Meadia minor Vo & Ho, 2021

Vo, Van Quang, Ho, Hsuan-Ching, Dao, Ha Viet & Tran, Hoa Hong Thi, 2021, A new arrowtooth eel of genus Meadia (Synaphobranchidae: Ilyophinae) from Vietnam, South China Sea, Zootaxa 4952 (1), pp. 181-191 : 182-185

Meadia minor Vo & Ho , sp. nov.

urn:lsid:zoobank.org:act:9B9DF84B-6EDC-4381-99F4-6BC225B181A3

English name: Small arrowtooth eel

Figs. 1 , 2 ; Table 1

Holotype. OIM-E. 55801, 307 mm TL, field no. Q.00443-2, ca. 13°44’N, 109°15’E, off Quy Nhon , Binh Dinh, central coast of Vietnam, South China Sea, bottom trawl, ca. 100–120 m, 3 May 2019.

Paratypes. Nine specimens, 273–330 mm TL, all collected from near type locality: NMMB-P37412 , 3 specimens, 278–292 mm TL, 2 May 2019 ; OIM-E.55802, 4 specimens, 298–330 mm TL, 2 May 2019; OIM-E. 55803, 316 mm TL, 3 May 2019; OIM-E. 55804, 273 mm TL, 3 May 2019.

Diagnosis. A species of scaleless ilyophine eel of the genus Meadia with a relatively long trunk (21.3–25.0% TL) that is longer than head length; a short and blunt snout (21.4–23.7% HL); interbranchial space broad (20.7– 26.2% HL); gill opening against lower base of pectoral-fin base; dorsal-fin origin above posterior third of pectoral fin; body depth 24–28 times in TL; TV 118–122; mean vertebral formula 7-33-121; and a small body size reaching 330 mm TL.

Description. Morphometric data of the holotype, in mm (% TL in parentheses). TL 307; head length 35.1 (11.4% TL); predorsal length 36.6 (11.9); preanal length 104 (33.9); trunk length 68.9 (22.4); tail length 203 (66.1); depth at gill opening 12.6 (4.1); width at gill opening 10.4 (3.4); depth at anus 10.6 (3.5); width at anus 10.2 (3.3); eye diameter 3.6 (1.2); interorbital width 9.2 (3.0); snout length 7.5 (2.4); upper-jaw length 14.4 (4.7); gill opening height 1.9 (0.6); pectoral-fin length 8.8 (2.9).

The following values are given for the holotype, followed by that of all types in parentheses. Body moderately slender, body depth at gill opening 24 (24–28) times in TL; head and trunk slightly compressed, becoming more compressed posteriorly. Body depth relatively uniform, depth at gill opening 4.1% (3.6–4.1%) TL, narrowing gradually to caudal fin. Dorsal and anal fins high, the height of both fins about 1/4 of body depth without fins, continuous with a small caudal fin. Pectoral fin well-developed, lower half of its base at posterior-dorsal corner of gill opening; pectoral-fin length 25.1% (21.1–25.1%) HL.

Head moderately long, its length 11.4% (10.6–11.4%) TL; origin of dorsal fin slightly behind the gill opening, above a vertical through posterior 1/3 of the pectoral fin (middle to posterior 1/3 of the fin), predorsal length 11.9% (11.1–12.0%) TL; trunk long, 22.4% (21.3–25.0%) TL; anus well posterior, 2.0 (1.9–2.4) times head length behind pectoral-fin base; preanal length 33.9% (32.1–35.6%) TL; tail long, tail length 66.1% (64.4–67.9%) TL.

Head moderately slender, with a bump in the dorsal profile; snout blunt anteriorly and broad dorsally, covered with scattered short papillae; snout length 21.4% (21.4–23.7%) HL; tip of snout slightly projecting beyond lower jaw; eye moderately large, covered by a thick and semitransparent membrane, its anterior margin above middle of upper jaw (directly above to slightly behind); eye diameter 10.8% (8.3–10.9%) HL or 2.0 (2.0–2.8) times in snout length; interorbital space broad, flat or slightly concave, width 21.1% (19.9–22.1%) HL; postorbital space broad. Anterior nostrils tubular, directed anteroventrally; posterior nostril an elliptical slit without rim, situated in front of eye, about same level as lower margin of eye. Lower jaw shorter than upper, its tip reaching first pore of supraorbital series. End of mouth gape well behind eye, upper-jaw length 41.0% (38.4–41.1%) HL.

Gill opening small, oval, its posterior margin against lower half of pectoral-fin base. Head pores large and obvious ( Fig. 2A ). Head pores: SO 3 (including ethmoid), all restricted to anterior portion of snout, opening of first pore directed ventrally; AD 0; IO 4, 2 pores between nostrils, 1 below posterior nostril and last 1 below middle of eye, no pores behind eye; POM 7, anterior 6 pores along lower jaw, the last pore about 1.5–2.0 eye dimeters behind the penultimate one and rictus; ST 0; F 0.

Lateral line almost complete, the canal extends nearly to the caudal fin base; pores large and clear in anterior half of lateral line, gradually becoming smaller and indistinct. Lateral-line pores: PDLL 4 (3–4), PPLL 2 (2–3), PALL 39 (35–41).

Teeth various in size and shape ( Fig. 2B ). Teeth on intermaxillary and vomer forming a long, continuous patch extending to behind rictus; teeth on anterior margin small, large and stout on anterior half of patch, in about 7 rows at broadest portion, each with a cutting edge on tip, gradually becoming 2 well-separated rows in posterior portion. Maxillary with a short band of 3 to 4 regular rows of slender teeth, those in outer row shortest, gradually longer posteriorly; those on inner row long canines, with their tips less pointed. Lower jaw with a tooth patch longer than that of upper jaw, 3 rows anteriorly and gradually becoming 2 rows posteriorly; teeth on anterior half of inner 2 rows enlarged, each with a cutting edge, gradually becoming smaller posteriorly; teeth on outer row uniformly small.

Vertebrae: PDV 7 (6–8), PAV 32 (32–35), PCV 45 (44–46), TV 122 (118–122), and MVF 7-33-121.

Coloration. When fresh ( Figs. 1B, C ), body uniformly grayish brown; dorsal and anal fins with narrow white margins; posterior portion of tail and vertical fins darker; white patches on lips, lower parts of chin, and outer surface of gill chamber; pectoral fin pale stained with some dark pigments. When preserved, upper half of body light brown and lower half blackish brown; lip, chin, and outer surface of gill chamber irregularly pale; dorsal fin and upper part of caudal fin deep brown with very narrow white margin; anal fin dark brown, with slight white margin, on anterior half. Peritoneal membranes and mouth cavity white.

Distribution. Known from the type specimens collected from off Quy Nhon, around central coast of Vietnam, South China Sea, collected by bottom trawl at estimated depth of 100– 150 m.

Size. The largest specimen examined is a 330 mm TL male (OIM-E.55802. 1 of 4). Another mature female (OIM-E.55802, 1 of 4, 298 mm TL) has developed ovaries containing small eggs, which indicates that this is a small species.

Etymology. The specific name is from Latin minor , meaning “rather small,” in reference to the small adult body size of the species compared to two congeners, as well as most members of Ilyophinae .

Comparison. Meadia minor can be easily separated from its two congeners, as well as most members of Ilyophinae , in having a relatively long trunk (1.9–2.4 HL) and preanal length (32.1–35.6% TL), relatively few vertebrae (118–122), and more numerous teeth on premaxilla and vomer which form a continuous long patch ( Fig. 2B ).

Table 1 provides the morphometric and meristic data for comparison of the three congeners in Meadia . Meadia roseni has the highest counts of predorsal, preanal, precaudal, and total vertebrae, compared to those of M. abyssalis and M. minor . The preanal length is longest in M. minor , moderately long in M. roseni (22.0–23.5% TL) and relatively short in M. abyssalis (15.5–18.2% TL). The head and predorsal length are relatively long in M. roseni , whereas M. minor and M. abyssalis have relatively small heads and similar predorsal lengths. The snout is short in M. minor (21.4–23.7% HL), whereas both M. abyssalis and M. roseni have a relatively long snout (28.4–31.6% HL and 28.0–31.2% HL, respectively). The gill opening is relatively small in M. minor compared to that of both M. abyssalis and M. roseni .

The numbers of head pores are somewhat different among the three Meadia species. Meadia roseni has an additional SO pore above the eye, whereas the two other species do not ( Table 1 ). Both M. abyssalis and M. roseni have 1 adnasal pore at the dorsoposterior corner of the anterior nostril and 1 pore behind the eye, whereas M. minor lacks these two pores ( Table 1 ). Meadia roseni has a total of 10 or 11 pores on POM, whereas M. abyssalis has 8 pores and M. minor has 7. It is notable that the last POM pore is far behind the rictus, usually about 1.5–2.0 eye diameters in distance in all three species. The configuration of lateral-line pores is also different among these congeners and is associated with their vertebral formulae.

Moreover, the type series of M. minor includes at least one mature female which indicates that it is a small species (up to 330 mm TL). The largest specimen of M. roseni in NMMB-P collection is 723 mm TL (NMMB-P29943) and the largest specimen of M. abyssalis examined by us is 595 mm TL (NMMB-P20654).

Although included in Meadia , M. minor is also similar to Ilyophis arx , from the tropical eastern Pacific, in having a blunt head, a short and deep snout, and similar body proportions. It can be distinguished from the latter in having 35–41 preanal pores (vs. 26–30), teeth on jaws, intermaxillary, and vomer various in size (vs. mostly small and uniform in size), last POM pore clearly behind rictus (vs. below the posterior end of rictus), 118–122 total vertebrae (vs. 131–135). Meadia minor differs from the remaining species of Ilyophis in having much fewer vertebrae (vs. 140–188 in the other 4 species of Ilyophis ).

Figures

FIGURE 1. Meadia minor sp. nov. A. Holotype, OIM-E.55801, 307 mm TL, preserved. B. Paratype, OIM-E.55803, 316 mm TL, fresh caught. C. Close-up of head, from OIM-E. 55803. Arrows point to the dorsal-fin origin (D) and anal-fin origin (A).

FIGURE 2. Illustrations of Meadia minor sp. nov. demonstrating (A) the arrangement of head and anterior lateral-line pores and (B) teeth on jaws; both from holotype.