Nettenchelys proxima Smith, Lin & Chen

Smith, David G., Lin, James, Chen, Hong-Ming & Pogonoski, John J., 2015, The eels of the genus Nettenchelys, with description of a new species from Taiwan (Teleostei: Anguilliformes: Nettastomatidae), Zootaxa 4060 (1), pp. 105-120 : 114-117

Nettenchelys proxima Smith, Lin & Chen , new species

Figs. 1 a, 5–7

? Nettenchelys gephyra: Smith & Böhlke in Smith et al. 1981:555 (smaller specimen only)

Holotype. NMMST P 0 1524 (251 mm TL, immature female, egg size 0.05–0.09 mm), Donggang, Pingtung, Taiwan, bottom trawl, 22˚12’57”N, 120˚26’21”E, depth 300 m, 4 April 2002.

Other material. USNM 134972 (93 mm TL, poor condition), Philippines, ALBATROSS sta. 5187, 9˚16’45”N, 123˚21’15”E, depth 412 m, 31 March 1908.

Diagnosis. Nettenchelys proxima differs from all other species in the genus except N. gephyra and N. pygmaea in having an enlarged median series of teeth at the anterior end of the vomer. It differs from N. gephyra in having the posterior nostril immediately behind the eye (approximately midway between eye and supratemporal canal in N. gephyra ), in having 78 PCV (79–101 in N. gephyra , but 91–101 in specimens from Taiwan), and in having 9 + 2 IO pores (8–9 + 3–4 in N. gephyra ). It differs from N. pygmaea in its larger size (251 mm in the holotype, an immature female, vs. 201 mm for the largest known N. pygmaea and 151 mm for a mature female) and slight differences in some meristic and morphometric characters ( Table 1 ).

Description. Measurements of holotype in mm and percent of preanal length: predorsal 27 (31.0), head 24 (27.6), depth at anus 4.9 (5.6); in mm and percent of head length: snout 9.3 (38.8), eye 2 (8.3), upper jaw 13.5 (56.3), lower jaw 12.6 (52.5), gill opening 1.4 (5.8), interbranchial 2.2 (9.2). Meristic features: TV 185+, PDV 6, PAV 44, PCV 78, PADR 96, PALL 43, PDLL 8, IO 9 + 2, SO 5, POM 10 + 3, ST 3.

Body and head elongate; tail narrow and tapering, incomplete in holotype; anus before midlength. Dorsal and anal fins continuous around tail, dorsal-fin origin behind gill opening, anal-fin origin immediately behind anus; height of dorsal fin about half body depth. Pectoral fin absent. Snout elongate, narrow, slightly depressed, its anterior tip soft and fleshy, extending a short distance beyond intermaxillary tooth patch. Eye well developed, about midway between snout tip and gill opening. Anterior nostril tubular, near tip of snout, directed anterolaterally; posterior nostril a simple, relatively large opening on top of head immediately behind posterior margin of eye. Lateral line complete.

Preoperculomandibular canal with ten pores in the mandibular section and three pores in the preopercular: first pore on edge of lower lip at tip of jaw; second pore below and behind first, along lower lip; third through tenth pores along lower lip spaced more or less evenly between second pore and posterior end of lower jaw; eleventh to thirteenth pores in an ascending arc behind tenth, the last one below the first LL pore. Supraorbital canal with five pores: first (ethmoid) pore on underside of tip of snout; second pore on upper side of snout before anterior nostril; third pore on top of snout above and immediately behind anterior nostril; fourth on top of snout about one third of distance between anterior nostril and eye; fifth on top of snout near anterior margin of eye. Infraorbital canal with nine pores along upper jaw and two behind eye: first pore on edge of upper lip below anterior nostril directly behind middle of anterior nostril base; second pore elevated above first and directly behind anterior nostril base; third pore below and behind second, along upper lip; fourth through ninth pores on edge of upper lip spaced more or less evenly between third pore and rictus; tenth pore above and slightly behind ninth, at level of lower half of eye; eleventh pore directly above tenth at level of upper half of eye and just below posterior nostril. Supratemporal canal with three pores: one median and one on each side.

Teeth mostly small, conical, in narrow bands on jaws and vomer. Intermaxillary tooth patch about as long as wide, the inner and posterior teeth somewhat larger, continuous with maxillary teeth. Maxillary teeth in about four rows, those of the inner row larger than outer. Vomerine tooth patch elongate, extending from shortly behind intermaxillary teeth to below anterior margin of eye; first four teeth slightly separated from remainder, distinctly enlarged and forming a single median row, increasing in size from anterior to posterior, these constituting the largest teeth in mouth; remainder of teeth in an elongate, narrow band, those in middle slightly larger than those on outside. Dentary teeth in narrow bands, those of inner row larger than outer; largest dentary teeth larger than any of the maxillary teeth.

Color in preservative pale brown, fins dark-edged posteriorly.

Distribution. Taiwan and possibly Philippines. The geographic distribution of N. proxima specimens is shown in Fig. 7 .

Etymology. From the Latin proxima , near, referring to the position of the posterior nostril, close to the eye; also referring to its close resemblance to N. gephyra and N. pygmaea . An adjective.

Remarks. This new species resembles only Nettenchelys gephyra and N. pygmaea in having an enlarged series of median teeth at the anterior end of the vomer. It differs from the latter two species primarily in the characters mentioned in the diagnosis: nostril position, precaudal vertebrae, and size. It further differs from N. gephyra in PADR (96 vs. 102–112 in specimens from Taiwan), upper jaw length (56.3 vs. 49.0–55.5 % head in specimens from Taiwan), and lower jaw length (52.5 vs. 45.1–51.7 % head). It differs from N. pygmaea in PDV (6 vs. 7–8), PAV (44 vs. 40–43), PCV (78 vs. 75), postorbital pores (2 vs. 3), predorsal length (31 vs. 33–35 % preanal), and head length (27.6 vs. 30–33 % preanal). Because of the small sample size, however, it is uncertain how meaningful these minor differences are.

The second specimen listed, USNM 134972, was included in Nettenchelys gephyra by Smith et al. 1981, although they did not make it a paratype because of its small size and poor condition. We tentatively reassign it here to N. proxima because the posterior nostril seems to be closer to the eye than it is in N. gephyra , but its size and condition make its positive identification uncertain. Hence we exclude it from the type series.

Figures

FIGURE 1. Position of the posterior nostrils in nine species of the genus Nettenchelys (modified after Karmovskaya, 1999). (a) N. pygmaea, N. proxima; (b) N. gephyra and N. dionisi; (c) N. inion; (d) N. paxtoni; (e) N. exoria; (f) N. erroriensis; and (g) N. taylori.

FIGURE 7. Geographic distribution of Nettenchelys proxima, based on holotype (NMMSTP 01524) and other material (USNM 134972).