Coloconger japonicus Machida, 1984

Ho, Hsuan-Ching, Tang, Chi-Ngai & Chu, Tah-Wei, 2021, Coloconger maculatus sp. nov., a species of short-tail eel from eastern Taiwan (Anguilliformes: Colocongridae), Zootaxa 5016 (2), pp. 271-282 : 275-279

Coloconger japonicus Machida, 1984

Figs. 4‒5 ; Tables 1‒2

Coloconger japonicus Machida , in Okamura & Kitajima 1984:87, pl. 52 (type locality: Okinawa Trough, 29°38.9'N, 127°56.0'E, 750‒760 m). Smith 1989:417 (mentioned); Smith 1999:1670 (listed); Shao et al. 2008:239 (checklist); Ho et al. 2015:143 (checklist).

Coloconger raniceps (not of Alcock): Ho et al. 2015:143 (misidentification).

Materials examined. ASIZP 63790, 492 mm TL, R / V Ocean Researcher I,sta. CD193, 22°22'12.0"N, 120°06'36.0"E, Pingtung, southwestern Taiwan, South China Sea, 441 m, 29 Aug. 2002 . ASIZP 64256, 348 mm TL, R / V Ocean Researcher I, sta. CD139, 22°13'12.0"N, 120°20'24.0"E, Pingtung, southwestern Taiwan, South China Sea, 821 m, 23 Nov. 2001 . NMMB-P 34023, 435 mm TL, Dong-sha Island , ca. 20°39'N, 117°05'E, commercial bottom trawl, ca. 500 m, 23 Jan. 2019 .

Description. Based on three specimens collected from Taiwan. Table 1 shows the morphometric data of Taiwanese specimens compared with the type series.

Head length 5.6‒6.2 times in TL; deepest body depth 6.7‒9.3; predorsal 4.5‒5.0; preanal 1.5‒1.6; trunk length 2.1‒2.3; tail length 2.6‒2.9; body depth at pectoral-fin base 8.6‒13.4; body width at pectoral-fin base 15.0‒17.0; body depth at anus 9.8‒12.6; body width at anus 29.0‒36.2.

Snout length 4.2‒5.6 times in HL; eye dimeter 5.2‒6.2; interorbital width 4.2 (n=1); snout-rictus length 3.6‒4.6; lower-jaw length 2.1‒2.3; post-orbital width 1.6‒1.7; gill-opening height 5.3‒6.5; interbranchial width 3.8 (n=1); pectoral-fin length 1.6‒1.8; pectoral-fin base 5.0‒6.3; distance between origins of pectoral and dorsal fins 4.2‒5.6.

Dorsal fin rays 192‒210; anal-fin rays 96‒104; dorsal-fin rays before anal-fin origin 84‒86. Vertebrae: predor- sal 15‒17, precaudal 72‒76; preanal 79‒84, caudal (tail) 68‒74; total 150‒153. Lateral-line pores (tubes): head 4‒6 (n=2); predorsal 9‒10 (n=2); preanal 72 (n=1); total not available (damaged).

Teeth small, each with a flattened tip. Intermaxillary in single transverse row, complete, continuous with maxillary teeth, no teeth on intermaxillary region; no vomerine teeth; single row of small teeth on upper jaw; two complete rows of teeth on lower jaw, those on inner row clearly smaller than outer row.

Head pores open through fleshy tubes, arranged in either regular or irregular series; SO 7 on both side (n=2), first three pores at front of snout, 4 th ‒5 th pores arranged in pair over posterior nostril followed by two pores on interorbital space in ASIZP 64256 and left side of NMMB-P34023, and 4 th pore (e.g. one pore) over posterior nostril on right side followed by three pores on right side of interorbital space in NMMB-P34023; IO 16‒21, first two behind anterior nostril, followed by 5‒9 pores along upper jaw, 4‒6 pores behind rictus and 3‒5 pores behind the eye, many pores arranged in pairs; POM 15‒17, irregularly arranged, 6‒10 along the lower jaw, plus 7‒9 behind rictus; ST 3 (n=2) or 4 (n=1). Additional series of small dermal papillae (or tendrils) behind eye, across supratemporal region, parallel to preopercular canal, neck and at scattered locations elsewhere on head.

Body color uniformly black, except for color lost due to trawling operation; fins darker at base, paler distally.

Remarks. These three specimens were identified as Coloconger japonicus based on the following diagnostic characters: rictus at a vertical through posterior margin of eye; snout longer than eye diameter; a small head, length 16.2‒18.3% TL; eye small, 16.0‒19.2% HL (16.5‒19.0% in types); dorsal-fin origin above anterior half of pectoral fin, distance between origin of pectoral and dorsal fins 32.0‒40.2% pectoral-fin length (31.3‒45.9%); predorsal length 20.1‒22.1% TL (21.4‒21.6%); ST 3 or 4; TV 150‒153 (cf. 149‒153); body uniformly black; sensory pores (tubes) black.

There are several distinct differences between our specimens and the type series. There are 7 pores in two of our specimens (damaged in another one), one with 2 pores over posterior nostril on both sides and one with 1 on right side and 2 on left side. The original description gave 5 SO pores, and likely the pores over posterior nostril were not counted, or the pores do not exist in the type series (based on the original illustration in Machida 1984).

There are 79‒84 PAV and 68‒74 CV in our specimens, while the original description provided 71‒72 "ab- dominal vertebrae" plus 77‒81 vertebrae (149‒153 in total in Machida 1984). According to the literature records, Coloconger species have more PAV than CV reflected by the tail is much shorter than preanal length (tail equal or smaller than trunk length). One possibility is that the author switched the combination of vertebrae (e.g., 77‒81 PAV+71‒72 CV), which seems more reasonable. It is also possible that the author inferred "abdominal" vertebrae as precaudal vertebrae, which we counted as 72‒76 in our specimens. We are not able to verify these differences until the types are examined in detail.

There is no trace of teeth on intermaxillary region in all Taiwanese specimens, whereas the original description reports 4‒6 conical teeth. This difference may attribute to individual or geographic variation.

One specimen (NMMB-P34023) has two pores arranged vertically on the origin of the right side of the lateral line. On the left side, three and two pores arranged vertically which results in 5 (right)/8 (left) HLL, 9/12 PDLL and 76/79 PALL. This may also attribute to individual variation.

One of the specimens examined (ASIZP 63790) was previously identified as C. raniceps ( Ho et al. 2015) and is now reidentified as the present species. It was the only voucher of C. raniceps in Taiwan, and should be removed from the checklist of the marine fishes of Taiwan.

Figures

FIGURE 4. Distribution map of Coloconger maculatus sp. nov. (solid triangle), C. japonicus (open dots), and C. scholesi (solid dot, holotype only).

FIGURE 5. Coloconger japonicus Machida, 1984, ASIZP 64256, 348 mm SL, from Taiwan, preserved condition slightly stained red. Arrows point the dorsal-fin (above) and anal-fin (below) origins. A. Lateral view of left side. B. Lateral view of right side of head.