Astyanax cocibolca Bussing 2008

Schmitter-Soto, Juan J., 2017, A revision of Astyanax (Characiformes: Characidae) in Central and North America, with the description of nine new species, Journal of Natural History (J. Nat. Hist.) 51 (21 - 24), pp. 1331-1424 : 1379-1380

Astyanax cocibolca Bussing 2008

( Figure 28 ; see original description for illustration of holotype)

Astyanax nasutus (non Meek 1907). Bussing 1976, 1998; Villa 1982.

Astyanax sp. Astorqui 1972 ; Lucena and Lucena 2002.

Diagnosis

Diagnosed from other Astyanax species in Nicaragua and neighbouring Costa Rica as follows: body slender, 36.4% SL or less (vs 33.9% SL or more); scales between lateral line and dorsal-fin origin, 6–8 (vs 8–9); caudal vertebrae, 19 (20 in A. nasutus ); caudal end of supraoccipital, concave (vs not concave); arms of premaxilla, subequal (dentigerous longer in A. bransfordii and A. nicaraguensis ); teeth in outer row of premaxilla, conical (vs usually tricuspid); only 1 dorsoposterior projection of metapterygoid (2 in A. bransfordii , A. nasutus and A. orstedii ); infraorbital III, semicircular (angled in A. bransfordii and A. orstedii ); lower pharyngeal plate, double (single in A. bransfordii , A. nasutus and A. nicaraguensis ). See also Bussing (2008).

Redescription

A species of Astyanax , subgenus Astyanax (i.e. with a complete predorsal series of scales).

Head profile straight; snout pointed; lips even, but mouth upturned. Pectoral fins rarely reach pelvic fin origin; anal and dorsal fins usually do not overlap. Lower lobe of caudal fin, longer.

D. 9–10; A. 24–27, modally 25 (from 22, in original description); pect. 10–14. Procurrent unsegmented dorsal rays on caudal fin, 9 or fewer. Gill rakers on first arch, 23–34 (according to Bussing 2008; in my sample, 27–31, modally 30); on lower limb, 16–19, modally 18. Scales on lateral line, 34–38, mean 35; predorsal scales, 9–12, modally 11; scale rows from lateral line to base of first dorsal-fin ray, modally 6, rarely 5; to base of pelvic fin, 5; to base of pectoral fin, modally 3, up to 3.5; circumpeduncular scales, 12–14. A long scaly sheath on anal-fin base, with imbricated scales. Nuptial tubercles simple, not on anal fin. Total vertebrae 32–33, modally 19 caudal. Detailed frequencies are given in Table 3.

Largest examined specimen, 59.9 mm SL. Body depth, 29–34% SL. Head length, 26–30% SL; orbital diameter, 30–37% HL; interorbital distance, usually narrow, 6.0– 9.1% SL. Further morphometric data are given in Table 4 (see also Bussing 2008).

Anterior fontanel long, convex-sided, sharp-tipped. Supraoccipital process in dorsal view, short, wide-based; slightly concave in lateral view. Vomer rostrally undulate. Premaxillary arms, subequal; 0–2 teeth. Highest tooth on dentary, fourth; posterior teeth, abruptly smaller. Dorsal edge of longer articular arm, straight. Maxillary, with a convex anteroinferior edge; 1–3 teeth. Quadrate, dorsal process not expanded. Metapterygoid, rostral arm much longer than ventral, 1 dorsorostral projection. Infraorbital II, triangular with an angled base; infraorbital III, inferoposteriorly semicircular; infraorbital IV, square, with a projection; contact between infraorbitals II and III, wide. Urohyal rostral end turned up, blunt; its ventrorostral edge convex, its ventral apex closer to caudal end; ceratohyal foramen oval; rostral vertices of ceratohyal angled, the ventral side undulate. Epibranchial III, insertion of uncinate process round, the distal segment of the main body straight. Upper pharyngeal bones, S-shaped; lower pharyngeal plate double, its caudal side straight. Dorsal side of hyomandibular, straight. Opercular dorsal edge, convex, with an angle; sides of dorsal half, parallel; posterior edge, dorsally undulate, ventrally straight; ventral tip, sharp. Interopercle, posterior edge, straight-convex, with a spine. Preopercle, anterodorsal edge, with a median convexity; ventral rim, straight; posteroventral edge, curved; only 1 canal at angle. Five predorsal bony elements; rostral edge of first pterygiophore curved. Coracoid with a single, deep interdigitation in suture to cleithrum, with 2 convexities, a concave caudal edge, a single posteroinferior spine. Caudad process of postcleithrum, digitiform. Dorsal and caudal tips of scaphium, truncate; dorsoposterior edge, slightly concave. Neural spines under dorsal fin, bent at tips. Postanal element, short. Seventh caudal vertebra from tail, with a haemal spine displaced caudad. Largest hypuric plate, rostral edge straight. Epuric plate on last neural spine, straight-sided.

Humeral spot, oval. Pigment on anal fin, sparse, concentrated distally. Caudal spot, both on peduncle and on fin rays.

Type material and depositor

Holotype LACM 56648–1 , Isletas de Granada, Lake Nicaragua, coll. J.D. Villa and M. Llobet, April 1966 . Paratypes: AMNH 30236 (20 specimens), LACM 56648–2 (50), UCR 24–16 (924), UCR 61–4 (301), 162–2 (238), 242–7 (4), UCR 536–8 (42), 538–6 (3), 539–6 (60), 540–5 (3), 547–6 (1), 552–3 (1), 553–2 (1), 1061–4 (2), 1075–8 (3) . For collection data, see original description.

Distribution

Endemic to Lake Nicaragua and tributaries, Nicaragua and Costa Rica ( Figure 28 ).

Remarks

Bussing (2008) found striking ecological differences between A. cocibolca and the other Astyanax present in Lake Nicaragua.

Figures

Figure 28. Map of lower Central America, showing distribution localities of Astyanax bransfordii, A. cocibolca, A. nasutus, A. nicaraguensis, A. orstedii and A. panamensis. Astyanax bransfordii and A. cocibolca co-occur in Lake Nicaragua. A larger symbol denotes the type locality (uncertain for A. nicaraguensis and A. panamensis).