Bathyuroconger fowleri, Smith & Ho & Tashiro, 2018

Smith, David G., Ho, Hsuan-Ching & Tashiro, Fumihito, 2018, Eels of the genus Bathyuroconger in the northwestern Pacific, with descriptions of four new species (Anguilliformes: Congridae), Zootaxa 4454 (1), pp. 147-167 : 158-160

Bathyuroconger fowleri sp. nov.

English name: Fowler’s large-toothed conger

Figs. 4 , 7 , 8A ; Tables 1, 2

SilveSterina parvibranchialiS (non Fowler, 1934): Fowler, 1934:275 (part).

Bathyuroconger parvibranchialiS : Smith, 1999:1686 (part).

Holotype. USNM 93376 (298 mm), Philippines, off northern Luzon , Hermanos Id. (N), 18.54°N, 122.02°E, 421 m, Albatross sta. 5326, 12 Nov. 1908.

Paratypes. Indonesia: USNM 93372 (1, 497), Moluccas, between Gillolo & Makayan Id., 0.20°N, 127.49°E, 527 m, Albatross 5624, 29 Nov 1909 . Philippines: USNM 93377 (1, 275+), off northern Luzon , 18.55°N, 127.37°E, 388 m, Albatross sta. 5329, 19 Nov 1908 . USNM 93379 (3, 135‒186), off northern Luzon , 18.57°N, 121.85°E, 410 m, Albatross sta. 5325, 12 Nov. 1908 . USNM 441776 (2, 145‒155), same data as USNM 9336 .

Diagnosis. A species of Bathyuroconger with a very small gill opening, preanal length 36.9‒39.8 %TL, predorsal length 14.5‒15.9 %TL, predorsal vertebrae 12‒14, preanal vertebrae 47‒52, total vertebrae 173‒178. Bathyuroconger fowleri is distinguished from all other species except B. parvibranchialis by the very small gill opening, separated from the pectoral-fin base by a distance greater than the diameter of the gill opening (vs less than diameter of gill opening). It is distinguished from B. parvibranchialis by the position of the dorsal-fin origin (over base of pectoral fin vs behind base of fin); a greater preanal length (vs 33.3‒37.1 %TL), greater predorsal length (vs 12.6‒14.5 %TL), a greater trunk to head ratio (1.7‒2.1 vs 1.4‒1.7); more predorsal vertebrae (vs 7‒10), more preanal vertebrae (vs 43‒48), and fewer total vertebrae (vs 181‒189). In addition, it appears to be somewhat smaller (largest specimen 497 mm vs 715 mm) and lives in shallower water (388‒527 m vs 432‒1022 m).

Description. Measurements in %TL: PAL 36.9‒39.8, PDL 14.5‒15.9, HL 12.3‒13.5, TR 23.4‒27.4, DA 6.1‒6.5. In % PAL: PDL 36.4‒41.9, HL 31.3‒36.6, TR 63.4‒68.7, DA 14.7‒17.0. In % HL: S 21.5‒25.6, E 12.2‒15.5, IOW 14.3‒19.9, UJ 31.9‒38.9, GO 2.8‒7.3, IB 14.6‒28.2, PL 23.4‒42.1. Pores: PALL 46, PDLL 9‒12, PPLL 6, SO 3, IO 5, POM 10, ST 1. Vertebrae: PDV 12‒14, PAV 47‒52, PCV 52‒55, TV 173‒178.

Body moderately slender, cylindrical anteriorly, compressed and tapering posteriorly. Trunk short, trunk length 1.7‒2.2 times head length. Tail slender but not filamentous, anus at about anterior third of total length. Dorsal and anal fins confluent with caudal, dorsal fin begins approximately over middle of pectoral fin, anal fin begins immediately behind anus; pectoral fin moderately well developed. Head large, rounded, deeper than body, jaws equal. Snout short and blunt, rounded in dorsal view, about 1.5‒2.0 times eye diameter. Eye moderately small, over posterior part of upper jaw, its posterior margin approximately at level of rictus; interorbital space relatively broad, its width greater than eye diameter. Anterior nostril tube like, at front of snout; posterior nostril in front of mid-eye, a simple pore. Gill opening small, located anteroventral to pectoral fin, its upper end below level of lower pectoralfin base; distance from gill opening to fin base distinctly greater than diameter of gill opening.

Vertebrae: predorsal 12‒14, preanal 47‒52, precaudal 52‒55, total 173‒178.

Head pores moderate in size, not enlarged and slit-like. Supraorbital pores 3; first pore at tip of snout, on edge of upper lip, opening downward; second pore larger, above and slightly behind first, in front of upper base of anterior nostril; third above and behind second, directly above base of anterior nostril. Infraorbital pores 5; first just behind anterior nostril; second below and behind first, about midway between anterior and posterior nostrils; third below anterior margin of eye; fourth below posterior part of eye, slightly behind mid-eye level; fifth behind rictus; no pores behind eye. Preoperculomandibular pores 10; 7 in mandibular section, 3 in preopercular, the last one at about level of first lateral-line pore. One median supratemporal pore, anterior to level of first lateral-line pore; no lateral pores. Lateral line complete, lateral-line pores large; predorsal 9‒12, prepectoral 6, preanal 46.

Teeth large and pointed. Intermaxillary teeth in two transverse rows, each with 4‒6 fang-like teeth, exposed when mouth closed. Vomer with 2 enlarged median teeth, the second larger than the first, with a few smaller teeth around and behind them, length of patch rather short. Maxillary teeth in 3 irregular rows anteriorly, narrowing to 2 rows posteriorly, the outer teeth larger. Dentary teeth in about 3‒4 rows anteriorly, biserial for most of length, the outer teeth larger, those at anterior end enlarged.

Color in preservative medium to light brown, fins with dark margin posteriorly. Smaller specimens with three longitudinal rows of small melanophores, presumably the remnant of larval pigment.

Distribution. Known from two rather widely separated localities in the tropical NW Pacific: northern Luzon in the Philippines and the Moluccas in Indonesia, depth 388‒ 527 m. There are no obvious differences between the northern and southern specimens, and it likely occurs in the intermediate area as well. Its presence in Taiwan and farther north cannot be ruled out, as its close relative B. parvibranchialis was not known north of the Philippines until the present study.

Remarks. The specimens of this species are part of the type series of Silvesterina parvibranchialis . Fowler (1934) did not notice the distinction, but it is unlikely that any of his contemporaries would have noticed either. The differences between the two species are not obvious, and they must be examined closely to be seen. The vertebral counts are particularly revealing, but at that time, the importance of this character in the identification of eels was not generally appreciated, and x-ray machines were not widely used. In addition to the number of vertebrae, the two species are distinguished by the position of the dorsal-fin origin (over the base of the pectoral fin in B. parvibranchialis but distinctly behind that point in B. fowleri ) and the position of the anus (somewhat more anterior in B. parvibranchialis than in B. fowleri , reflected in the lesser preanal length in the former). In addition, there is a distinct but difficult-to-quantify difference in the shape of the body. When compared side-by-side, B. parvibranchialis is seen to be more slender and more gradually tapering posteriorly than B. fowleri , which has a distinctly deeper-bodied appearance and tapers more abruptly to the tail. Based on the available specimens, B. fowleri is somewhat smaller; the largest specimen is 497 mm compared to 715 mm in B. parvibranchialis . Finally, B. fowleri appears to live in shallower water than B. parvibranchialis , based on the collection records of the known specimens, 388‒527 m for B. fowleri and 432‒1022 m for B. parvibranchialis .

Ideally, the largest specimen would have been chosen as the holotype, but that specimen has a damaged tail and is missing a few vertebrae at the posterior end. The second-largest specimen, USNM 93376, has a complete vertebral column and was selected on that basis.

Figures

FIGURE 4.. Scatter plots demonstrating the different mophormetric proportion of Bathyuroconger species in present study. A. gill opening height (%HL) versus preanal length. B. Head length (%PAL) versus preanal length.

FIGURE 7. Bathyuroconger fowleri sp. nov., USNM 93376, 298 mm TL.

FIGURE 8. Lateral view of head of three Bathyuroconger species. A. B. fowleri sp. nov., paratype, USNM 93372, 497 mm TL. B. B. hawaiienSiS, holotype, USNM 348215, 392 mm TL. C. B. parvibranchialiS, holotype, USNM 92346, 645 mm TL.