Enneapterygius olivaceus Dewa, Tashiro, et Motomura, 2023

Dewa, Yuna & Motomura, Hiroyuki, 2024, First records of two triplefins, Enneapterygius rhothion and Enneapterygius olivaceus (Actinopterygii: Blenniiformes: Tripterygiidae), from Australia and Vanuatu, Acta Ichthyologica et Piscatoria 54, pp. 261-268 : 261-268

Enneapterygius olivaceus Dewa, Tashiro, et Motomura, 2023

English name: olive green triplefin Figs 3 , 4 ; Table 2

Material examined.

20 specimens (12.1–22.1 mm SL). AUSTRALIA: AMS I. 22732-008 , male, 22.1 mm SL, Bird Islet , Lizard Island, Queensland, 15°18′00″S, 145°26′59″E, 1981, D. Hoese et al. ; AMS I. 30000-001 , 9 males and 8 females, 12.1–19.4 mm SL, Lizard Island , 15°19′48″S, 145°28′11″E, 1989 . VANUATU: AMS I. 6317 , 1 of 3 specimens, male, 19.7 mm SL, Vila , Efate, 1903, W. A. Haswell leg. ; AMS I. 6451 , 1 of 3 specimens, female, 15.9 mm SL, Vanua Lava , Banks Islands, 1903, W. A. Haswell leg.

Description.

Counts and measurements given in Table 2 . Body moderately elongate, slightly compressed anteriorly, progressively more compressed posteriorly. Dorsal profile of snout straight, moderately steep. Mouth slightly oblique; posterior margin of maxilla reaching to or extending slightly beyond anterior margin of pupil; anterior tip of upper jaw slightly above level of lower margin of orbit (lateral view). Anterior nostril forming membranous tube with short unbranched tentacle, base at level of middle of eye, slightly closer to eye than to upper lip; posterior nostril opening circular, without membranous tube. Eye oriented dorsolaterally; broad leaf-like tentacle on posterodorsal margin, its length longer than nasal tentacle. Interorbital space narrow, its width less than pupil diameter. Opercular margin slightly pointed, reaching to below base of 2 nd or 3 rd spine of first dorsal fin.

Lateral line discontinuous, with anterior series of pored scales and posterior series of notched scales; pored scale series ending below membrane between 9 th and 10 th spines of second dorsal fin; notched scale series beginning below second scale from last pored scale, ending at caudal-fin base; Body scales ctenoid; scales absent on head, including maxilla, interorbital space, preopercle and opercle, and pectoral-fin base, undersurface of head, abdomen and pre-dorsal-fin region; all fin membranes, except basal part of caudal fin, scaleless.

First dorsal fin triangular to trapezoid, its origin vertically above preopercular margin or midway between preopercular and opercular margins; 1 st spine of first dorsal fin longest, thereafter, becoming shorter posteriorly. Origin of second dorsal fin just above 4 th to 6 th pored lateral-line scales, 2 nd or 3 rd spine longest, thereafter, becoming gradually shorter posteriorly, forming rounded distal margin. Third dorsal fin semicircular to trapezoid, its origin just above 19 th and 20 th longitudinal scales, 1 st or 2 nd ray longest, thereafter becoming gradually shorter posteriorly. Anal-fin membranous margin deeply incised between rays; anal fin origin just below 6 th to 8 th spine base of second dorsal fin, its posteriormost tip close to caudal-fin base. Pectoral fin relatively long, its posterior tip pointed and slightly beyond or reaching vertical through base of last spine of second dorsal fin; upper and lowermost pectoral-fin base level with bases of 1 st spine of second dorsal-fin and 3 rd spine of first dorsal fin, respectively. Pelvic fin origin just below vertical through base of 1 st spine of first dorsal fin, its tip not reaching anus. Caudal fin rounded; its length similar to head length.

Nuptial male coloration

(in preservative). Based on Fig. 4 . Body generally yellowish white or brownish. Head, including eye, snout, lips, cheek, and opercle, and pectoral-fin base black or dark brown with melanophores. Pre-pelvic region and undersurface of abdomen black or dark brown with melanophores. Orbital tentacle translucent white, covered by melanophores. Iris greenish white; pupil silver. First dorsal fin black. Second and third dorsal fins generally transparent, with two brown longitudinal bands on fin margin and base, width of former ca. 1 / 2 length of spines, latter somewhat indistinct. Membranous margin of 1 st to 3 rd rays of third dorsal fin transparent, without brownish pigmentation. Pectoral fin transparent, membranes between lower 6–8 rays brownish. Pelvic fin white, its basal part brownish. Anal fin brown, fin margin and base whitish. Caudal fin white with faint brownish bars.

Female coloration

(in preservative). Body generally yellowish white; lateral surface with A- or X-shaped brownish bars. Faint brownish stripes extending from tip of snout to anterior margin of eye, width subequal to upper lip width. Prepelvic region and undersurface of abdomen whitish. Orbital tentacle translucent white, covered by melanophores. Iris navy, pupil silver. Caudal-fin base with vertical brown band. First dorsal fin transparent, with scattered melanophores. Second and third dorsal fins generally transparent, with 2 or 3 irregular oblique brownish bands. Anal fin white. Pectoral fin translucent white; fin rays broadly flecked with brown pigmentation forming ca. 4 or 5 vertical bands. Pelvic fins translucent white. Caudal fin translucent white with narrow brownish vertical bars.

Distribution.

Currently known from Japan (the southern Ryukyu Islands), the Philippines (Talampulan and Negros islands), Australia (Lizard Island), and Vanuatu. ( Dewa et al. 2023; this study) (Fig. 3 ).

Remarks.

The morphological characters of the presently reported South Pacific specimens agreed well with the description of E. olivaceus provided by Dewa et al. (2023), especially as follows: 11–13 (modally 12) second dorsal-fin spines; 18–21 (modally 20) notched lateral-line scales; mandibular pore formula 3 + 1 + 3; head length 28.9 % – 32.3 % (mean 30.6 %) of SL; upper jaw length 9.3 % – 12.0 % (10.6 %) of SL; 1 st spine of first dorsal fin longer than that of 2 nd dorsal-fin, its length 11.0 % – 18.2 % (13.4 %) of SL; orbital tentacle broad, leaf-shaped; head, pectoral-fin base and lower part of pectoral fin brownish in nuptial males; caudal fin whitish in nuptial males; pectoral fin with bands in females; anal fin without distinct bars or lines in both sexes. Although the presently reported specimens had fewer longitudinal series scale rows and scales below the 1 st notched lateral-line scale compared to the type series of E. olivaceus [29–32 (modally 30) and 2 or 3 (3), respectively, in the former vs. 30–32 (31) and 2–3 (2) in the latter], such differences were considered minor and regarded as intraspecific variations.

In Japanese waters, E. olivaceus co-occurs with Enneapterygius minutus in the Ryukyu Islands ( Dewa et al. 2023). Similarly, the two Vanuatu specimens of E. olivaceus examined in this study had been collected with E. minutus specimens (AMS I. 6317, 2 of 3 specimens, 19.4–20.2 mm SL; AMS I. 6451, 2 of 3 specimens, 16.5–16.7 mm SL). Enneapterygius olivaceus is distinguished from E. minutus by the following features: orbital tentacle large and leaf-shaped (vs. slender and pointed in E. minutus ); head long, length 28.4 % – 33.0 % of SL (vs. short, 24.7 % – 32.4 % of SL); upper jaw long, length 9.3 % – 13.1 % of SL (vs. short, 7.4 % – 11.0 % of SL); 1 st spine of first dorsal fin relatively long, length 11.0 % – 18.2 % of SL (vs. short, 7.6 % – 11.4 % of SL); black areas in nuptial males restricted to head and all fins, except for caudal fin [body (except nape and all fins) entirely black in nuptial males]; pectoral fin with faint broad bands in females (with distinct narrow bands in females) ( Dewa et al. 2023; this study).

Enneapterygius olivaceus was originally described based on 28 specimens from the southern Ryukyu Islands, Japan and Talampulan and Negros islands, the Philippines ( Dewa et al. 2023). Accordingly, the presently reported specimens, collected from Australia and Vanuatu, represent the first records of the species from those localities and the Southern Hemisphere.

Figures

Figure 3. Distributional map of Enneapterygius rhothion (red circles) and E. olivaceus (blue triangles). Closed and open symbols indicate localities determined during the presently reported study and previous records, respectively. Black arrows indicate type localities of the two species.

Figure 4. Photographs of preserved specimens of Enneapterygius olivaceus (A: AMS I. 22732-008, male, 22.1 mm SL, Australia; B: AMS I. 6317, male, 19.7 mm SL, Vanuatu; C: AMS I. 30000-001, female, 18.0 mm SL, Australia).