Uropterygius oligospondylus Chen, Randall, and Loh

Hibino, Yusuke, Kuriiwa, Kaoru, Yamada, Tetsuya, Hatooka, Kiyotaka, Loh, Kar Hoe & Sasaki, Tetsuro, 2020, First Records of Uropterygius oligospondylus (Anguilliformes: Muraenidae) from Minami-iwo-to Island, Southern Japan, Species Diversity 25, pp. 177-182 : 178-181

Uropterygius oligospondylus Chen, Randall, and Loh in Loh et al., 2008

[New Japanese standard name: Kobu-kikai-utsubo] ( Figs 1–3 ; Table 1)

Uropterygius sp. : Sasaki and Horikoshi 2007: 164 (Minamiiwo-to island, Japan).

Uropterygius oligospondylus Chen, Randall, and Loh in Loh et al., 2008: 141 (type locality: Taitung, Taiwan; Taiwan, Solomon and Vanuatu).

Materials examined. KPM-NI 21092, 406 mm TL, KPM- NI 21093, 438 mm TL, southern coast of Minami-iwo-to island, Volcano Islands , southern Japan, 25 June 2007, netbag trap fishing, collected by T . Sasaki; NSMT-P 130223, 506 mm TL, NSMT-P 130224, 351 mm TL, southern coast of Minami-iwo-to island, Volcano Islands , southern Japan, 7 June 2017, hand-net trap fishing, collected by K . Kuriiwa .

Description. Counts and measurements are shown in Table 1. Body moderately long ( Fig. 1 ), laterally compressed, its depth deep; tail not tapered prominently, its length slightly longer or shorter than lengths of head and trunk. Head large, 2.0– 2.5 in trunk and 6.0– 7.2 in TL; dorsal contour of head roughness, snout convex, a distinct broad notch above eye ( Fig. 2 ); snout relatively short, 3.3–4.7 of eye, robust, its anterior tip blunt; anterior nostril extremely short tube, with a prominent but short dermal cover posterodorsally, located slightly posterior to snout tip; posterior nostril narrow oblong slit (pressed tube) with labial flap, located at bottom of notch above mid-eye; eye small, circular, anterior to midjaw; mouth terminal, posterior rictus much behind posterior margin of eye; jaws not recurved, closing completely; lips smooth without cirri; interorbital region narrow; gill opening small, constructed, toward posteroventrally, located below mid-body. Teeth ( Fig. 3 ) relatively long, mostly point- ed, slender, without serration along their edge; teeth of maxilla biserial anteriorly and triserial in posterior part, 4 or 6 teeth on middle row in smaller specimen (NSMT-P 130224, 351 mm TL) and 15 teeth in larger specimen (NSMT-P 130223, 506 mm TL); teeth of dentary biserial anteriorly and triserial in posterior part, 2 or 3 teeth on middle row in smaller specimen (NSMT-P 130224, 351 mm TL) and 9 teeth in larger specimen (NSMT-P 130223, 506 mm TL), teeth on outermost row relatively smaller than that on inner two rows; intermaxillary teeth plate arranged in 3 or 4 irregular transverse rows, teeth on vomer biserial anteriorly and uniserial posteriorly. Sensory pores on head developed, moderate in size, arranged as follows: three supraorbital pores, anterior one ventrally on snout and posterior one above posterior margin of base of anterior-nostril tube; four infraorbital pores along upper lip, first below anterior nostril and fourth distinctly behind posterior end of eye ( Fig. 2 ); six mandible pores; no pores on interorbital, preopercle, and temporal regions; one branchial pore. Fins extremely reduced, low dorsal and anal fins on posterior tip of tail.

Color when fresh. Grey to brownish gray body with black thick reticular pattern, slightly faded ventrally; tip of snout and lower jaw brownish gray; inner mouth with similar pattern of body; margin of eye dark gray; iris yellowish (faded and difficult to see after re-refrigeration).

Color after preservation. Mostly same as fresh condition but becoming dark brown in older specimens (KPM-NI 21092, 21093); eye bluish gray covered with whitish semitransparent membrane.

Distribution and ecological note. The species is distributed in the tropical western central Pacific Ocean from Taiwan (type locality); Solomon Islands; Vanuatu; Minamiiwo-to island of Volcano Islands, southern Japan. In Minami-iwo-to island, it inhabits intertidal zone (0–1 m depth) with many large boulders ( Fig. 4 ).

Remarks. The four specimens were easily regarded as a member of the genus Uropterygius by its shorter trunk than tail length, restricted median fins around tip of tail, subequal mouth closing completely; and eye located above middle of mouth ( McCosker and Smith 1997; Böhlke et al. 1999). Uropterygius oligospondylus was described by Loh et al. (2008) based on three specimens collected from vari- ous localities in the western-central Pacific Ocean. Loh et al. (2008) defined its diagnosis with the following characters: total vertebrae 100–103; body gray with blackish reticular pattern; jaws teeth in three rows; anus close to midbody; head 6.4–7.3, depth at gill opening 12.0–15.5, trunk 2.7–2.8 in TL; eye diameter 21.4–23.3, snout 4.9–6.2 in head length. The present four specimens can be identified as U. oligospondylus because most of these characters are included with the species. Although minor differences can be found in the vertebral counts and proportional features ( Table 1), we consider all of that are intraspecific variations because the species was originally described only three specimens.

Loh et al. (2008) described position of infraorbital pores as “the first just behind anterior nostril, the last below posterior margin of eye”. But the position of the fourth infraorbital pores for all specimens of our study have different condition. So, we have re-checked the infraorbital pores from the holotype and paratypes. The last below posterior margin of eye should have been a mistake recorded in the original description, it should far behind posterior end of eye.

As stated above, Loh et al. (2008) defined the number of rows on jaws of U. oligospondylus is three rows in the diagnosis. However, they wrote “Dentary teeth biserial to triserial” in the original description. In addition, in the present materials, only 4 to 6 teeth on middle row of maxilla and 2 to 3 teeth on middle row of dentary in the smaller specimen (351 mm TL). Therefore, intraspecific and/or ontogenetic difference may be present in the character, so such teeth row character in diagnosis should be modified, future additional smaller specimens may have only biserial on maxilla and dentary. Although Loh et al. (2008) did not mentioned both in the diagnosis and the description, the distinct notch above mid-eye can be characterized for the species. Consequently, we redefine its diagnostic characters as the following characters: total vertebrae 100–103; body gray with blackish reticular pattern; jaws teeth in two or three rows; anus close to mid-body; head 13.7–16.7% TL; trunk 32.8– 36.6% TL; body depth at gill opening 5.8–8.3% TL; eye diameter 3.9–5.3% of head length; snout 16.2–20.3% of head length; and presence of a distinct notch above mid-eye. In those characters, the total vertebral count and the notch above mid-eye are unique for the species.

The two specimens (KPM-NI 21092 and 21093) from Minami-iwo-to island were firstly reported by Sasaki and Horikoshi (2007) as Uropterygius sp. Next year the species was described as a new species but these specimens were not examined. Our research is the first record of U. oligospondylus from Japan, and the northernmost record of the species. In the island, U. oligospondylus inhabits intertidal zone which composed by boulders. All four specimens (NSMT-P 130223–130224 and KPM-NI 21092–21093) were caught by the hand-net/net-bag trap fishing with crushed fish [ Decapterus muroadsi (Temminck and Schlegel, 1844) ]/ bait [ Grapsus tenuicrustatus (Herbst, 1783) ] in the daytime ( Fig. 5 ). Therefore, they may lurk in interstices of boulders, and sniff the smell of the bait. “Kobu-kikai-utsubo” is proposed for the species as a new Japanese standard name referring to its shape of the snout. “Kobu” is Japanese noun for bump.

Comparative material. Uropterygius oligospondylus: TOU-AE 1862 , holotype, 448 mm TL, Taitung, Taiwan; BPBM 16129, paratype, 429 mm TL, Savo, Solomon Islands; USNM 352431, paratype, 535 mm TL, Tanna Island, Vanuatu.

Figures

Fig. 1. Whole specimens of Uropterygius oligospondylus collected from Minami-iwo-to island, Volcano Islands, Japan. a, NSMT-P 130223, 506mm TL; b, NSMT-P 130224, 351mm TL.

Fig. 2. Lateral view of head of Uropterygius oligospondylus, NSMT-P 130223, 506mm TL. Arrows indicate infraorbital pores.

Fig. 3. Mouth of Uropterygius oligospondylus, NSMT-P 130223, 506mm TL. a, upper side; b, lower side.

Fig. 4. Collection site of the present study.

Fig. 5. Collecting situation of the present material. a, net-bag trap fishing; b, hand-net trap fishing.