Trimma pentherum, 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 : 70-73

Trimma pentherum sp. nov.

Mourning Pygmygoby Figs. 39–40

No published names pertain to this species.

Material. Holotype. USNM 243051, 20.3 mm SL male, Fiji, Lau Group, Matuku Id, S side outside channel entrance (19°09'38"S, 179°45'23"E), 20– 23 m. V.G. Springer et al., 24 Apr., 1982.

Paratypes. ROM 60186, 4(14.6–19.5), collected with holotype. USNM 236743, (19.7), Fiji, Ono–Ilau, outer barrier reef on NW side (21°38'S, 178°45'W), 14– 15 m. V.G. Springer et al., 1 May, 1982. USNM 236755, 2(16.7–20.2), Fiji, Lau Group, Matuku Id, S side outside channel entrance, 23 m. V.G. Springer et al., 25 Apr., 1982. USNM 243046, 5(12.6–19.1), locality as for holotype, 0– 12 m. V.G. Springer et al., 24 Apr., 1982.

Non-types. Australian Material. Queensland: Ashmore Reef: AMS I.33738-072, (13.8), 4– 24 m. FNQ Party; (10° 13.16S, 144°24.89’E), AMS I.33731-087, (17.2), 1– 18 m. Boot Reef: AMS I.33747-032, 5 (13–16), 23– 30m. Herald Cays: WAM P.28537-003, 2(14–15), 15– 25 m. Holmes Reef: WAM P.28541-045, 3(17–18), 2–14 m; WAM P.28538-016, 2(16.9–17.3), 15– 18 m. Osprey Reef: AMS I.25112-031, 4(9–20), 1– 15 m. AMS I.25112- 0 34, 3(16–18), 1–15 m; BPBM 31754, (18.2).

Other material. Palau: Helen Reef: ROM 83246, 3(11–16), 18–26 m; ROM 83252, 4(11–15), 4–25 m; ROM 83330, 2(13–17), 10–30 m; ROM 83349, (18), 7–33 m; ROM 1803CS, 2(15–18), 10– 30 m. Vanuatu: Banks Group, Mota Lava Id, AMS I.37924-027, (13.2), 1– 10 m. Emae, AMS I.17475-053, (20), (17°02'S, 168°17'E), 25 m.

Diagnosis. A species of Trimma with a concave bony interorbital less than half pupil-diameter in width; a slight or no groove posterodorsal to eye; scales in the midline of the predorsal region; no opercular scales; fifth pelvic ray branched once dichotomously and more than 80% the length of the fourth ray; epaxial musculature reaching anteromedially to a point in line with the posterior margin of the eye in adults; no elongated spines in first dorsal fin (second spine longest, reaching to the region of the base of the second dorsal-fin spine); scale pockets strongly outlined by melanophores and chromatophores; a dark, vertical bar on the base of the pectoral fin; and six grey saddles across the dorsum.

Description. The description is based on 13 specimens, 6 male, 6 female, 1 unsexed, from Fiji. Dorsal fins VI + I 8, second spine longest, reaching to base of spine of second dorsal fin or little beyond when adpressed, first ray and anterior element of last ray unbranched; anal fin I 8, first ray and anterior element of last ray unbranched; pectoral fin 18–21 (holotype 21L/20R; mean = 19.7), all rays unbranched, fin reaching posteriorly to point in line with vertical from region between anus and base of second anal-fin ray; pelvic fin I 5, first four rays with a single sequential branch, fifth ray branched once dichotomously and 80–90% of fourth, which reaches posteriorly to base of anal spine, no fraenum, full basal membrane (usually torn). Lateral scales 23 (once 24); transverse scales 7; predorsal scales 7 –8 (mean = 7.2, n = 11); scales on pectoral base, breast, and anterior belly cycloid; other scales ctenoid; three vertical rows of scales on pectoral base, ventralmost smallest and opposite bases of ventralmost 1–3 fin rays; no scales seen on cheek or opercles. Teeth in inner and outer rows of lower jaw, outer row of upper jaw and few teeth in inner row near symphysis consist of curved, spaced, enlarged canines; several irregular rows of small, conical teeth between these. Tongue truncately rounded, sometimes with central point at tip, about twothirds pupil diameter in width. Gill opening to beneath mid-pupil or slightly anterior to this; outer gill rakers on first gill arch 2–4 + 12–14 = 14–18 (holotype 3 + 13; mean = 3.0 + 13.0). Anterior nares short tube, posterior porelike with raised rim, nasal sac slightly elevated, rather small, and confined to posterior two-thirds of anterior half of snout. Interorbital trough moderate, as broad as deep, grading to shallow or absent posterodorsal to eye; width of bony interorbital about equal to half-pupil diameter; epaxialis reaching anteromedially to point in line with posterior margin of eye. Vertebral pattern Type B, although in larger of two specimens examined for this character (ROM 1803CS) first caudal vertebra had only a single large haemal arch (two arches, in a typical Type B configuration, present in smaller specimen).

Colour pattern. Freshly collected. From a colour slide of a specimen from Holmes Reef (image quality not sufficient for reproduction). Dull yellow anteriorly grading to bright yellow on caudal peduncle and fin; scale pockets strongly outlined with melanophores and chromatophores; dark bar on pectoral-fin base adjacent to fin-ray bases; six grey saddles across dorsum, first on nape, thinning ventrally as it continues across pectoral-fin base just anterior to dark bar, second at bases of third to fifth spines of first dorsal fin, third at base of spine of second dorsal fin, fourth at base of last dorsal-fin ray, fifth at mid-peduncle (second to fifth about pupil-diameter in size); sixth just anterior to procurrent caudal-fin rays and about one-third pupil-diameter in size; head anterior to vertical limb of preopercle uniform grey-brown; iris red with yellow mottling; first dorsal with vague dark basal stripe; scattered chromatophores in dorsal, caudal, anal and pelvic fins; pectorals hyaline. Specimens from Vanuatu and Solomons generally similar. Six specimens (11.7–18.2 mm SL) from Helen Reef, South West Islands of Palau were photographed (see Fig. 39 ). They differ in having smaller grey saddles, and anteriormost saddle does not connect to diffuse white bar margining anterior edge of black pectoral bar, quarter pupil diameter basal black stripe in dorsal fins, margined distally by similar width or slightly wider yellow stripe with remainder of fins more or less translucent, anal fin width proximal and distal diffuse black stripes with area in between yellow, caudal fin mostly yellow with more translucent outer margins, and pelvic fins transfused with yellow. Snout, cheek and opercle heavily suffused with large brownish chromatophores (opercles appear suffused with reddish orange, presumably from underlying gill filaments) with lighter diffuse yellowish bars on posterior margin of cheek just anterior to vertical limb of preopercle, and another from anteroventral eye to posterior tip of maxilla.

Preserved. Similar, but reds and yellows not apparent.

Etymology. From the Greek “pentheros”, of mourning, in a perhaps far-fetched allusion to the black bar on the pectoral-fin base which, with considerable imagination, could be viewed as analogous to the black arm band worn in certain cultures to signify the death of a close friend or relative.

Distribution. This species has been collected from Tonga to the Great Barrier Reef and north to the South West Islands of Palau ( Fig. 40 ).

Comparisons. Among the species in the genus with outlined scale pockets, a branched fifth pelvic-fin ray and unbranched pectoral-fin rays, T. pentherum is very similar to T. emeryi . It differs from that species in possessing the dark bar on the pectoral-fin base, the 6 grey saddles over the dorsum, the yellow rather than brown background colouration, and, modally, in pectoral-fin ray number (19.7 vs. 17.5). It differs further from T. flavicaudatum in the longer fifth pelvic-fin (90% vs. 75% fourth ray) and in having a uniformly coloured cheek and snout (irregular light—red in life—spots and areas in T. flavicaudatum ), but shares with that species the bright yellow posterior region of the body. Trimma pentherum differs from an undescribed species from the Pacific plate in one fewer dorsal- and anal-fin ray (8 vs. 9) and in the dark pectoral bar and grey dorsal saddles.

Discussion. Further material is necessary to explore the possibly significant variation in pectoral-fin ray number between the Australian (18–19, mean = 18.8, n = 4), Palauan (18–19, mean = 18.4, n = 12) and Fijian (19–21, mean = 20.0, n = 11) populations.

The species is known from depths of around 10– 30 m. In Australia it is known only from islands of the Coral Sea east of the Great Barrier Reef. Trimma pentherum appears to be a relatively rare species with a limited distribution. It has been referred to informally as Trimma DFH sp. 5 or Trimma RW sp. 35.

Figures

FIGURE 39. Trimma pentherum, 15.2 mm SL male, ROM 83252, Helen Reef, Palau. Photo by R. Winterbottom.

FIGURE 40. Distribution map for Trimma pentherum (open triangles) and T. preclarum (solid squares). A solid star indicates localities at which both species occur.