Astyanax bacalarensis, Schmitter-Soto, 2017

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 : 1364-1367

Astyanax bacalarensis sp. nov.

( Figures 9 (b), 15, 22, 23)

Astyanax aeneus non Günther, part. Hubbs 1936, Greenfield and Thomerson 1997, Schmitter-Soto 1998, Schmitter-Soto et al. 2008, Miller et al. 2009.

Astyanax altior non Hubbs. Schmitter-Soto 1998.

Astyanax ‘Bacalar’, Schmitter-Soto 2016.

Diagnosis

Diagnosed from other Astyanax species in the Yucatan as follows: anal fin origin, never overlapping last dorsal-fin ray (always overlapping in A. altior ); head length, 28% SL or less (27% or more in A. altior ); predorsal length, mean 50.4% SL (mean 53% or more in A. altior and A. angustifrons ); distance between origins of pelvic and anal fins, mean 20.5% SL (vs mean 19.3 or less); humeral spot rectangular-triangular to oval (P-shaped to indistinct in A. belizianus and A. brevimanus ).

Description

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

Head profile usually straight to slightly concave; snout usually round; lips even, or upper lip slightly protruding; mouth terminal. Pectoral fins usually reach pelvic fin origin; anal and dorsal fins never overlap. Lobes of caudal fin, subequal.

D. 9–11; A. 21–27, modally 25; pect. 10–11. Procurrent unsegmented dorsal rays on caudal fin, variable. Gill rakers on first arch, 20–24, modally 21; on lower limb, 11–14, modally 13. Scales on lateral line, 32–38, modally 35; predorsal scales, 9–14, modally 11; scale rows from lateral line to base of first dorsal-fin ray, 6.5–8, modally 7; to base of pelvic fin, modally 6, up to 7; to base of pectoral fin, 3–5, modally 4; circumpeduncular scales, 14 to mode 16. A single, short scale row on anal-fin base. Nuptial tubercles, simple. Total vertebrae 32–33, 18–19 caudal. Detailed frequencies are given in Table 3.

Largest examined specimen, 94.8 mm SL. Body deep, 36–41% SL. Head rather short, 23–28% SL; orbital diameter, 30–33% HL; interorbital distance, 7.9–10.0% SL, mean 8.8% SL (further morphometric data appear in Table 4).

Anterior fontanel short, straight-sided, blunt-tipped. Supraoccipital process in dorsal view, short, wide-based, slightly concave to angled in lateral view. Vomer rostrally slightly concave. Arms of premaxilla, subequal (dentigerous longer, in population at Mopán); teeth, 0–5. Highest tooth on dentary, first or third; posterior teeth, abruptly smaller. Dorsal edge of longer articular arm, variable. Maxillary, with a convex anteroinferior edge; 1–3 teeth. Metapterygoid, rostral arm longer than ventral, 2 dorsorostral projections. Infraorbital II, triangular with an angled base; infraorbital III, inferoposteriorly semicircular; infraorbital IV, square to rectangular, with a projection; contact between infraorbitals II and III, usually wide. Urohyal rostral end turned up, pointed or blunt; its ventrorostral edge convex, its ventral apex closer to caudal end; ceratohyal foramen oval; rostral vertices of ceratohyal round, the ventral side variable. Epibranchial III, insertion of uncinate process angled, the distal segment of the main body straight. Upper pharyngeal bones, oval to crescent-shaped; lower pharyngeal plate single, its caudal side concave. Dorsal side of hyomandibular, convex. Opercle, sides of dorsal half, parallel; posterior edge, dorsally concave, ventrally straight-convex; ventral tip, sharp. Interopercle, posterior edge, straight-convex. Preopercle, anterodorsal edge, with a median convexity; ventral rim, straight; 2 parallel canals at angle. Four or 5 predorsal bony elements, expanded; rostral edge of first pterygiophore curved or angled. Coracoid with 2–3 interdigitations in suture to cleithrum, a concave caudal edge, a single posteroinferior spine. Caudad process of postcleithrum, globose to digitiform. Proximal edge of pelvic bone, convex. Postanal element, short. Dorsal tip of scaphium, truncate; caudal tip, spiny; dorsoposterior edge, slightly concave. Neural spines under dorsal fin, straight. Sixth to eighth caudal vertebra from tail, with a haemal spine displaced caudad. Rostral edge of largest hypuric plate, variable. Edge of epuric plate on last neural spine, straight.

Humeral spot, rectangular-triangular or oval. Pigment uniformly distributed on anal fin, only edge lighter. Caudal spot, both on peduncle and on fin rays. Live colours were reported for the Belize River population (note in jar UMMZ 167685 by collector C. L. Lundell): ‘dorsal lemon gold, caudal orange over most of each lobe; anal yellowish, becoming bold red forward; pectoral and pelvic red toward outer margin’. The description holds for the populations in Quintana Roo, except that the ‘bold red’ tones are not so evident ( Figure 22 ).

Type material and depositor

Holotype UMMZ 250289 , 94.8 mm SL, southern end of Lake Bacalar , Quintana Roo, Mexico, coll. R. R. Miller, 1974 ( Figure 23 ) . Paratypes: ECOCH 1764 (5 specimens), J .J. Schmitter-Soto and party, 1994, Lake Bacalar at ranch San Carlos, Quintana Roo . ECOCH 1976 (29 specimens), same collectors and year, Laguna Encantada , Quintana Roo . UMMZ 196478 (19), same data as holotype . UMMZ 196540 (75), same collector and year as holotype, ‘pool 2.7 mi [4.3 km] south of Tulum Ruins’ , Quintana Roo . UMMZ 202874 (138), M . Gordon and C. Fairweather, 1949, ‘ 0.5 mi [800 m] E of airport of Belize, lower extension of Gabourel Creek; Belize River dr’ . UMMZ 210875 (142), R . R. Miller, 1982; Río Hondo at La Unión, border Mexico-Belize . UMMZ 246454 (1), J .J. Schmitter-Soto and R. Herrera, 2005, Lake Bacalar at ranch Pantohá, Quintana Roo; UMMZ 246840 (8), P . Chakrabarty and party, 2005, Sittie River , Stann Creek, Belize .

Etymology

Named after the type locality. An adjective.

Distribution

Quintana Roo, Caribbean versant of Yucatan Peninsula, Mexico, south to the Sittie River, Toledo district, Belize, west to Mopán, Guatemala ( Figure 15 ).

Proposed common names

Bacalar tetra, sardinita de Bacalar.

Remarks

The species is a part of clade Ib of Ornelas-García et al. (2008) and corresponds to clade C of Strecker et al. (2004).

There are some clines in meristic traits along the distributional range of A. bacalarensis sp. nov. For example, Mexican populations have 6.5–7.5 scale rows between the lateral line and the dorsal-fin origin, whereas Belizean and Guatemalan populations have 7–8.

Figures

Figure 9. (a) A ceratohyal with rostral vertices angled, foramen drop-shaped (Astyanax angustifrons, UMMZ 196571); (b) with rostral vertices round, foramen oval (A. bacalarensis sp. nov., UMMZ 196540).

Figure 15. Map of northern Central America and southern Mexico, showing distribution localities of Astyanax aeneus, A. altior, A. angustifrons, A. bacalarensis sp. nov., A. caballeroi, A. finitimus, A. macal sp. nov. and A. ocotal sp. nov. A larger symbol denotes the type locality (uncertain for A. angustifrons).

Figure 22. Astyanax bacalarensis sp. nov., live in Lake Bacalar, Quintana Roo, Mexico. © H. Bahena- Basave. Reproduced by permission of H. Bahena-Basave. Permission to reuse must be obtained from the rightsholder.

Figure 23. Astyanax bacalarensis, sp. nov., holotype, UMMZ 250289.