A New Miniature Species of Serrapinnus (Characiformes: Characidae) from the Upper Rio Araguaia, Brazil

Abstract

During an expedition to the headwaters of the Rio das Mortes, Mato Grosso, in the Brazilian Shield, a new species of Serrapinnus was found. The new species is distinguished from all congeners by having eight branched dorsal-fin rays, three premaxillary teeth, and a conspicuous dark stripe extending from the eye to the caudal-fin median rays. Among congeners, a similar coloration pattern is present only in S. sterbai, but in that species the stripe usually originates posterior to the eye, on the opercle, and extends to the caudal-fin median rays. In the single locality where the new species was captured, it occurs syntopically with Hyphessobrycon cf. vilmae, another small characid in which a dark midlateral stripe is quite remarkable. Both species were captured together and were observed in situ swimming in mixed shoals. Thus, it is suggested that both species increase their individual chances of survival through the strategy of ‘‘protective association’’ via numeric mimicry.

Full text

A New Miniature Species of Serrapinnus (Characiformes: Characidae) from
the Upper Rio Araguaia, Brazil
Fernando C. Jerep
1
, Fernando C. P. Dagosta
2
, and Willian M. Ohara
3
During an expedition to the headwaters of the Rio das Mortes, Mato Grosso, in the Brazilian Shield, a new species of
Serrapinnus was found. The new species is distinguished from all congeners by having eight branched dorsal-fin rays,
three premaxillary teeth, and a conspicuous dark stripe extending from the eye to the caudal-fin median rays. Among
congeners, a similar coloration pattern is present only in S. sterbai, but in that species the stripe usually originates
posterior to the eye, on the opercle, and extends to the caudal-fin median rays. In the single locality where the new
species was captured, it occurs syntopically with Hyphessobrycon cf. vilmae, another small characid in which a dark
midlateral stripe is quite remarkable. Both species were captured together and were observed in situ swimming in
mixed shoals. Thus, it is suggested that both species increase their individual chances of survival through the strategy of
‘‘protective association’’ via numeric mimicry.
Durante uma expedi¸ca
˜oa
`s cabeceiras do Rio das Mortes, Mato Grosso, no Escudo Brasileiro, uma esp´
ecie nova de
Serrapinnus foi encontrada. A esp´
ecie nova distingue-se de todas as suas congˆ
eneres por apresentar oitos raios
ramificados na nadadeira dorsal, trˆ
es dentes no premaxilar e uma faixa escura bem marcada que se estende do olho at ´
e
os raios medianos da nadadeira caudal. Entre as congˆ
eneres, um estado semelhante s ´
o esta
´presente em S. sterbai, por´
em
nesta esp´
ecie a faixa geralmente se origina posteriormente ao olho, sobre o op´
erculo, e se estende at´
e os raios medianos
da nadadeira caudal. No ´
unico local onde a esp´
ecie nova foi capturada, a mesma ocorre sintopicamente com
Hyphessobrycon cf. vilmae, um outro carac´
ıdeo de pequeno porte cuja presen¸ca de uma faixa escura lateral ´
e bastante
marcante. As duas esp´
ecies foram capturadas juntas e foi observado in situ que nadam em cardumes mistos. Assim,
sugere-se que ambas as esp´
ecies aumentem suas chances individuais de sobrevivˆ
encia atrav´
es da estrat´
egia de
‘‘associa¸ca
˜o protetora’’ via mimetismo num´
erico.
SERRAPINNUS includes 15 valid species (Jerep et al.,
2016; Eschmeyer et al., 2017) widely distributed
throughout the Amazon, Orinoco, and Guyanese
drainages, Parana
´-Paraguay-La Plata system, and coastal river
basins in Brazil (Malabarba, 2003; Zarske, 2012; Jerep and
Malabarba, 2014; Malabarba and Jerep, 2014; Jerep et al.,
2016). All species are small-sized and, mostly, with an
incomplete lateral line, except S. heterodon (Eigenmann,
1915). Mature males possess hypertrophied anal-fin-ray-
bearing hooks (shared with some genera of the tribe
Cheirodontini) and present small variation of coloration,
usually light overall body background and a dark rounded
spot—more frequently referred to as a blotch—on the caudal
peduncle. Additionally all species of the group have a
remarkable sexual dimorphism involving the hypertrophy
of the caudal-fin procurrent rays. Besides supporting the
monophyly of the group (Malabarba, 1998; Jerep and
Malabarba, 2014; Malabarba and Jerep, 2014; Jerep et al.,
2016), modifications of those rays also offer important
characters for the delimitation of species.
As pointed out by Malabarba and Jerep (2014), the
cheirodontines from the Rio Tocantins-Araguaia basin only
began to be known in 2012 with the descriptions of
Ctenocheirodon pristis Malabarba and Jerep, 2012 and Serra-
pinnus sterbai Zarske, 2012 (Malabarba and Jerep, 2012;
Zarske, 2012). Later, Malabarba and Jerep (2014) revised the
species of Serrapinnus occurring in that basin and described
three new taxa (Serrapinnus aster Malabarba and Jerep, 2014;
S. lucindai Jerep and Malabarba, 2014; and S. tocantinensis
Malabarba and Jerep, 2014). All five species of cheirodontines
occurring in the Rio Tocantins-Araguaia are endemic to the
basin, highlighting the high degree of endemism in the
region. Herein, a new species of Serrapinnus is described based
on specimens collected during an expedition to the head-
waters of the Rio das Mortes, Rio Araguaia basin, Mato
Grosso, corroborating the poor knowledge on the fish fauna
of that basin.
MATERIALS AND METHODS
Counts and measurements were taken from the left side of
the specimens whenever possible, following Fink and Weitz-
man (1974) and Jerep and Malabarba (2014). Measurements
were made with a digital caliper under a microscope and are
presented as percents of standard length (SL) or head length
(HL) for subunits of the head. Vertebral count included the
four vertebrae of the Weberian apparatus as separate
elements, and the terminal centrum counted as a single
element following Weitzman and Malabarba (1999). Counts
of teeth, cusps, gill-rakers on first branchial arch, supra-
neurals, procurrent caudal-fin rays, and vertebrae were taken
from cleared and stained (CS) specimens prepared according
to Taylor and Van Dyke (1985). In the description, counts are
followed by their frequency in parentheses, and holotype
values are marked with an asterisk. Photographs of jaws and
teeth, ventral procurrent caudal-fin rays, and anal fin were
taken from CS specimens in a microscope camera with focus
stacking. Color in life was described based on photographs
1
Museu de Zoologia da Universidade Estadual de Londrina, Programa de P´
os-Gradua¸ca
˜oemCi
ˆ
encias Biol´
ogicas, Departamento de Biologia
Animal e Vegetal, Centro de Ciˆ
encias Biol´
ogicas, 86057-970 Londrina, PR, Brazil; Email: fjerep@gmail.com Send reprint requests to this
address.
2
Faculdade de Ciˆ
encias Biol´
ogicas e Ambientais, Universidade Federal da Grande Dourados, Rodovia Dourados–Itahum, Km 12–Cidade
Universita
´ria, 79804-970 Dourados, MS, Brazil; Email: ferdagosta@gmail.com.
3
Museu de Zoologia da Universidade de Sa
˜o Paulo, Avenida Nazar´
e, 481, Ipiranga, Caixa Postal 42494, 04218-970 Sa
˜o Paulo, SP, Brazil; Email:
willianmohara@gmail.com.
Submitted: 6 July 2017. Accepted: 9 November 2017. Associate Editor: R. E. Reis.
Ó2018 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CI-17-653 Published online: 6 March 2018
Copeia 106, No. 1, 2018, 180–187

and direct observations in the field. Osteological nomencla-
ture follows Weitzman (1962) and Zanata and Vari (2005).
Institutional abbreviations follow Sabaj (2016).
Serrapinnus malabarbai, new species
urn:lsid:zoobank.org:act:D57E1CEC-E45C-4B72-BA95-
ED2062B11D58
Figures 1–5A, Table 1
Holotype.—MZUSP 117117, 20.2 mm SL, male, Brazil, Mato
Grosso, Primavera do Leste, Rio Araguaia basin, Rio Suspiro,
tributary to Rio das Mortes, 14852030.9200 S, 54805001.4000 W, F.
C. P. Dagosta and W. M. Ohara, 17 June 2014.
Paratypes.—Same data as the holotype: MZUEL 17778, 4,
20.2–20.3 mm SL (2 CS, 19.8–20.1 mm SL); MZUSP 118679,
17, 18.5–24.5 mm SL (2 CS, 19.2–20.1 mm SL).
Diagnosis.—Serrapinnus malabarbai differs from all congeners,
except S. sterbai, by the possession of a well-defined dark
midlateral stripe on body. Additionally, S. malabarbai differs
from all its congeners by three autapomorphic features: eight
branched rays in the dorsal fin (vs. nine branched dorsal-fin
rays), three premaxillary teeth (vs. four or more teeth in the
premaxilla), and inconspicuous caudal-peduncle spot (vs.
conspicuous caudal-peduncle spot, even when crossed by a
longitudinal dark stripe). It can be readily distinguished from
S. sterbai by having the midlateral dark stripe starting over
the eye (vs. midlateral dark stripe starting over the opercle).
Description.—Morphometric data of holotype and 21 para-
types of Serrapinnus malabarbai in Table 1. Body slightly
elongated and compressed; greatest body depth at vertical
through dorsal-fin origin. Largest specimen examined 24.5
mm SL. Snout slightly rounded in lateral view. Dorsal profile
of head slightly convex from snout to vertical through
posterior border of pupil, slightly concave from that point to
distal tip of supraoccipital bone. Predorsal region profile
convex from posterior tip of supraoccipital to dorsal-fin
origin. Dorsal-fin base slightly convex, descending posteri-
orly. Dorsal profile from last dorsal-fin ray to adipose-fin base
straight to slightly convex, and ventrally arched in sexually
dimorphic males. Dorsal profile from adipose-fin origin to
caudal-fin origin concave. Ventral profile of head and
anterior region of body slightly convex from mouth to
pelvic-fin origin; straight to slightly convex from that point
to anal-fin origin of females, usually concave in sexually
dimorphic males. Anal-fin base straight to slightly concave;
slightly convex anteriorly and concave medially in dimor-
phic males. Ventral profile of caudal peduncle straight to
slightly concave; distal tip of hypertrophied ventral procur-
rent caudal-fin rays exposed in males.
Mouth small and terminal, opening at horizontal line
through middle of eye pupil. Maxilla short, posteroventrally
angled, posterior end reaching vertical between first and
second nostril and surpassing ventrally horizontal between
ventral margin of pupil and ventral margin of eye. Teeth
compressed and pedunculated, distally expanded, all similar
in shape. Premaxilla with 3(4) teeth aligned in single row
with 6–7 cusps. Maxilla with 1(3) or 2(1) teeth with one, five
or six cusps. Dentary with 3(4) large teeth with five or seven
cusps, followed posteriorly by one or two smaller teeth,
decreasing in size and cusp number posteriorly, with five to
one cusps. All teeth with midcentral cusp slightly longer and
wider than lateral ones (Fig. 2).
Pectoral-fin rays i,8*(9) or i,9(13). Pectoral fin not reaching
pelvic-fin origin. Pelvic-fin origin anterior to vertical through
dorsal-fin origin. Dorsal-fin rays ii,8*(22). First unbranched
dorsal-fin ray shorter than half length of second unbranched
ray. First branched ray slightly longer than second un-
branched ray, following branched rays gradually decreasing
in size posteriorly. Pelvic-fin rays i,6*(20) or i,7(2). Un-
branched pelvic-fin ray longer than first branched ray in
dimorphic males, forming short filament. Pelvic-fin rays with
acute bony hooks in males, less numerous on unbranched
ray. One or two unpaired hooks ventromedially placed per
lepidotrichia, associated with hypertrophied soft tissue. Anal-
fin origin posterior to vertical through base of last dorsal-fin
ray. Anal-fin rays iii*(22)13(1), 14(7), 15*(12), or 16(2). Anal-
fin distal profile slightly pointed on anterior lobe and
concave posterior to that point; slightly rounded on anterior
lobe and deeply concave posterior to that point in sexually
dimorphic males. First branched anal-fin ray longer, remain-
ing rays decreasing in size posteriorly. Dimorphic males with
acute, retrorse hooks on posterior border and posterior
branches of anal-fin rays, posterolaterally arranged on last
unbranched to 5
th
–6
th
branched rays (Fig. 3). One to three
unpaired hooks per ray segment of hemitrichia. Hooks
mostly distributed along first and second third of anal-fin
ray length. Hook-bearing rays with segments and branches
progressively fused according to degree of maturation of
males. Hypertrophied soft tissue associated with hook-
bearing anal-fin rays. Adipose-fin origin at vertical through
base of penultimate or last anal-fin ray. Principal caudal-fin
rays 19*(22). Dorsal procurrent caudal-fin rays 13(4); ventral
procurrent caudal-fin rays 11(2), 12(1), or 13(1). Procurrent
rays hypertrophied in sexually dimorphic males, expanded
on sagittal plane, resulting in exposed sharp keel. Hypertro-
phied ventral procurrent rays straight, proximal end acute,
expanding distally, distal end spatulate (Fig. 4).
Scales cycloid, 32(10), 33*(9), 34(2), or 35(1) on lateral line
longitudinal series. Pored scales on lateral line 6(1), 7*(7),
8(7), or 9(7); predorsal scales 10(3), 11*(9), or 12(10); scale
rows between lateral line and dorsal-fin origin 5*(22); scale
rows between lateral line and pelvic-fin origin 4*(22);
circumpeduncular scale rows 12*(18) or 13(4). Scales sheath
over base of anterior anal-fin rays 8*(3), 9(11), or 10(8).
Supraneurals 4(1) or 5(3); precaudal vertebrae 16(4), caudal
vertebrae 18(4); branchiostegal rays 4(4); first gill arch with
2(4) rakers on hypobranchial, 7(1), 8(2), or 9(1) rakers on
ceratobranchial, 1(4) raker on intermediate cartilage, and 4(1)
or 5(3) rakers on epibranchial.
Pseudotympanum well developed, composed of one
muscular hiatus delimited medially by anterior swimbladder
chamber and laterally by adipose tissue and skin. Muscular
hiatus pentagonal and bordered anteriorly and posteriorly by
first and second pleural ribs, respectively, dorsally by lateralis
superficialis muscle, anteroventrally by obliquus superioris
muscle, and posteroventrally by obliquus inferioris muscle.
Color in alcohol.—Overall background body color yellow (Fig.
1). Infraorbital, opercular, and gular areas retaining some
guanine. Small dark chromatophores concentrated on dorsal
region and upper jaw. Head with numerous large melano-
phores on dorsal region. Dorsal half of opercle and region of
5
th
and 6
th
infraorbitals with large, sparse chromatophores.
Dark midlateral stripe on body, extending from anterior
margin of eye to base of median caudal-fin rays. Midlateral
stripe diffuse on infraorbital and opercular series, and slightly
expanded on caudal peduncle not forming distinct caudal-
Jerep et al.—New Serrapinnus from the Rio das Mortes 181

peduncle spot. Humeral blotch absent. Humeral region with
triangular darkened area under midlateral stripe due to
presence of pseudotympanum. Dorsum more densely pig-
mented than ventral region of body due to higher number of
dark chromatophores; usually forming reticulated pattern on
first two or three horizontal scale rows by concentration on
posterior margin of scales. Clear area between midlateral
stripe and second or third horizontal scale rows. Body lacking
chromatophores ventral to midlateral band, except by
concentration of dark chromatophores above anal fin.
Dorsal, anal, pectoral, pelvic, and caudal fins scattered with
melanophores along anterior and posterior edges of lepido-
trichia. Adipose fin with sparse, dark chromatophores.
Color in life.—Overall dark pigmentation as described above.
Infraorbitals 2, 3, and 4, opercular series, and abdominal
region covered with guanine. Upper lip and anterior half of
dentary pale yellow. Top of head and dorsum dark brown.
Eye with dark pigmentation crossing horizontally; dorsal
portion yellow to blue, lower portion clear, with silvery hue.
Dark midlateral stripe distinctly conspicuous. Yellow to
golden stripe parallel and immediately above to dark mid-
lateral stripe extending from above opercle to caudal
peduncle. Dorsal, adipose, and anal fins pale yellow. Pectoral
and pelvic fins hyaline. Base of median caudal-fin rays dark,
base of remaining caudal-fin rays yellow (Fig. 5).
Sexual dimorphism.—Males above 19.3 mm SL with bony
hooks on the ventro-medial margin of all pelvic-fin rays, one
or two unpaired hooks per ray lepidotrichia, and less
numerous on unbranched ray; bony hooks on the postero-
lateral margin of the last unbranched and first 5–6 branched
anal-fin rays, with one to three unpaired hooks per ray
lepidotrichia and less numerous on 6
th
branched ray; anal-fin
rays bearing hypertrophied bony hooks, sometimes with
fused lepidotrichia, slightly expanded in sagittal plane (Fig.
Fig. 1. Serrapinnus malabarbai, Rio Suspiro, tributary to Rio das Mortes, Primavera do Leste, Mato Grosso, Brazil. (A) MZUSP 117117, holotype,
male, 20.2 mm SL; (B) MZUSP 118679, paratype, female, 24.5 mm SL.
182 Copeia 106, No. 1, 2018

3); ventral procurrent caudal-fin rays hypertrophied, ventral-
ly exposed, parallel to each other, spatulated, and forming a
ventral keel on the caudal peduncle (Fig. 4); caudal peduncle
slightly arched ventrally in most sexually dimorphic pre-
served males. No gill-gland on the first branchial arch of
males or females (sensu de Oliveira et al., 2012).
Distribution.—Serrapinnus malabarbai is so far known only
from its type locality, a stream tributary to Rio Suspiro, upper
Rio das Mortes, Rio Araguaia drainage, Rio Tocantins basin,
Primavera do Leste, Mato Grosso, Brazil (Fig. 6).
Etymology.—The specific epithet malabarbai is in honor of
Luiz Roberto Malabarba (UFRGS), in recognition of his great
contribution to our knowledge on the Cheirodontinae and
other Neotropical freshwater fishes. A genitive noun.
Habitat and ecological notes.—The type locality of Serrapinnus
malabarbai is a small, clear water stream 1.5–4 m wide and
0.3–1.5 m deep, with swift water current, and sandy bottom.
The specimens were captured in a shallow (0.2–0.6 m), and
narrow (0.5–1.5 m) temporary channel. Individuals of S.
malabarbai were captured syntopically with Hyphessobrycon
cf. vilmae G´
ery, 1966, Hyphessobrycon loweae Costa and G´
ery,
1994, Characidium mirim Netto-Ferreira, Birindelli, and
Buckup, 2013, Characidium sp., and Hemigrammus sp.
DISCUSSION
Relationships.—Serrapinnus malabarbai possesses all synapo-
morphies of the Cheirodontinae (sensu Malabarba, 1998) and
both synapomorphies proposed by the same author for the
genus (i.e., the caudal peduncle conspicuously arched
ventrally in preserved dimorphic males, and the main axis
of the ventral procurrent caudal-fin rays not supported by the
parhypural, being perpendicular to the longitudinal axis of
the body, whereas the most anterior elements are anteriorly
directed). Serrapinnus malabarbai also has an incomplete
lateral line, a condition shared with most congeners except
by S. heterodon, and occasionally by some specimens of S.
sterbai and S. tocantinensis.
Among the species of Serrapinnus, the coloration of S.
malabarbai roughly resembles the pattern observed in S.
sterbai, a sympatric, but not syntopic, species from the Rio
Araguaia basin. It is composed of a dark midlateral stripe
extending along the body and reaching the caudal peduncle
and median caudal-fin rays. Nevertheless, the stripes on both
species differ in some details such as the stripe crossing the eye
in S. malabarbai (not reaching the eyes anteriorly in S. sterbai).
Fig. 2. Clear and stained jaws showing right side of premaxilla, maxilla,
and dentary of Serrapinnus malabarbai, MZUEL 17778, paratype, male,
19.8 mm SL. Lateral view, anterior to left.
Fig. 3. Anal fin of a dimorphic male with hypertrophied anal-fin rays
and hook shape and arrangement of Serrapinnus malabarbai, MZUEL
17778, paratype, 19.8 mm SL. Lateral view, anterior to left. Scale bar: 1
mm.
Fig. 4. Ventral procurrent caudal-fin rays of Serrapinnus malabarbai,
MZUEL 17778, paratype, male, 19.8 mm SL. Lateral view, anterior to left.
Scale bar: 1 mm.
Jerep et al.—New Serrapinnus from the Rio das Mortes 183

Fig. 5. Coloration in life immediately after capture. (A) Serrapinnus malabarbai, MZUSP 118679, paratype; (B) Hyphessobrycon cf. vilmae (adipose
fin is missing).
Table 1. Morphometric data of Serrapinnus malabarbai. Female (F) and male (M) range, mean, and standard deviation (SD). Male data include
values of the holotype.
Characters Holotype M Min Max Mean SD F Min Max Mean SD
Standard length 20.2 11 19.3 21.6 20.4 0.7 11 18.5 24.5 20.2 1.5
Percents of standard length
Head length (HL) 24.4 11 23.3 24.7 24.1 0.4 11 21.2 24.8 23.9 1.0
Bony head length 25.9 11 23.2 25.9 24.4 0.7 11 23.1 25.1 24.1 0.7
Snout-anal fin distance 64.4 11 60.2 66.8 64.5 1.7 11 65.0 68.9 66.9 1.3
Snout-dorsal fin distance 53.9 11 49.3 53.9 51.9 1.4 11 50.5 54.5 52.8 1.4
Snout-pelvic fin distance 47.3 11 42.6 47.3 45.2 1.4 11 43.5 46.7 45.1 1.0
Snout-pectoral fin distance 25.6 11 22.9 26.3 24.7 1.2 11 23.5 26.3 24.8 0.9
Dorsal-fin base length 12.9 11 10.8 12.9 12.0 0.8 11 10.9 14.0 11.9 0.9
Anal-fin base length 15.3 11 15.3 21.8 18.9 1.8 11 19.1 21.4 20.4 0.8
Caudal-peduncle length 16.7 11 15.2 19.2 16.9 1.2 11 14.6 17.6 15.7 0.8
Caudal-peduncle depth 13.4 11 11.9 13.4 12.4 0.5 11 9.7 11.6 10.5 0.5
Body depth at dorsal fin 30.2 11 26.9 30.9 28.7 1.3 11 28.6 32.8 30.4 1.3
Dorsal-fin length 26.7 11 23.3 27.5 25.8 1.4 11 21.5 26.9 25.0 1.9
Anal-fin length 18.3 11 16.9 20.2 18.9 1.0 11 16.8 23.0 18.8 1.6
Pelvic-fin length 19.6 11 16.1 20.1 18.2 1.4 11 14.3 18.0 17.0 1.1
Pectoral-fin length 20.0 11 17.1 21.6 20.0 1.2 11 15.7 18.4 17.0 0.8
Percents of head length
Snout length 25.8 11 23.1 27.5 24.8 1.3 11 22.0 28.8 23.6 1.9
Upper jaw length 24.4 11 21.5 24.6 23.0 1.1 11 19.0 27.4 22.6 2.5
Horizontal orbit diameter 42.1 11 39.2 43.6 41.7 1.2 11 38.7 46.4 42.6 2.2
Interorbital width 33.5 11 31.5 34.7 33.2 1.1 11 28.9 35.6 31.6 1.9
184 Copeia 106, No. 1, 2018

Besides the slight differences in color pattern, these species
greatly differ from each other in several other morphological
characters: eight branched dorsal-fin rays (vs. nine), 14–15
branched anal-fin rays (rarely 13 or 16 vs. 17–21, rarely 16);
dimorphic males bearing bony hooks on the first five or six
anal-fin rays (vs. hooks present on seven or eight rays); and
the hypertrophied ventral caudal-fin rays in dimorphic males
being spatulate, arranged parallel to each other, forming a
straight posteriorly descending keel (vs. ventral procurrent
caudal-fin rays rod-shaped and arranged in a semi-circle).
Despite the resemblance of the color pattern shared by S.
malabarbai and S. sterbai, the proposition of a close relation-
ship between both species is considered premature at this
time, and should be, instead, tested in a cladistic framework.
Miniaturization.—Weitzman and Vari (1988) proposed two
main size-related characters that should be used to define
miniature fish species: maximum length of 26 mm SL or
sexual maturation under 20 mm SL. Although arbitrary, these
standards have been used as a preliminary step to the
classification of miniature fishes in several studies (Britz,
2003; Kottelat et al., 2006; Toledo-Piza et al., 2014).
Within Cheirodontinae (sensu Malabarba, 1998; B¨
uhrnheim
et al., 2008), miniaturization has been recorded in seven species
(Toledo-Piza et al., 2014), all from the tribe Cheirodontini:
Amazonspinther dalmata B¨
uhrnheim, Carvalho, Malabarba, and
Weitzman, 2008, Nanocheirodon insignis (Steindachner, 1880),
Serrapinnus gracilis (G´
ery, 1960), Serrapinnus kriegi (Schindler,
1937), Serrapinnus littoris (G´
ery, 1960), Serrapinnus malabarbai,
and Spintherobolus broccae Myers, 1925. Based on the hypoth-
esis of relationship within the tribe proposed by B¨
uhrnheim et
al. (2008), events of miniaturization seem to have occurred
independently in Amazonspinther,Nanocheirodon, and in a
single species of Spintherobolus. Notwithstanding, further
relationship studies are needed to evaluate how the reduction
in size evolved in four of the 16 species of Serrapinnus.
Besides the small size (18.5–23.5 mm SL vs. maximum
length up to 26.0 mm SL), Serrapinnus malabarbai also
presents reduction in the number of branched rays in the
dorsal (eight vs. nine), anal (13–15, rarely 16 vs. more than
16), and pelvic (six vs. seven, rarely six) fins, and number of
circumpeduncular scale series (12–13 vs. 14, rarely 12), which
are frequently considered paedomorphic morphological
features commonly observed in miniature species.
The dentition in S. malabarbai shows another remarkable
reduction. In other species of Serrapinnus the number of jaw
teeth range from four to six in the premaxilla, two to four
large teeth in the maxilla, and four to eight large most
anterior teeth in the dentary. Although S. malabarbai presents
a generalized condition regarding the number of tooth cusps
(five to seven), the number of teeth is the lowest among its
congeners with only three premaxillary teeth, one large
maxillary tooth, and three large most anterior dentary teeth.
Other characters usually observed in miniaturized species
are reductions in the laterosensory canal system and size and
number of ossifications on head and body (Weitzman and
Vari, 1988). Serrapinnus malabarbai has a reduction of the
infraorbital bone series with the absence of the fourth to
Fig. 6. Map of central region of Brazil
showing the type locality (black star)
of Serrapinnus malabarbai in the Rio
das Mortes, Rio Araguaia basin.
Jerep et al.—New Serrapinnus from the Rio das Mortes 185

sixth infraorbital bones. In this condition, the infraorbital
laterosensory canal is enclosed in a fleshy structure or within
a reduced and poorly ossified tubular ossification.
Mimicry.—The freshwater ichthyofauna of South America is
rich in examples of mimicry, with cryptic fishes resembling
components of the habitat (leaves and branches; Lowe-
McConnell, 1969). In the Amazon basin, Monocirrhus poly-
acanthus Heckel, 1840, Tetranematichthys spp., Helogenes
marmoratus G¨
unther, 1863, and Steatogenys duidae (La Monte,
1929) are known to mimic dead leaves (Sazima et al., 2006);
Ammocryptocharax elegans Weitzman and Kanazawa, 1976
and Acestridium spp. mimic aquatic or submerged long leaves
of plants (Retzer et al., 1999; Zuanon et al., 2006); Amaralia
hypsiura (Kner, 1855) mimic bottom deposited plant seeds
(Roberts, 2015); and species of Farlowella mimic branches and
twigs. Likewise, observations of species of different genera
mimicking each other in mixed schools have been recorded
in several characids (i.e., G´
ery, 1960; Zanata et al., 2009;
Marinho and Birindelli, 2013), callichthyids/loricariids (Ax-
enrot and Kullander, 2003; Tencatt et al., 2014), and
crenuchids/erythrinids (Zanata and Ohara, 2015).
Aggregations of species sharing similar color patterns in
mixed shoals may enhance the survival of the individual
(Dafni and Diamant, 1984). Usually, those species present a
standardized coloration pattern to avoid visual disruption,
hampering the action of predators (Lowe-McConnell, 1987).
G´
ery (1960) defined this evolutionary mechanism as ‘‘pro-
tective association’’ when comparing heterotopic shoals of
characids. In rainforest creeks from French Guyana, G´
ery
(1960) mentioned as examples the association of Hyphesso-
brycon simulatus (formerly known as Pseudopristella simulata)
and Pristella maxillaris (Ulrey, 1894; f.k.a. Pristella riddlei) with
Hemigrammus unilineatus (Gill, 1858) and Hyphessobrycon
minor Durbin, 1909; Serrapinnus gracilis (f.k.a. Cheirodon
gracilis) with Hemigrammus guyanensis G´
ery, 1959 in inland
waters; and Serrapinnus littoris (f.k.a. Cheirodon littoris) and
Hemigrammus rodwayi Durbin, 1909 in coastal waters. All
above mentioned species possesses similar size and color
pattern: dark mark in the humeral and caudal peduncle
regions. Another putative example of mimicry involving
species of Serrapinnus has been mentioned to the Rio Paraguai
basin in the Pantanal, Brazil. In that region, numerous
heterotopic shoals including the characids S. calliurus
(Boulenger, 1900), S. kriegi,Aphyocharax nattereri (Steindach-
ner, 1882), the curimatid Curimatopsis myersi Vari, 1982, and
the callichthyid catfish Corydoras hastatus Eigenmann and
Eigenmann, 1888 have been observed in pools and lakes
(Myers, 1953; Sazima, 1986; Machado, 2003; FCJ, pers. obs.).
Serrapinnus malabarbai occurs syntopically with Hyphesso-
brycon cf. vilmae, a characid species with similar coloration
pattern (Fig. 5). The two species were observed in situ
swimming in mixed shoals and were captured together.
Thus, it is suggested that both species display numeric
mimicry and increase their individual chances of survival
through the strategy of ‘‘protective association.’’ Although
the hypothesis of mimicry between these species must be
empirically tested in the future, some interesting aspects of
that association can be highlighted. These include the
remarkable amount of details of color pattern shared by this
pair of species, such as the dark midlateral band, the
reticulated pattern on first two to three horizontal scale rows
with a clear region below, and the pigmentation pattern
above the anal fin. The latter is rare both in species of
Hyphessobrycon and Serrapinnus. The presence of a dark
midlateral stripe, as observed in the new species, is rare in
Serrapinnus, and even more unusual if the distribution of the
character among cheirodontines is considered. The color
pattern of S. malabarbai is perhaps the most peculiar among
the known species of the subfamily which may be an
indication that this has been established from the action of
selective pressures different from those of its congeners.
Indeed, Barlow (1972) suggested that the longitudinal stripes
have, in general, a confusing effect on predators. Interest-
ingly, the type locality of the new species has crystalline
water, allowing individuals to maintain visual contact with
each other. This factor seems to be crucial so that strategies
based on the premise of visual communication can evolve.
MATERIAL EXAMINED
In addition to the comparative material examined and listed
in Jerep et al. (2016), the following species were examined.
All from Brazil.
Serrapinnus calliurus (Boulenger, 1900): MZUEL 8146, 5, 19.8–
29.2 mm SL, Rio Miranda, tributary to the Rio Paraguay, Mato
Grosso do Sul.
Serrapinnus zanatae Jerep, Camelier, and Malabarba, 2016:
MZUSP 116000, 1, holotype, 36.8 mm SL, male, Rio Bananal,
tributary to the Rio Salinas in a dam nearby Salinas, Rio
Jequitinhonha basin, Salinas, Minas Gerais.
ACKNOWLEDGMENTS
We thank A. Datovo and M. Gianeti (MZUSP) for the loan of
specimens and for museum and technical support. Type
series was collected during an expedition funded by the
South American Characiformes Inventory (FAPESP 2011/
50282-7, http://ictio.saci.mz.usp.br). FCJ research is support-
ed by CNPq (453850/2014-6) and visit grant to MCP by
CNPq (504177/2012-5). FCPD research is supported by
FAPESP (2011/23419-1 and 2016/07246-3) and WMO is
supported by FAPESP (2013/22473-8).
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