Astyanax nasutus Meek 1907

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 : 1392-1393

Astyanax nasutus Meek 1907

( Figure 28 ; see Rosen 1972, for illustration of holotype)

Astyanax aeneus non Günther, partim. Astorqui 1972.

Deuterodon nasutus ( Meek 1907) : Lucena and Lucena 2002:113 et seq.

Diagnosis

Diagnosed from other Astyanax species in Nicaragua and neighbouring Costa Rica as follows: supraoccipital in dorsal view, long, narrow-based (shorter, wide-based in A. cocibolca , A. nicaraguensis and A. orstedii ); 2 dorsoposterior projections of metapterygoid (1 in A. cocibolca ); gill rakers on first arch lower arm, mean 11 (14 or more in A. nicaraguensis , A. bransfordii and A. cocibolca ); pelvic bone, proximal edge convex (straight in A. nicaraguensis ); caudal vertebrae 20 (19 in A. bransfordii ).

Redescription

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

Head profile straight; snout pointed to squarish; lower lip protruding; mouth terminal. Pectoral fins do not reach pelvic fin origin; anal and dorsal fins usually do not overlap. Lobes of caudal fin, subequal.

D. 9–10; A. 25–28; pect. 11. Procurrent unsegmented dorsal rays on caudal fin, 9 or fewer. Gill rakers on first arch, 19–22; on lower limb, 11–13. Scales on lateral line, 35–37; predorsal scales, 11; scale rows from lateral line to base of first dorsal-fin ray, 7–8.5; to base of pelvic fin, 5.5; to base of pectoral fin, 4. Nuptial tubercles, not seen. Total vertebrae 32–33, 20 caudal. See also Rosen (1972).

Largest examined specimen, 82.1 mm SL. Body depth 34–37% SL. Head short, 23–31% SL; orbital diameter, 29–30% HL (further morphometric data appear in Table 4; see also Meek 1907).

Anterior fontanel long, straight-sided, sharp-tipped. Supraoccipital process in dorsal view, long, narrow-based, angled in lateral view. Vomer rostrally undulate. Highest tooth on dentary, fourth; posterior teeth, not abruptly smaller. Dorsal edge of longer articular arm, straight. Maxillary, with a convex, notched anteroinferior edge; 4–6 teeth. Quadrate, dorsal process not expanded. Metapterygoid, rostral arm longer than ventral, 2 dorsorostral projections. Urohyal rostral end turned up, blunt; its ventrorostral edge convex, its ventral apex about equidistant between rostral and caudal ends; ceratohyal foramen comet-shaped; rostral vertices of ceratohyal angled, the ventral side straight. Upper pharyngeal bones, S-shaped; lower pharyngeal plate single, its caudal side straight. Dorsal side of hyomandibular, convex. Opercular dorsal edge, concave-convex; sides of dorsal half, parallel; posterior edge, dorsally and ventrally straight; ventral tip, rounded. Interopercle, posterior edge, straight-convex, with a spine. Preopercular anterodorsal edge, with a median convexity; ventral rim, straight; posteroventral edge, curved; 2 parallel canals at angle. Five predorsal bony elements. Caudad process of postcleithrum, digitiform, concave-sided. Dorsal tip of scaphium, truncate; caudal tip, sharp; dorsoposterior edge, slightly concave. Neural spines under dorsal fin, straight. 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, convex-sided.

Humeral spot, squarish; caudal spot, on peduncle and on fin. Colour in life, typical: ‘light olivaceous, a broad plumbeous band from upper edge of opercle to base of caudal, broadening into a caudal blotch’ ( Meek 1907, p. 108).

Type material and depositor

Holotype FMNH 5909, 125 mm SL, Lake Managua at Managua City, Nicaragua, coll. S.E. Meek. Paratypes: FMNH 5908 (12 specimens), 5910; same collection data as holotype; CAS 3949 (2 specimens), Lake Managua at Cisplaya, same collector and date.

Distribution

Endemic to Lake Managua and River San Juan, Nicaragua ( Figure 28 ) .

Remarks

Astyanax nasutus is Ornelas-García et al.’s (2008) clade VIII. Synonymised to A. aeneus s. l. by Astorqui (1972) only because of overlap in snout and maxillary length.

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).