Trimma xanthum, 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 : 92-95

Trimma xanthum sp. nov.

Yellow-red Pygmygoby Figs. 48 , 52 , Pl. 4 C

Trimma RW sp. 24: Winterbottom et al., 2014:83 (list)

Material. All the type material is from Fiji.

Holotype. ROM 46003, 17.8 mm SL male, drop-off on outer reef edge just SW of Beagle Pass (18°37'06"S, 178°30'21"E), 12– 21 m. 24 Mar. 1983, R Winterbottom et al.

Paratypes. AMS I.18352-035, 2(15.3–20.3), Viti Levu, Suva, Suva Reef (18°08'S, 178°25'E), 10 Jul. 1974. D F Hoese et al. ROM 46004, 7(11.4–20.0), reef-top and drop-off at NW corner of Herald Pass (18°45'19"S, 178°28'19"E), 10– 20 m. 2 Apr. 1983, R Winterbottom et al. ROM 46005, 2(15.2–19.7), drop-off near Herald Pass (18°45'08"S, 178°28'26"E), 25– 30 m. 4 Apr. 1983, R Winterbottom et al. ROM 994CS, 8(10.1–19.5), collected with ROM 46004. ROM 60631, 4(10.5–18.5), collected with the holotype. USNM 236765, 5(10.0–17.7), ocean side just S of Usborne Pass (18°42'S, 178°29'E), 0– 48 m. 14 May, 1982, V G Springer et al. USNM 259739, (18.9), Viti Levu, S. corner Temberua Passage (18°02'S, 178°45'E), 0– 37 m. 30 May, 1982, V G Springer et al.

The following non-type material was also examined: Australian material. Christmas Id: 1 km SE of NW Point: WAM P.26116-002, 3(19.4–21.3), 35– 45 m. Queensland: Ashmore Reef: AMS I.33730-040, 11(11.8–20.8), 32 m; AMS I.33731-094, 13(7.8–20.4), 18 m; AMS I.33717-084, 9(9.9–17.8), 32 m. Herald Cays: WAM P.28537- 0 28, (16.0), 15– 25 m.

Other material. Marshalls: Enewetok: AMS I.30439-001, (18.9), 44 m. Palau: AMS I.17936-006, 5(13–19), 53 m; BPBM 32799, (16.8); ROM 76406, 11(9–15), 18–31 m, ROM 80442, 10(13.6–20.1), 5–18 m; ROM 88102, 4(12.2–20.1), 16– 33 m.

Diagnosis. A species of Trimma with a raised, fleshy, median longitudinal ridge between the eyes and another anterior to the origin of the first dorsal fin; head depth greater than most other Trimma , resulting in a pug-like lateral profile somewhat reminiscent of Gobiodon ; usually 10 dorsal-, 9 anal- and 18–19 pectoral-fin rays; fifth pelvic-fin ray branched once dichotomously and 60–65% length of fourth ray; no scales in the predorsal midline; lateral body scales irregular, and scales above and below any given scale row tending to encroach between adjacent scales of the given row; head orange-red grading through orange to yellow on body when freshly collected, with an oblique yellow bar across the middle of the opercle and another along the vertical limb of the preopercle; pale straw coloured when preserved, often with two horizontally aligned, diffuse dark spots above the dorsal margin of the gill opening.

Description. Based on the holotype and up to 21 paratypes (AMS I.18352–035, ROM 46004, 46005, 60631, 994CS and USNM 236765, 259739). Dorsal fins VI + I 10 –11 (11 once, n = 22), second and third spines longest and reaching to spine of second dorsal fin when adpressed in all but two USNM specimens (where second spine reaches base of second to fourth ray of soft dorsal fin—see Discussion), first ray and anterior element of last ray branched; anal fin I 9 (once 8, once 10), first ray unbranched, anterior element of last ray branched; pectoral fin 18 –19 (once 20, mean = 18.6, n = 22), upper 3 and lower 2–4 rays unbranched (mean = 2.6, n = 7), with 11–14 branched rays in between, fin reaching posteriorly to above urogenital papilla; pelvic fin I 5, first four rays with 2–3 sequential branches, fifth ray branched once dichotomously and 60– 65 % (mean = 62.1, n = 21) length of fourth (reaching to, or almost to, anterior margin of anus), fourth ray reaching posteriorly to between bases of anal spine and third anal-fin ray; no fraenum; basal membrane apparently restricted to about 15–20% length of fourth ray. Scales extremely difficult to count, about 24–25 in lateral series; transverse scales 11–12; cycloid scales on pectoral-fin base, breast, and anterior midline of belly, others ctenoid; scale rows irregular, due to presence of small accessory scales and to tendency for scales in rows above and below any given scale row to extend dorsally and ventrally between adjacent scales in that row; pectoral-fin base with about 7 vertical rows of scales, scales on body apparently not extending anterior to line from upper margin of gill opening and first dorsal-fin origin; 6–7 cycloid scales on breast in midline anterior to pelvic fin. Teeth in inner and outer rows of lower jaw, and outer row of upper jaw of curved, evenly spaced, enlarged canines (inner row half height of outer rows), separated by irregular rows of small, conical teeth. Tongue truncately rounded, about three-quarters pupil-diameter in width. Gill opening extends anteroventrally to below mid-pupil; outer gill rakers on first gill arch 3–4 (once 5) + 15–17 (once 15; mean = 3.8 + 16.2) = 19–22 (mean = 20.1; n = 21). Anterior nares in well-developed tube, posterior opening in short tube; nasal sac raised; nasal apparatus confined to anterior two-thirds of snout. Bony interorbital half-pupil diameter in width, interorbital somewhat concave with raised median ridge of soft tissue (forming a broad, gentle 'W' in cross section); epaxialis reaching anteriorly in dorsal midline to above middle of pupil. Abdominal/caudal vertebral transition Type B.

Colour pattern. Freshly collected. Based on 35 mm colour slide of holotype ( Fig. 52 A). Anterior of head orange-red, becoming somewhat translucent and grading through orange to yellow posteriorly onto body, interspersed with irregular translucent yellow blotches on caudal peduncle; region above posterodorsal attachment of opercular membrane darker red; thin yellow bar along vertical limb of preopercle, another across middle of opercle, and third along posteroventral margin of eye which may then course anteroventrally to distal tip of maxilla; area of cheek underlain by adductor mandibulae muscle light pink; five internal, diffuse, vague dark blotches along vertebral column; dorsal and anal fins hyaline with proximal, half-pupil diameter yellow stripe separated from body by clear area equal in width to stripe, and with melanophores present in distal margins of these fins; caudal fin with scattered yellow spots and blotches; other fins hyaline; iris golden mixed with black pigmentation, inner rim adjacent to pupil a thin red circle. Palau female (19.3, Fig. 52 B) basically similar, but head brick-red, head posterior to eye densely sprinkled with dark brown chromatophores, which decrease in number posterior to insertion of pectoral fin, yellow bands in dorsal and anal fins better defined, as are thin yellow bars on opercle and cheek. Live colouration based on a specimen photographed by K. Martin in Fiji (Pl. 4 C): essentially as above, but head and body with much more red and orange (and less yellow) pigmentation.

Preserved. Plain straw-yellow with head and dorsal half of body sprinkled with fine melanophores and chromatophores, roughly conforming to scale pockets on body; melanophores and chromatophores may be concentrated into one or two diffuse spots each equal to about one-third pupil-diameter above dorsal margin of gill opening; melanophores still visible in distal margins of dorsal and anal fins; a dark median stripe of melanophores in ventral midline between posterior margin of anal fin and procurrent caudal-fin rays.

Etymology. From the Greek ‘xanthos’, meaning yellow, yellowish-red, orange or golden; in allusion to the presence of those colours in freshly collected specimens of the new species. To be treated as a noun in apposition.

Distribution. Collected at Ashmore Reef and Herald Cays on the Great Barrier Reef of Australia, Fiji, Palau, and Enewetok Atoll in the Marshall Islands ( Fig. 48 ). A fairly rarely collected species from depths of 10–53 m, probably more widely distributed in the western Pacific than current records suggest.

Comparisons. The new species belongs to the T. sheppardi species complex, a group which lacks median predorsal scales, possesses a deep head, accessory scales and disjunct scale rows, has a well-developed nasal apparatus occupying two thirds of the snout with the posterior opening in a short tube, and has median fleshy ridges in the interorbital region and on the nape just anterior to the origin of the first dorsal fin. Trimma xanthum differs from T. sheppardi in having 10 (vs. 8–9) dorsal-fin rays; more outer gill rakers on the first gill arch (usually 3–4 + 16–17 vs. 2–3 + 13–15); in lacking the two yellow bars on the cheek beneath the eye and a dark elongate blotch (or two dark spots in a horizontal line) above the origin of the pectoral fin; and in having the anterior portion of the head orange-red rather than pink. It differs from T. yanoi Suzuki & Senou 2008 , and T. haimassum Winterbottom, 2011 in having a single dichotomous branch in the fifth pelvic-fin ray (vs. two) and in having a basal membrane only 20% of the length of the fin (vs. full). It differs further from these species in lacking the extension of the dark areas above the opercular margin anteriorly to the posterior margin of the eye, in the two yellow bars across the opercle and preopercle, and in usually having an oblique yellow stripe from the ventral margin of the eye to the distal tip of the maxilla. Further apparent differences from T. yanoi may be due to different methods of counting scales, although this is difficult to judge. Suzuki & Senou (2008) state that they follow the methods in their previous paper (Suzuki & Senou, 2007). That paper states that, with a few exceptions, they follow the methods of Winterbottom 1996. The methods outlined in the latter paper for counting lateral and transverse scales were employed in this paper. Although the counts for lateral scales given for T. yanoi are comparable to those for T. xanthum (24–26 vs. 24–25), the number of rows of transverse scales is different and non-overlapping (15.5–16 vs. 11–12). Whether the difference is real, or is due to the uncertainty in making these counts due to the irregularity of scale rows, is difficult to assess. At two stations in Palau (AMS I.17936-006 and ROM 88102), these two species were taken in the same collection. Other differences between T. xanthum and T. haimassum include the lack of a stripe from the upper lip posterodorsally across the lower margin of the eye, as well as the absence of the transverse short bands across the dorsal rim of the orbit and dark vermiculations on the snout in the former species.

Three specimens from Palau differed by a minimum of 9% of the CO1 genome from the three other species mentioned above ( Winterbottom et al., 2014).

Discussion. Trimma xanthum appears to be a relatively uncommon species, known from less than 50 specimens, with single lots from the Great Barrier Reef and the Marshalls, 6 lots from Palau and 5 from Fiji. Amongst the Fijian material, one lot (USNM 236765) contains a 14.4 mm SL male in which the second spine of the first dorsal fin is elongated, and reaches the base of the second dorsal-fin ray when adpressed. This lot contains two larger specimens (a 17.7 mm SL male and a 16.9 mm SL female) in which the second dorsal spine is not elongated. Another lot (USNM 259739) contains a single 18.9 mm SL male in which the second spine reaches to the base of the fourth ray when adpressed. Finally, the live specimen photographed (Pl. 4 C) also has a elongated second spine. It seems possible that spine elongation may be associated with some temporal phenomenon (e.g. reproduction), and that elongated spines may be resorbed after breeding. This potential explanation has been suggested for Trimmatom zapotes (Winterbottom, 1989:2409) . The reproductive cycle in T. okinawae is seasonal (from June to September at Kagoshima, Japan), with females spawning every 4–5 days ( Sunobe & Nakazona, 1990). However, there is no information on the longevity of this species. In both T. nasa and T. benjamini , it has been suggested that reproduction continues throughout the year, because the maximum ages recorded for those at species is 3–4.5 months ( Winterbottom & Southcott, 2008; Winterbottom et al., 2011).

In Australia Trimma xanthum is known only from Christmas Island, Ashmore Reef and Herald Cay in the Coral Sea east of the Great Barrier Reef ( Fig. 48 ). The species has been referred to informally as Trimma RW sp. 24 and DFH 21/58.

Figures

FIGURE 48. Distribution map for Trimma taylori (solid pentagon) and T. xanthum (solid circles with white stars). A hollow square with an X in it indicates localities at which both species occur.

FIGURE 52. Trimma xanthum. A: 17.8 mm SL male holotype, ROM 46003, Great Astrolabe Reef, Fiji. B: 19.3 mm SL female, ROM 83072, Tobi Id, Palau. Photos by R. Winterbottom.