Gobiosoma aceras ( Ginsburg 1939 )

Tornabene, Luke & Van Tassell, James L., 2014, Redescription of the goby genus Gobiosoma (Teleostei: Gobiidae: Gobiosomatini), with the synonymy of the genus Enypnias, Journal of Natural History 48 (23 - 24), pp. 1413-1437 : 1420-1425

Gobiosoma aceras ( Ginsburg 1939)

White-margined goby

( Figures 2 and 3A )

Enypnias aceras Ginsburg, 1939: 61

Type locality

Miraflores Locks, Panama Canal

Material examined

AMNH 233125 , 1 , 32.7 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, J. Van Tassell et al., 7 March 2001 ; AMNH 254723 , 1 , 36.5 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, J. Van Tassell et al., 8 March 2001 ; AMNH 256675 , 1 , 19.6 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, J. Van Tassell et al., 8 March 2001 ; AMNH 256676 , 1 , 36.8 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, J. Van Tassell et al., 7 March 2001 ; AMNH 258323 , 1 , 21.2 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, J. Van Tassell et al., 8 March 2001 ; USNM 407415 , 1 of 5, 22.25 mm SL, El Salvador, C. Baldwin et al., March 2001 ; USNM 407034 , 1 of 2, 13.1 mm SL, El Salvador, Isla Martin Perez , Golfo de Fonseca, C. Baldwin et al., 9 March 2001 ; USNM 408893 , 4 of 5, 13.6–22.55 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, C. Baldwin et al., 7 March 2001 ; USNM 107298 , Holotype, 1, 31.79 mm SL, Panama, Canal Zone : Miraflores Locks, Lower Chamber, Hildebrand, S. F., 26–29 March 1937 ; USNM 123185 , Paratype, 1, 27.38 mm SL, Panama, Canal Zone : Pacific Coast of Panama probably Miraflores Locks, Hildebrand, S. F., 1937 ; USNM 123184 , Paratype, 6 alc and 1 C&S, 24.89– 36.86 mm SL, Panama, Canal Zone : Miraflores Locks, Lower Chamber, Hildebrand, S. F., 26–29 March 1937 ; USNM 81835 , Paratype, 1, 36.18 mm SL, Panama ( Pacific ), Tide Pools, Meek, S.E., Hildebrand, S.F., 22 March 1912 ; USNM 368118 , 1 , 32.68 mm SL, El Salvador, Isla Meanguera , Golfo de Fonseca, C. Baldwin et al., 7 March 2001 .

Diagnosis

A species of Gobiosoma distinguished from congeners by the following characters: prominent barbel adjacent to anterior nare; mental frenum produced into two prominent barbels; second dorsal fin I,13; side of body heavily scaled from caudal peduncle extending to or just falling short of axil of pectoral fin; scales on body ctenoid posteriorly, with ctenii reduced or absent anteriorly; sensory head pores B', C(s), D(s), E, F, H' present; three preopercular pores present; all sensory pores greatly enlarged; body with prominent wide, dark vertical bands on pale background.

Description

Body and head slightly dorsoventrally depressed; body depth at origin of first dorsal fin 19.7–24.7; least depth of caudal peduncle 11.6–14.5; caudal peduncle length 16.9–20.1.

Fins. First dorsal fin VII* (21); dorsal fin spines 1–5 sometimes with short filaments that extend slightly beyond interspinal membrane; second dorsal fin I,13* (16); anal fin I,10* (16); pectoral fin rays 20 (2), 21* (5), 22 (7), 23 (2); pectoral fin length 19.6– 31.4; pelvic fin I,5* (20); pelvic fins completely united by a membrane along their entire length, forming cup-like disc with well-developed, smooth anterior frenum; caudal fin rounded to truncate; segmented caudal fin rays 17* (16), 18 (1); branched caudal fin rays 14 (1), 15* (15), 16 (1); caudal fin length 21.4–27.6.

Scales. Head, nape, abdomen, pre-pelvic area and pectoral fin base without scales; side of body with scales extending from base of caudal fin anteriorly to, or just short of, axis of pectoral fin; scales on side of the body ctenoid, cteni becoming gradually reduced or absent entirely anteriorly; lateral scale rows 32–55 (36 in holotype); transverse scale rows 11–18 (11 in holotype); base of caudal fin typically with four to six scales with reduced cteni; two scales at dorsal and ventral edge of base of caudal fin slightly larger than other basicaudal scales.

Head. Head length 29.7–34.7; post orbital length 17.1–20.4; eye diameter 6.4–7.9; upper-jaw length 9.1–13.3; snout length 5.1–7.8; interorbital width 1.4–3.6; tongue broadly truncate in all but one individual, which was bilobed (possibly due to damage); teeth in upper jaw typically in three rows anteriorly, becoming two rows posteriorly, with inner and outermost rows enlarged and regularly spaced, middle row irregularly spaced and much smaller; outermost row of teeth in upper jaw extending to end of premaxilla or nearly so; teeth in lower jaw arranged in three rows anteriorly, becoming two rows posteriorly; teeth at anterior of lower jaw enlarged and regularly spaced in innermost and outermost rows, middle row irregularly spaced and much smaller; gill opening extends ventrally to just anterior of the pectoral fin base; anterior nare on short stout tube, often with tiny projections or single flap on rim; posterior nare on a tube shorter than anterior nare, lacking flap but sometimes with tiny projections on rim; no barbels on tip of snout; barbel present adjacent to anterior nare, length approximately equal to half to two-thirds the diameter of pupil; lateral edges of mental frenum produced into two prominent barbels, length approximately equal to half to entire diameter of pupil.

Sensory pores and papillae ( Figure 3A ). Head pores B', C(s), D(s), E, F, H' present (pore G present on right side of a single specimen); preopercular pores M', N, O' present; pores on head and preopercle very large and easily visible; six transverse rows of papillae beneath eye; first transverse row beginning beneath anterior margin of eye; last two transverse rows short, beginning at posteroventral corner of eye, just anterior to pore F; longitudinal papillae row b beginning at vertical throw posterior margin of eye; longitudinal papillae row d terminating at transverse row that bisects papillae row b; papillae row n not continuous across nape, but in two separate segments.

Select osteological characters. Vertebrae 27 (11 precaudal + 16 caudal); pterygiophore formula of first dorsal fin 3–221110; first two anal pterygiophores inserted anterior to haemal arch; hypurals 1–2 fused with hypurals 3–4 and terminal vertebral element; one epural; ventral post-cleithra absent; braincase circular in shape; supraoccipital with prominent lateral wings that articulate with sphenotic.

Colour ( Figure 2 ). Background of body and head pale grey; side of body with seven dark vertical bars, approximately equal to eye diameter in width; first vertical bar over nape; bars 2–3 beneath first dorsal fin, with pigmentation of bars extending vertically onto fin; vertical bars 4–5 beneath second dorsal fin, with pigmentation of bars extending vertically onto fin; vertical bar 7 over posterior margin of caudal peduncle and base of caudal fin rays, with pigmentation of bar extending vertically onto dorsal procurrent caudal rays; remaining portion of caudal rays variously pigmented, either with broken dark vertical bars or uniformly dusky; side of face mottled with areas of dark pigment on pale background, with dark areas frequently arranged into two or three vertical or diagonal bars extending from beneath eye; pectoral fin base uniformly dark or mottled; posterior margin of operculum and region between operculum and pectoral fin base frequently with reddish-orange hue; belly and body under pectoral fin base often with yellowish-orange hue; first dorsal fin with two dark blotches roughly positioned over corresponding dark vertical bars on truck, blotches typically separated at least partially by a pale region; second dorsal fin pale at base, uniformly dark across remainder of fin, with pale region at base interrupted by dark blotches that are continuations of vertical bars on truck of body; pectoral fin mottled, distal margin pale.

Habitat

Gobiosoma aceras is known from shallow intertidal areas, including rocky and mangrove tide pools. This species has also been collected from rotenone stations on shallow scuba dives (<12 m) around gorgonian covered boulders and barnacle rubble, and from scree fields that slope down to silty mud.

Distribution

Gobiosoma aceras is known only from the Pacific coast of Central America, from El Salvador to Panama, including in the Canal Zone.

Comparisons

Gobiosoma aceras can be distinguished from its eastern Pacific congeners G.paradoxum , G.hildebrandi and G.chiquita by the presence of barbels near the anterior nare and on the mental frenum. The eastern Pacific G.homochroma also lacks barbels on the mental frenum. Gobiosoma aceras can also be distinguished from all other congeners except G.nudum in having enlarged headpores. Gobiosoma nudum can be easily distinguished from G.aceras by the lack of scales on the side of the body (with the exception of a small patch under the pectoral fin base) versus being heavily scaled, as in G.aceras . The high number of elements in the second dorsal fin of G.aceras (I,13) further distinguish it from all other eastern Pacific Gobiosoma (second dorsal I,12 or less) except G.seminudum . Only G.hildebrandi and G.nudum have vertical banding on the body that is as prominent as the banding in G.aceras . In addition to lacking barbels, G. hildebrandi differs from G.aceras in having fewer lateral scale rows (25–28 versus> 30 in G.aceras ).

Gobiosoma aceras is most closely related to G.seminudum ( Rüber et al. 2003) . The two species were previously considered to belong to a distinct genus Enypnias (also as a subgenus of Garmannia ). Both species are heavily scaled, possess barbels near the anterior nare and on the mental frenum, and have elevated second dorsal counts. Gobiosoma aceras differs from G. seminudum in lacking the supraopercular segment of the sensory canal (pores K', L'), and in having predominately ctenoid scales on the body versus cyloid. There are also prominent barbels on the tip of the snout in G. seminudum that are not present in G.aceras . Overall body pigmentation readily separates the two species as well, as G.aceras has distinct, wide vertical bars that are present in both sexes, whereas male G.seminudum are uniformly dark and females are either mottled or have broken or diagonal bars along the trunk.

Figures

Figure 2. (A)–(D). Gobiosoma aceras. (A)–(C) G. aceras from El Salvador; (D) G. aceras from Panama. Photos by J.L. Van Tassell.

Figure 3. (A, B) Sensory papillae and head pore patterns in Gobiosoma aceras (A), and Gobiosoma seminudum (B). Drawings by J.L. Van Tassell, or modified from unpublished drawings by Isaac Ginsburg.