Bathyuroconger albus Smith & Ho & Tashiro 2018, sp. nov.

Bathyuroconger albus sp. nov.

English name: White large-toothed conger

Figs. 2, 3, 4, 5A; Tables 1, 2

Bathyuroconger vicinuS (not of Vaillant, 1888): Shao et al., 2008:239 (in part). Smith, 1999:1686 (in part). Ho et al., 2015:146 (in part).

Holotype. USNM 400323 (1, 432), Daxi, Yilan, northeastern Taiwan, bottom trawl, 4 May 2010.

Paratypes. Collected from Daxi, Yilan, northeastern Taiwan. ASIZP 60162 (6, 190+‒429), 650 m, 15 Sep. 1997. ASIZP 60175 (1, 294), 30 Nov. 1997. ASIZP 61124 (2, 177+‒206), 500 m, 7 Dec. 2000. ASIZP 61475 (1, 302), 400 m, 13 Jul. 2000. ASIZP 63134 (8, 360‒585+), 24.81‒24.82° N, 122.07‒122.18° E, 350‒650 m, 24 Apr. 2004. ASIZP 63251 (1, 337), 21 Mar. 2004. BSKU 50487 (1, 492), 23 Apr. 2012. NMMB-P11157 (1, 625), NMMB-P11158 (2, 380‒430), 8 Dec. 2010. NMMB-P22058 (10, 320‒480), 1 De. 2014. NMMB-P 26391 (3, 487‒615), 28 Jun. 2017. USNM 400322 (1, 493+), 4 May 2010. USNM 400324 (1, 416+), 4 May 2010. USNM 400325 (6, 193+‒375), 4 May 2010. Collected from Suao, Yilan: CAS 216686 (1, 295+), 24 Jul. 2001. Collected from Dong-gang, Pingtung, southwestern Taiwan, South China Sea: NMMB-P26613 (1, 475+), NMMB-P26614 (1, 713), NMMB-P26615 (2, 600+‒658), NMMB-P26616 (1, 468), 23 Jul. 2017; USNM 437346 (1, 520+), 22 May 2014.

Non-types. ASIZP 63293 (4, 398+‒615+), 24.81‒24.82°N, 122.07‒ 122.18°E, off Daxi, Yilan, NE Taiwan, 24 Apr. 2004. USNM 377318 (1, 315+), 24.83°N, 122.00°E, Daxi, Yilan, NE Taiwan, 300‒600 m, 27 Mar. 2004. ASIZP 66175 (1, 290), CD321, South China Sea, 954 m, 19 Aug. 2005. NMMB-P1799 (1, 410), Daxi, NT Taiwan, 9 Sep. 2003. NMMB-P11152 (1, 271), Daxi, NE Taiwan, 5 Jun. 2010. NMMB-P21654 (1, 230), Dong-gang, SW Taiwan, 27 Aug. 2008.

Diagnosis. Bathyuroconger albus is distinguished from the other species by its pale coloration, light grayishbrown dorsally and lighter ventrally, head with pigmentation under skin and covered by semi-transparent unpigmented skin; a moderately reduced gill opening separated from pectoral-fin base by a distance less than diameter of gill opening; and 168‒177 vertebrae.

Description. Measurements in %TL: PAL 35.8‒41.8, PDL 13.8‒16.2, HL 10.9‒12.6, TR 24.8‒30.9, DA 4.0‒7.0. In % PAL: PDL 33.5‒43.3, HL 25.6‒33.7, TR 66.3‒74.4, DA 10.0‒19.2. In % HL: S 21.6‒26.0, E 9.7‒15.7, IOW 15.0‒23.2, UJ 30.7‒42.3, GO 5.1‒18.6, IB 19.6‒42.7, PL 29.4‒49.0. Pores: PALL 42‒48, PDLL 7‒11, PPLL 4‒6, SO 3, IO 5, POM 10 (rarely 9), ST 1. Vertebrae: PDV 10‒14, PAV 45‒54, PCV 53‒58, TV 168‒177.

Body slender, cylindrical anteriorly, gradually tapering and compressed posteriorly, tail thin, anus anterior to mid-body at slightly more than one-third total length. Dorsal and anal fins confluent with caudal fin; dorsal fin begins above posterior half of pectoral fin; anal fin begins immediately behind anus. Head stout, rounded, deeper than body; jaws nearly equal. Snout short and blunt, rounded in dorsal view, about 1.1‒2.6 times eye diameter. Eye moderate, over posterior third of upper jaw, posterior margin at level of rictus; interorbital space relatively broad, its width greater than eye diameter. Anterior nostril short and tubular, at front of snout; posterior nostril in front of mid-eye, a simple pore. Gill opening moderately small, separated from pectoral-fin base by a distance less than diameter of gill opening, its upper end at level of lower pectoral-fin base.

Head pores moderately enlarged, not elongate and slit-like. Supraorbital pores 3; first pore small, at tip of snout on edge of upper lip; second pore larger, above and behind first, at level of and anterior to anterior nostril; third pore slightly larger and above anterior nostril; no pores on interorbital space. Infraorbital pores 5; first immediately behind anterior nostril; second below and behind first, on edge of lip between anterior and posterior nostrils; third below anterior margin of eye; fourth below posterior part of eye; fifth behind rictus. Preoperculomandibular pores 10 (rarely 9); 7 (rarely 6) on mandibular section and 3 on preopercular, the last one at about level of first lateral-line pore. A single supratemporal pore with tube-like rim, anterior to level of first lateral-line pore. Lateral line complete, lateral-line pores large; predorsal 7‒11 (mean 9); prepectoral 4‒6 (mean 5); preanal 42‒48 (mean 45).

Vertebrae: predorsal 10‒14; preanal 45‒54; precaudal 53‒58; total 168‒177, MVF 13‒49‒173. ASIZP 66175 has 8 predorsal vertebrae and ASIZP 63293 (1 of 4, 398+ mm) has 6 predorsal vertebrae, both are clearly fewer than other specimens.

Teeth large and pointed, generally smaller than those of the B. vicinus group. Intermaxillary teeth in two transverse rows, each with 4‒6 enlarged fang-like teeth, exposed when mouth closed. Vomer with 2 large median teeth and 2‒8 small teeth beside and/or behind. Maxilla with 3 irregular rows of teeth on anterior portion, becoming 2 rows posteriorly, those in outermost row larger and scattered in arrangement. Dentary with 4 irregular rows of enlarged teeth on anterior portion, those on outer 2 rows fang-like and exposed when mouth fully closed, gradually narrowing to 2 rows posteriorly, those of outermost row larger.

Coloration. Pale grayish-brown in preservative, somewhat darker dorsally; head with pigmentation under skin and covered by semi-transparent unpigmented skin; dorsal half of anterior two-thirds and posterior one-third of body grayish brown; ventral half of anterior two-thirds of body whitish or only covered by scattered pigmentation; irregular but clear boundary between pigmented and unpigmented areas. Pectoral fin transparent; dorsal and anal fin white in anterior portion, some with internal pigmentation on rays, gradually becoming pale basally and with broad black margin posteriorly; caudal fin black. Oral cavity and tongue grayish; gill chamber grayish, gill cover region grayish from outside view. Peritoneum blackish, gut and stomach black.

Distribution. This species is currently known only from Taiwan, where it seems to be the most common species of Bathyuroconger. Specimens were collected at depths of ca. 300‒ 954 m.

Ecological note. All specimens were collected by bottom trawl together with many demersal fishes, which may indicate this species lives near the bottom. Smith (1989a) commented that the enlarged sensory pores and the soft body may suggest that this species lives associated with the bottom but is more or less pelagic.

Etymology. From the Latin albus, white, in reference to its pale coloration compared to other congeners.

Remarks. Bathyuroconger albus sp. nov. has been confused with B. vicinus, a species described from the Atlantic and reported to occur worldwide. It differs primarily in the coloration and the size and position of the gill opening. Bathyuroconger albus is lightly pigmented dorsally and pale ventrally, whereas B. vicinus is brownish to blackish. In B. albus, the gill opening is smaller and separated from the pectoral-fin base; in B. vicinus the gill opening is larger and in contact with the pectoral-fin base. It has 168‒177 total vertebrae, whereas the various B. vicinus populations have 180‒186; it also has 53‒58 precaudal vertebrae vs. 57‒66 in B. vicinus. Although overlapping, the snout length, eye diameter, upper-jaw length and gill opening relative to head length are smaller in B. albus than B. vicinus. Moreover, the fang-like teeth in the jaws are generally smaller in B. albus than in B. vicinus.

It differs from B. hawaiiensis in the paler color (dark brown in B. hawaiiensis) and fewer vertebrae (168‒177 vs 201‒210).

Bathyuroconger albus is similar to B. dolichosomus sp. nov. described below in the coloration and gill opening, but it is clearly distinguished by the shorter trunk (2.0‒2.9 vs 3.2 times in head length), fewer preanal lateral-line pores (42‒48 vs 61), and fewer preanal vertebrae (45‒54 vs 63).

TABLE]. Morphometric anđ meristic đata of three Bathyuroconger species anđ comparative đata of B. vicinus. HT =Holotype.

Bathyuroconger albus differs from B. parvibranchialis and B. fowleri in the coloration (light gray vs brown) and larger gill opening (very small in B. parvibranchialis and B. fowleri and separated from the pectoral-fin base by a distance greater than the diameter of the gill opening). It further differs from B. parvibranchialis in the more posterior dorsal-fin origin (over middle of pectoral fin vs over base of pectoral fin), more predorsal vertebrae (10‒14 vs 7‒10), more preanal vertebrae (45‒54 vs 43‒48), and fewer total vertebrae (168‒177 vs 181‒189). It also has a greater preanal length (35.8‒41.8 %TL vs 33.3‒37.1) and predorsal length (13.8‒16.2 %TL vs 12.6‒14.5)

Although only six specimens were collected from southwestern Taiwan (South China Sea), some differences are found compared to those specimens collected from northeastern Taiwan (NW Pacific Ocean). The preanal length and trunk length in percentage of total length are slightly larger in the former than the latter. The head length in percentage of preanal length is slightly smaller in the former than the latter. The meristic data show no difference between populations.