Yirrkala nkust sp. nov.

Figs 1, 2, 3 A, Table 1

Materials examined.

Holotype • NMMB-P 38652, 496 mm TL, ca 23°40'N, 119°36.6'E, Chi-kan, Bai-sha, northern Penghu, western Taiwan, Taiwan Strait, ca 30–50 m depth, 12 July 2021. Paratypes • NMMB-P 38645, 315 mm TL, 12 July 2021; NMMB-P 39317, 462 mm TL, 16 August 2022; KMNH VR 100650, 297 mm TL, 23 July 2024; all collected from near the type locality.

Body depths in parentheses are possibly the maximum depth. a from Bleeker (1858); b from Norman (1939); c from McCosker (2022); and d estimated from Norman (1939).

Diagnosis.

An elongate species of Yirrkala with the following combination of characters: body reddish brown without speckles, snout paler; supraorbital pores (SO) 1 + 3; dorsal-fin origin just above gill opening; lateral-line pores before anus 72–78; predorsal vertebrae 7–8, preanal 72–75, and total 147–152; MVF 8-73 - 150.

Description.

Body elongate, subcylindrical, tip of tail laterally compressed and extremely pointed (Figs 1 A, 2 A). Head moderate in size, 15.7–17.0 in TL (17.0 in holotype); preanal length mostly equal to tail, 0.9–1.1 in tail length and 1.9–2.1 in TL (0.9 and 1.9 in holotype).

Snout relatively longer, 3.4–3.7 times eye diameter (3.7 in holotype), its tip pointed; distinct median groove ventrally on snout, its anterior tip reaching to midpoint of anterior-nostril-tube base; slope of dorsal surface of snout smooth, without notch or distinct hump. Anterior nostril tubular, short, tube length about equal to pupil diameter; posterior nostril oval in shape with an inner valve, located on anteroventral margin of eye, opening ventrally, covered by a flap extending slightly below edge of mouth gape. Eye small, covered by a transparent skin; center of eye anterior to mid-jaw (Figs 1 B, 2 B). Interorbital region wide, weakly convex (Figs 1 C, 2 C). Mouth inferior, distance from tip of snout to anterior tip of lower jaw 3.0–3.3 times eye diameter (3.3 in holotype); lower jaw short, its tip relatively pointed, not reaching anterior-nostril tube (Figs 1 B, 2 B, D); rictus short, posterior end of gape slightly behind a vertical through posterior margin of eye; lips smooth with a fold along upper lip, extending from second infraorbital pore to postorbital pore or rictus. Gill openings positioned ventrolaterally of breast, relatively close each side; shape of opening slightly curved, diameter more than twice eye diameter.

Sensory pores on head developed, arrangement of those pores as follows (Fig. 3 A): 1 (ethmoid) + 3 on supraorbital, 3 + 3 on infraorbital, 4 on lower jaw, 2 on preopercle, and 5 on supratemporal, one of those on mid-temporal; a single median interorbital pore.

Lateral-line pores small but obvious. Lateral line almost complete except for near tip of tail, nine anterior to a vertical through gill opening, seven or eight (eight in holotype) anterior to dorsal-fin origin, 72–78 (77) anterior to mid anus, and total 149–152 (151).

Teeth pointed, slightly recurved posteriorly; 12–15 teeth on maxilla and 12–13 dentary uniserial; 10–12 vomerine teeth biserial anteriorly and uniserial posteriorly; intermaxillary with four teeth arranged in two rows.

Median fins low but obvious; origin of dorsal fin slightly behind a vertical through anterior edge of gill opening but not behind posterior edge, ending anterior to tip of tail about 1 eye diameter; origin of anal fin slightly behind anus, ending same as dorsal fin; caudal and pectoral fins absent.

Coloration. Just after captured (Fig. 1), body greenish brown anteriorly, reddish brown posteriorly; lateral-line pore not margined; head generally greenish brown, postorbital region pinkish; snout with extremely pale brown transverse band dorsally in holotype, paratype also paler but tip of snout not darker; fins similar color of body. After preservation, body color faded, changed to brown to pale brown, trunk weakly bicolored, melanophores remaining dorsally.

Etymology.

The scientific name nkust is the acronym of the National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan, which supports our research work. Used as a noun.

Distribution.

Known from the northern regions of Penghu Islands, an archipelago in the Taiwan Strait off western Taiwan. The type series was collected from bycatches of the Silver-stripe round herring (Spratelloides gracilis) at depths about 30– 50 m.

Remarks.

The position of the dorsal-fin origin compared to that of gill opening is an important character for diagnosing Yirrkala species. Based on the morphological information of several species (i. e. Yirrkala ori McCosker, 2011 and Y. misolensis), the origin of dorsal fin quite consistent, showing less intraspecific variation.

The new species has the dorsal-fin origin situated above gill opening (verticals between anterior and posterior edges of the opening). The character is shared by Y. ori only, as other 13 species, including Y. chaselingi, Y. lumbricoides, Yirrkala moorei McCosker, 2006, Yirrkala tenuis (Günther, 1870) before; Yirrkala calyptra McCosker, 2011, Y. gjellerupi, Yirrkala insolitus McCosker, 1999, Y. kaupii, Yirrkala macrodon (Bleeker, 1863), Yirrkala maculata (Klausewitz, 1964), Y. misolensis, Yirrkala omanensis (Norman, 1939), Yirrkala philippinensis (Herre, 1936), have their fin origins clearly behind the gill opening (Bleeker 1863; Whitley 1940; McCosker 1999, 2006; McCosker et al. 2007; McCosker 2011; Chiu et al. 2022; this study).

Yirrkala nkust sp. nov. differs from Y. ori in having 1 + 3 supraorbital pores (vs 1 + 4), and the position of the lower-jaw tip (not reaching base of the anterior-nostril tube vs beyond posterior edge of the base). The new species has similar vertebral counts of Y. lumbricoides but not overlapped in the count of the predorsal vertebrae (7 or 8 vs 5 in Y. lumbricoides), and the total vertebrae (147–152 vs 150–159) is available (McCosker 2022; this study).

In addition, although Muraena fusca Zuiwe, 1793 was regarded as a valid species of Yirrkala by Fricke et al. (2018), this name should be treated as a nomen dubium. Its original description is insufficient which lacks direct evidence to identify it to any ophichthid and whereabouts of its holotype is unknown. Sphagebranchus brevirostris Peters, 1855, which has been regarded as conspecific with M. fusca (Fricke et al. 2018), should be treated in a future work.