Membras procera, 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 : 197-198

Membras procera sp. nov.

Fig. 3B , Table 1

Holotype. ANSP 153427 (36.6 mm SL); Colombia: Gulf of Urabá , 8 17.0’ N, 76 49.5’W; R. V. Pillsbury, 11 July 1966.

Paratypes. All lots collected with holotype. ANSP 153428 (36.1 mm SL); UMML 30095 , 2 (34.0– 36.3 mm SL) .

Diagnosis. A species of Membras belonging to the martinica species-group, distinguishable from all congeners by the following characters: anus between anal fin origin and pelvic fin insertion; tips of pelvic fins reaching anterior margin of vent; posterior margins of predorsal and lateral scales strongly laciniate; lateral scales 42–44; predorsal scales 20–22; length of spinous dorsal fin 8.5–9.5% SL; least depth of caudal peduncle 7.3–8.6% SL.

Description. Morphometric data given in Table 1. Values for holotype indicated by asterisks; number of examined specimens with a given count in parentheses.

A dwarf species, known from specimens less than 40 mm SL, yet specimens with large testes and large eggs. Body slender, elongate with belly curving gracefully to slender, elongate caudal peduncle. Anus almost midway between pelvic fin insertion and anal fin origin. Spinous dorsal fin just anterior to origin of anal fin and posterior to anus. Dorsal fins well separated. Base of second dorsal fin terminates posterior to anal fin.

Head length <25% SL, not truncated posteriorly. Orbit positioned within anterior 2/3 of head. Snout blunt with bullet-shaped lateral profile. Lower jaw angling upwards obliquely from prominent quadrate-angular joint. Dorsal profile of snout curved broadly not pointed; top of head slightly convex. Mouth terminal, opening above midpoint of orbit. Closed lower jaw included within upper jaw. Premaxilla curved downward but not extending below ventral margin of orbit. Teeth in both jaws minute, conical and recurved slightly; largest in premaxilla. Premaxillary teeth generally in two rows, though additional teeth added to series forming wider patch laterally on inner surface of alveolar arm; largest on outer row; teeth extending up to but not beyond labial ligament. Dentary teeth in two uneven rows near symphysis becoming a single row laterally extending up to coronoid process. Labial ligament with well-developed sheath, thickened and extending to distal edge of alveolar process; anterior dentary arm of ligament thickened and extending to symphysis; dorsal arm with base above sheath thickened and bulbous, extending to midpoint of premaxilla. Mesopterygoid teeth present; vomerine teeth absent.

Spinous dorsal elongate and slender, not near base of second dorsal when depressed. Second dorsal fin with falcate posterior margin. Anal fin falcate with pronounced anterior lobe extending beyond midpoint of fin when depressed. Distal margin of pectoral fin straight to slightly falcate extending beyond vertical from base of pelvic fin. Pelvic fin with almost straight distal margin; tip of fin reaching or just extending beyond anterior margin of vent, not covering anus.

Shape of scales varies by region of body. Predorsal scales as wide or slightly wider than long. Lateral scales grade from much wider than long on anterior scales to shield shaped or as long as wide on caudal peduncle scales. Posterior margins of scales notched deeply or laciniate; best developed on predorsal scales. Predorsal scales with one or sometimes two well-developed anterior knobs, remainder of margins irregular, wavy or somewhat laciniate. Lateral scales with a single anterior knob on a straight margin. Circuli restricted to anterior scale field of all scales, posterior field naked. One or two weakly developed radii on caudal peduncle scales only. Axillary scale of pelvic fin triangular, pointed posteriorly reaching from 1/3–1/2 length of fin. Interpelvic scale pointed posteriorly, reaching midpoint of fin. Modified scales with single posterior projection along bases of both dorsal fins.

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

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 blotch of pigment; remainder of frontals almost immaculate. Ethmoid region irregularly pigmented with a few scattered flecks. One or two large melanophores under nasal bones. Premaxila dusky dorsally becoming sparser laterally, not extending to labial ligament. Dentary with a row of dark, large melanophores, largest under labia ligament, extending to joint with quadrate. Gular region immaculate. Infraorbital series, opercular bones and branchiostegals with relatively few scattered pigment specks.

Lateral stripe less than a scale width anteriorly expanding to 1.5 scales at mid-body and decreasing to less than a scale on the caudal peduncle. Lateral stripe with several rows of distinct melanophores, the darkest and largest along the dorsal margin. Usually two rows of melanophores between upper edge of lateral stripe and dorsum; scale margins not outlined or crosshatched. Predorsal and interdorsal stripes with a single file 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 a few large melanophores along anterior spines. Second dorsal and anal fins with melanophores along rays not on membranes. Pelvic fin immaculate. Pectoral fin with melanophores present only on inner surface of basal part of rays; fleshy base of fin lacking pigment spots.

Distribution and Habitat. The species is only known from the Gulf of Urabá in eastern Colombia. It was collected in open water about 1 km offshore. The species was captured at night when lights were submerged below the surface waters to 1 m off the R.V. Pilsbury.

Etymology. The species-group name, procera , an adjective derived from the Latin, meaning long or slender, in reference to the overall shape of this species.

Figures

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.