Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics
Author
Craig, Jack M.
Author
Malabarba, Luiz R.
Author
Crampton, William G. R.
Author
Albert, James S.
text
Zootaxa
2018
2018-02-13
4379
1
47
73
journal article
30758
10.11646/zootaxa.4379.1.3
865903f4-a866-4708-88df-26f5df06baa2
1175-5326
1172318
03F8692B-1887-4A18-AA23-B9BC20DD1426
Gymnotus inaequilabiatus
Valenciennes, 1847
Figure 15
,
Table 2
Material
examined:
Argentina
:
MACN
5979
,
250
mm,
Rosario
,
Río La Plata
(~
32°56’S
,
060°38’W
)
;
MLP
3353
,
250
mm,
Misiones
,
Río
Paraná
(~
26°49’S
,
055°00’W
)
; MNHN 4615 (neotype),
920 mm
(
600 mm
according to the original description,
850 mm
according to the label), Argentina, Buenos Aires, Rio de La Plata (~30°40’S, 058°30’W according to MNHN database or ~34°37’S, 058°23’W).
Brazil
,
Mato Grosso
:
LBP 12616, ~
650 mm
,
Corumbá
,
Rio Paraguai
drainage,
Rio Cuiabá
(~
18°09’S
,
057°33’W
)
.
Brazil
,
Mato Grosso
do Sul
:
MCP
15818
,
535
mm,
Rio Paraguai
near
Cáceres
;
USNM
1643
,
791
mm,
Rio
Paraguai
drainage (~
17°53’S
,
057°29’W
)
.
Brazil
,
Rio
Grande do Sul
:
MCP 6059
(3),
173–355 mm
,
Iraí
,
Rio Uruguai
drainage,
Sanga das Águas Frias
,
100 m
from
Rio Uruguai
(
27°12’00”S
, 053°16’60”W)
;
MCP
6956
,
602
mm, Rio
Uruguai
at
Santana Velha
, near
Uruguaiana
(~
29°45’S
,
057°50’W
)
;
MCP
19552 (3),
145–336 mm
,
Rosário do Sul
, pool next to
Olaria
in the floodplain along
Rio Santa Maria
,
North
side of BR290 (30°14’16”,
054°53’33”W
)
;
MCP
31177
,
560
mm,
Roque Gonzales
, Rio
Uruguai
drainage,
Rio Ijuí
near small hydroelectric power station (
PCH
)
Pirapó
(~
28°30’S
,
055°10’W
)
;
MCP
39375
,
550
mm, same locality as
MCP
31177
; UFRGS
14457, 498 mm
, (~27°11’S, 053°06’W).
Brazil
,
Santa Catarina
:
MCP
19044
,
440
mm,
Itá
,
Rio Uruguai
,
Rio do Engano
, road
between Itá and
Seara
(27°08’60”S,
52°13’00”W
)
;
MCP
20683
,
410
mm,
Itapiranga
, Rio
Uruguai
, near
Fortaleza
(
27°11’42”S
,
053°38’34”W
)
.
Brazil
,
São Paulo
:
MZUSP 22246
(3),
130–282 mm
,
Represa do Boa
,
Corumbataí
,
Rio
Paraná
drainage,
Rio Tietê
(~
21°46’S
,
048°58’W
)
;
MZUSP
22862
,
238
mm,
Corumbataí
, Rio
Paraná
drainage,
Rio Tietê
,
Lagoa Ponte Seca
(~
21°46’S
,
048°58’W
)
;
MZUSP
46001
,
998
mm, Rio
Paraná
drainage,
Porto Primavera
(~
22°31’S
,
053°10’W
).
Diagnosis.
Gymnotus inaequilabiatus
differs from all sympatric members of the
Gymnotus tigre
clade (
G. paraguensis
) on the following characters: 1, more precaudal vertebrae (
45 in
all specimens vs. 32–35, median 34); 2, fewer ventral lateral-line rami (VLR 23–38, median 32 vs. 49–55, median 50).
Gymnotus inaequilabiatus
further differs from sympatric
Gymnotus
species on the following characters: 1, total length (max.
998 mm
vs. max.
419 mm
in
G. c. australis
and max.
305 mm
in
G. cuia
the next two largest species); 2, a color pattern characterized by 21–29, mode 22 obliquely-oriented, chocolate-colored bands in juveniles (<
400 mm
), replaced in adults by large, irregular spots and blotches.
Description:
Morphometric and meristic data in
Table 1
. Sexually monomorphic, including in breeding condition. Total length to
1 m
.
Morphological maturity at roughly
130 mm
. Scales rounded to slightly ovoid on anterior two thirds of body, ovoid on posterior one third. Gape large in mature specimens, to or beyond posterior nares. Mouth superior with lower jaw longer than upper, rictus decurved. Chin especially fleshy and protuberant with fleshy pad of electrosensitive organs overlying tip of snout and oral jaws. Anterior narial pore partially to entirely included within gape in narial fold. Anterior nares large, subequal to eye diameter. Circumorbital series ovoid. Ethmoid region broad between anterior nares, with rounded anterior margin. Eye position lateral, lower margin of eye dorsal or horizontal to rictus. Premaxilla with 11 teeth disposed in single row along outer margin, arrow-head shaped anteriorly, conical posteriorly. Straight median margin of premaxilla. Maxilla-palatine articulation near anterior tip of endopterygoid. Maxilla vertical, rod-shaped, narrow distally with a straight ventral margin, length equal to roughly width of 4–6 dentary teeth. Dentary with one row of 12–15 teeth, none arrow-head shaped anteriorly. Posterodorsal and posteroventral dentary processes abut at midlength. Dentary posteroventral process shorter than posterodorsal, narrow distally. Dentary ventral margin lamella narrow, depth less than posterior process. Opercle dorsal margin straight to slightly convex. Dorsal opercular process lamellar or rugose, crest absent or small, posterior margin entirely smooth, without spines or processes. Preopercle with anteroventral notch, posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entire, median shelf large, more than one-half width of symplectic. Metapterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base shorter than length, curved, tip simple. Interopercle dorsal margin ascending process broad. Subopercle dorsal margin concave. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin square. Anguloarticular process short, extending beyond ventral margin of dentary. Mandible long, extended, length greater than twice depth. Trigeminal nerve canals divided within the hyomandibula. Posterior lateral line fenestra not contacting posterodorsal margin of hyomandibula. Cranial fontanels closed in juveniles and adults. Frontal shape broad, width at fourth infraorbital greater than that of parietal, anterior margin of straight, continuous with margins of adjacent roofing bones, postorbital process broad, more than two times width of supraorbital canal. Lateral ethmoid absent. Parietal rectangular, length less than width. Parasphenoid anteroventral portion robust, extending ventral to lateral margin of parasphenoid, posterior processes narrow. Prootic foraminae separate for cranial nerves Vp and
V2–3
+VII. Adductor mandibula muscle undivided at insertion, intermuscular bones absent. All basibranchials unossified. Gill rakers not contacting gill bar. Pectoral with 13–21 (mode 19) rays, medial radial large. Mesocoracoid elongate, length more than four times width.
Cleithrum broad, ventral margin curved, anterior limb long, more than 1.8 times ascending limb, deeply incised on its anteroventral margin, without large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity of long, with 45 precaudal vertebrae. Rib five robust along its entire extent, less than three times width of rib six. Hemal spines present. Displaced hemal spines absent. Length anal-fin pterygiophores equal to or longer than hemal spines. Anal fin with 214–390 (median 370) rays. Lateral line ventral rami 23–38 (median 32). Caudal appendage short, less one-half length of pectoral fin. Single hypaxial electric organ along entire ventral margin of body. Four rows of electroplates near caudal insertion of anal fin.
Color in Alcohol:
Bands, spots and blotches irregular in shape, width and color, on specimens and among individuals. Ground color tan to yellow. In juveniles (
250–400 mm
), obliquely-oriented, chocolate-colored bands with wavy, irregular margins on lateral surface from nape and to tip of caudal appendage, occurring singly or as band-pairs, increasingly divided and irregular with size (21–29 mode 22). In adults, bands replaced by spots and blotches. Head never banded, spotted, or blotched, dark grey dorsally grading to lighter grey ventrally. Numerous chromophores speckled over branchiostegal membranes and ventral surface of head. Pectoral-fin rays brown, interradial membranes hyaline. Anal-fin membrane with irregular broken horizontal stripes on posterior 20%.