelrod postdoctoral fellowship at the AMNH to JPS and NSF 0108372 to CDH.
References
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