Trimma meristum, Winterbottom, Richard & Hoese, Douglass F., 2015

Winterbottom, Richard & Hoese, Douglass F., 2015, A revision of the Australian species of Trimma (Actinopterygii, Gobiidae), with descriptions of six new species and redescriptions of twenty-three valid species, Zootaxa 3934 (1), pp. 1-102 : 53-55

Trimma meristum sp. nov.

Split-ray Pygmygoby Figs. 27–29

No published names pertain to this species.

Material. Holotype. AMS I.18353–037, 18.3 mm SL male, Fiji, Viti Levu, Suva Harbour, Bird Id, 3 Jul., 1974. B. Russell.

Paratypes. AMS I.18354-104, (19.1), same locality as holotype, 6 m. B. Russell, 9 Jul., 1974. AMS I.20793- 0 90, 2(13.5–19.0), Australia, Queensland, Cape York, NE point of Clack Id (14°03'S, 144°16'E), 3–7 m, 24 Feb., 1979, AMS / AIMS party. USNM 264526, (18.7), Papua New Guinea, Ninigo Ids, just SE of Ami Id (1°14'S, 144°22'E), patch reef, 0–6 m, 22 Oct., 1978, V. Springer et al.

Diagnosis. A species of Trimma with a concave bony interorbital less than half pupil-diameter in width; a slight or no groove posterodorsal to the eye; 8–10 scales in the midline of the predorsal; 7 anal-fin rays; fifth pelvic ray branched twice dichotomously and subequal to the fourth in length, with a full basal membrane; epaxial musculature reaching anteromedially to a point in line with the posterior margin of the pupil in adults; and scale pockets on the head and body strongly outlined by brown chromatophores.

Description. Dorsal fins VI + I 8, second spine longest, reaching to base of spine or first ray of second dorsal fin when adpressed, first ray and anterior element of last ray unbranched; anal fin I 7, first ray and anterior element of last ray unbranched; pectoral fin 17 (once 18), uppermost 3– 4 rays unbranched followed by about 5– 8 branched rays, ventralmost rays unbranched, fin reaching posteriorly to a vertical with bases of anteriormost few elements of anal fin; pelvic fin I 5, first four rays with a single sequential branch, fifth ray branched twice dichotomously and subequal in length to fourth ray, which reaches posteriorly to base of first anal-fin ray, no fraenum, full basal membrane. Lateral scales 23; transverse scales 8; 8 –10 scales in predorsal midline, reaching to above posterior margin of pupil; scales on pectoral base, breast and anterior belly cycloid, other scales ctenoid; four vertical rows of scales on pectoral base, ventralmost smallest and opposite bases of ventralmost 1–3 fin rays, other scales increase in size dorsally; about 4 scale rows anterior to pelvic fin; no scales seen on cheeks or opercles. Teeth in outer and inner rows of both jaws consist of spaced, enlarged, curved canines, those in inner rows about two-thirds height of outer row teeth, two rows separated by 2–3 irregular rows of small conical teeth. Tongue truncately rounded and pupil-diameter in width. Gill opening extending anteroventrally to below anterior half of pupil; outer gill rakers on first gill arch 3 (once 4) + 15 = 18–19. Anterior nares at the end of a short tube, posterior nares a pore with a raised rim, nasal sac somewhat elevated, nasal apparatus confined to anterior half of snout. Interorbital trough moderate, about as broad as deep with steep sides, grading to shallow or absent posterodorsal to eye; bony interorbital width about equal to half-pupil diameter or less; epaxialis reaching anteriorly to a point above posterior margin of the pupil ( Fig. 28 ). Vertebral pattern not recorded, but probably Type B.

Colour pattern. Freshly collected. Not recorded.

Preserved. Brownish with scale pockets on head and anterior body strongly outlined with dark brown chromatophores, fading posteriorly except in Fiji specimens; snout, cheek and dorsal rim of opercle fairly densely and evenly sprinkled with brown chromatophores, ventral portion of opercle and the subopercle without pigmentation; five small (half pupil diameter) saddles across dorsum, first just anterior to base of sixth dorsal spine, second at base of dorsal ray 3, third at base of last ray, and two on the peduncle; pectoral-fin base with evenly distributed brown chromatophores except for a irregularly defined dark bar on the upper two-thirds over the bases of the fin rays, which is made up of densely packed brown chromatophores ( Fig. 29 ).

Etymology. From the Greek ‘meristos’, meaning divided, in allusion to the two dichotomous branches in the fifth pelvic-fin ray resulting in four terminal tips characteristic of the new species.

Distribution. Currently known only from the Great Barrier Reef, the Bismark Archipelago, and Fiji ( Fig. 27 ).

Comparisons. There are two other undescribed species (one described here as T. pentherum sp. nov. and the other currently designated as T. RW sp. 69—see below), and T. cheni Winterbottom 2011 which have outlined scale pockets, a branched fifth pelvic-fin ray, and at least some branched pectoral-fin rays. Trimma meristum differs from all three of these species in having only seven anal-fin rays (vs. 8–10) and in the fifth pelvic-fin ray being branched twice and subequal to fourth (vs. branched once and 50–60% length of fourth). It differs further from the currently undescribed Trimma RW sp. 69 ( Indonesia, Philippines, Papua New Guinea, Solomons, Vanuatu and Fiji) in having one less dorsal-fin ray (8 vs. 9), second spine not elongated (vs. elongated), a scaleless opercle (vs. 2–3 cycloid scales on opercle), and a uniformly pigmented cheek (vs. cheek with two light bars). Trimma meristum differs further from the other undescribed species and from T. cheni in having 17 (vs. 18–19) pectoral-fin rays, and in having the epaxialis reaching anteriorly to a vertical above the posterior margin of the pupil (vs. posterior margin of the eye). An additional difference from Trimma cheni ( Indonesia, Philippines, Papua New Guinea) is the hyaline dorsal fin (vs. a dark basal stripe), and from the undescribed T. RW sp. 54 (Line Islands, Micronesia, Marianas, Papua New Guinea) in the short second dorsal spine (vs. elongated) and the absence of the trough posterodorsal to the eye (vs. present). Trimma meristum differs from T. pentherum sp. nov. in the double branched fifth pelvic-fin ray (vs. branched once), branched pectoral-fin rays (vs. unbranched) with four vertical rows of scales on its base (vs. three rows), one more outer gill raker on the lower limb of the first arch (15 vs. 12–14), anterior extent of epaxialis (to posterior pupil vs. posterior eye), and in the less well defined and incomplete vertical bar on the pectoral-fin base (vs. well defined and complete).

Discussion. This appears to be a rare species (five known specimens), because it seems to occur in the relatively well-collected shallow waters of corals reefs. The species is normally found on shallow turbid reefs in depths of less than 10 m. In Australia it is known only from reefs close to the shore.

It has informally been referred to as Trimma DFH sp. 48 or Trimma RW sp. 72.

Figures

FIGURE 27. Map of the distribution of Trimma maiandros (solid diamonds) and T. meristum (solid square with white center). A solid circle with a white star indicates localities at which both species occur.

FIGURE 28. Trimma meristum, 19.0 mm SL male, AMS I. 20793 - 090, dorsal view of head, stained with cyanine blue. Photo and image enhancement by R. Winterbottom.

FIGURE 29. Trimma meristum, 19.0 mm SL male (preserved), AMS I. 20793 - 090, Cape York, Queensland. Photo by R. Winterbottom.