Membras pygmaea, Chernoff & Machado-Allison & Escobedo & Freiburger & Henderson & Hennessy & Kohn & Neri & Parikh & Scobell & Silverstone & Young, 2020

Chernoff, Barry, Machado-Allison, Antonio, Escobedo, Jennifer, Freiburger, Michael, Henderson, Elijah, Hennessy, Andrew, Kohn, Grace, Neri, Nola, Parikh, Aashni, Scobell, Sophie, Silverstone, Benjamin & Young, Emily, 2020, Two new miniature silverside fishes of the genus Membras Bonaparte (Atheriniformes, Atherinopsidae) from the Tropical North Atlantic Ocean, Zootaxa 4852 (2), pp. 191-202 : 195-197

Membras pygmaea sp. nov.

Fig. 3A , Table 1

Holotype. FMNH 117282 (40.2 mm SL); Honduras: Depto. Gracias A Dios: Brus Lagoon off the town Brus Lagoon ; R. K. Johnson and G. Glodek, 10 May 1975.

Paratypes. All lots collected with holotype: FMNH 117283 , 240 (23.0– 41.3 mm SL). ANSP 153429 , 5 (27.4– 29.7 mm SL) .

Diagnosis. A species of Membras belonging to the M. martinica species-group, and differentiable from all congeners by the following characters: anus positioned closer to the insertion of pelvic fin than the origin of anal fin and; posterior margins of predorsal and lateral scales smooth or slightly irregular, not laciniate; least depth of caudal peduncle 6.7–8.5% SL; total gill rakers, first arch 16–20, modally 18 or 19.

Description. Morphometric data given in Table 1. A dwarf species, less than 41 mm SL. Individuals ≥ 30 mm SL with large testes or large, apparently ripe eggs. Body elongate in appearance; body tapering posteriorly to slender caudal peduncle. Dorsal fins well separated; spinous dorsal posterior to anus and anterior to origin of anal fin.

Head length <9.4% SL, not truncate posteriorly. Eye positioned within anterior 2/3 of head. Snout bullet shaped, almost pointed anteriorly; lower jaw jutting gracefully outward from prominent joint with quadrate. Dorsal profile of head slightly convex. Mouth terminal, opening just dorsal to horizontal line through midpoint of orbit. Premaxilla curves downward below ventral rim of orbit but not beyond anterior margin. Premaxillary teeth in two rows medially, extending laterally as broad patch of small teeth but not as far as labial ligament. All teeth relatively small, conical and recurved but those of outer row slightly larger. Dentary teeth restricted to small anteromesial tooth patch; tooth patch not extending to labial ligament or where premaxilla crosses dentary in open jaw. Labial ligament with well-developed sheath to end of alveolar process posteriorly; anterior arm thickened, extending to dentary symphysis; bulbular thickening in dorsal portion forming cap to sheath; dorsal arm extending only one-third way up premaxilla. Mesopterygoid teeth present. Vomerine teeth absent.

Spinous dorsal with anterior spines longest; extending posterior to vertical from anal-fin origin. Distal margin of second dorsal fin straight to slightly falcate; posterior rays longest in depressed fin. Anal fin falcate; depressed anterior lobe extending beyond midpoint of fin. Ventral margin of pectoral fin straight to slightly falcate; fin extending beyond vertical line from base of pelvic fin. Posterior margin of extended pelvic fin straight, reaching anterior margin of vent.

Predorsal scales slightly wider than long or of equal dimension; posterior margin smooth or slightly irregular; or with well-developed central knob. Lateral scales grade from much wider than deep anteriorly to shield shaped on caudal peduncle; posterior margin smooth or slightly irregular, never laciniate; anterior margin with well-developed central knob. Circuli restricted to anterior scale field. Radii weak, present only on caudal peduncle scales. Axillary scale of pelvic fin 1/2–1/3 fin length. Interpelvic scale>1/2 length of fin. Modified scales with posterior projections at base of spinous dorsal and along second dorsal fin.

First dorsal fin spines 3(1), 4(10), 5*(18), 6(1). Second dorsal fin rays I,8(4), I,9*(19), I,10(7). Anal fin rays: total I,14(1), I,15(10), I,16*(16), I,17(3); anterior to second dorsal fin 9(1), 10(23), 11*(6). Pectoral fin rays 12(1), 13(20), 14*(7), 15(2). Scales: lateral 41(2), 42(14), 43*(8), 44(5), 45(1); predorsal 19(1), 20(14), 21*(12), 22(3); transverse rows 6*(30); rows around body 14(1), 16*(29); rows around caudal peduncle 12*(30). Gill rakers: total 16(1), 17(3), 18(12), 19*(11), 20(3); upper 3(3), 4*(25), 2(2); lower 13(2), 14(14), 15*(13), 16(1). Vertebrae: total 39(2), 40*(17), 41(8), 42(1); precaudal 15*(24), 16(4); caudal 24(2), 25*(21), 26(5). Vertebral count to origin of: spinous dorsal fin 18(16), 19*(12); second dorsal fin 26(20), 27*(8); anal fin 20(6), 21*(22).

Pigmentation in alcohol. Overall, a lightly pigmented species, most pigment contained on lateral stripe.

Top of head with posterior heart-shaped brain pigment with deeply incised central notch; anterior portion with a few large melanophores; remainder of frontals immaculate. Ethmoid region irregularly pigmented with a few scattered flecks. One or two dark spots under nasal bones. Premaxila with relatively dense pigment dorsally, contrasting with light anterior border, becoming sparser laterally, not extending to labial ligament. Dentary with large scattered flecks, largest under labia ligament, extending to joint with quadrate. Gular region immaculate. Infraorbital series, opercular bones and branchiostegals with small scattered melanophores.

Depth of lateral stripe 1/2–3/4 of orbit, bearing several rows of distinct melanophores, constricted slightly on caudal peduncle. Usually two rows of melanophores between upper edge of lateral stripe and dorsum; scale margins not outlined or crosshatched. Predorsal and interdorsal stripes with one row of melanophores; postdorsal stripe with one or two rows. Body below lateral stripe and breast without pigment. Row of melanophores from posterior margin of anus along sides of anal fin and under caudal peduncle to caudal fin.

Spinous dorsal fin with only a few scattered flecks along spines or immaculate. Second dorsal fin with melanophores along rays, especially proximally, not on membranes; small specimens lacking pigment. Anal fin and pelvic fins immaculate. Pectoral fin with melanophores present only on basal part of rays; fleshy base of fin with at most a few pigment spots, not freckled.

Distribution and Habitat. The species is only known from Brus Lagoon, Depto. Gracias a Dios, Honduras ( Fig. 2 ). The habitat for the collections was a salt marsh with channels bordered by reeds and saw grass. The bottom was peaty. The channel in which the species was collected was on the coastal edge of the lagoon-salt marsh complex.

Etymology. The species-group name, pygmaea , an adjective derived from the Latin meaning little or dwarf, referring to the diminutive size of the species.

Figures

FIGURE 2. Map of Honduras to northern Colombia showing the localities for Membras pygmaea sp. nov., Brus Lagoon, Honduras and M. procera sp. nov., Gulf of Urabá, Colombia.

FIGURE 3. A. Membras pygmaea sp. nov., holotype, FMNH 117282, 40.2 mm SL. B. Membras procera sp. nov., holotype, ANSP 153427, 36.6 mm SL.