Echelus polyspondylus McCosker & Ho

Ho, Hsuan-Ching, 2015, New species of the snake eels Echelus and Ophichthus (Anguilliformes: Ophichthidae) from Taiwan, Zootaxa 4060 (1), pp. 71-85 : 73-76

Echelus polyspondylus McCosker & Ho , sp. nov.

Many-vertebrae snake eel

Figures 1–3 ; Table 1

Holotype. NMMB-P 14218 (537 mm), female, Dong-gang, Pingtung, southwestern Taiwan, South China Sea [collected from the fish landing ground near Dong-gang fish market], ca. 200 m, 5 Sep. 2010, coll. H.-C. Ho.

Paratypes. 6 specimens, 331–561 mm TL. Collected from near the type locality: NMMB-P 16638 (331 mm), male, 28 Feb. 2012. NMMB-P 16639 (460 mm), 14 Nov. 2012. CAS 236966 (375 mm), female, 11 Jun. 2013. Collected from Da-xi, Yilan, NE Taiwan: ASIZP 63164 (3 spec., 418–561 mm), 1 Mar. 2003, partially dried and twisted specimens.

Diagnosis. An elongate species of Echelus with: tail 65–69%, head 7.6–8.3%, and body depth at gill opening 1.8–2.3% of total length; tail tip flexible, caudal-fin rays covered by skin, but confluent with dorsal and anal; dorsal-fin origin nearly 1 head length behind gill opening; pectoral fin pointed, not elongate and well-developed; posterior nostril within upper lip, opening into mouth; pores small, inconspicuous, SO 1+4, IO 4+2, POM 6+3; teeth small, numerous and conical, biserial on jaws, uniserial on vomer; coloration tan dorsally, pale ventrally, fins pale except anal-fin membrane which is black before tail tip; total vertebrae 172–183, mean vertebral formula 20- 53-177.

Counts and measurements of the holotype (in mm). Total length 537; head 41.6; trunk 141.4; tail 354; predorsal distance 82; pectoral-fin length 5.8; pectoral-fin base 1.7; body depth ca. 11.5 at gill openings; body width ca. 10.8 at gill openings; body depth at anus 11.8; body width at anus 11.8; body depth at branchial basket 14.4; snout 7.5; tip of snout to rictus 14.2; snout overhang beyond tip of lower jaw 0.7; eye diameter 4.1; interorbital width 5.0; gill opening height 3.0; isthmus width 6.8. Right preanal lateral-line pores 58 (66 in left side), total pores 174. Vertebral formula 21-55-181.

Description. Body elongate ( Fig. 1 ), subcircular to mid-trunk, then becoming more compressed, its depth at gill openings 43–55 in TL. Branchial basket slightly expanded. Head 2.9–3.5 in trunk. Head and trunk 2.9 and head 12.0– 13.1 in TL. Snout rounded when viewed from above, its underside not bisected by a short groove. Lower jaw included, its tip reaching to middle of base of anterior nostril tube. Upper jaw not elongated, rictus slightly behind a vertical from posterior margin of eye. Eye not enlarged, 2.9–4.1 in upper jaw and 10–15 in head. Anterior nostrils tubular, extending ventrolaterally from snout at ca. 45o, reaching below upper lip but not extending below chin. Posterior nostril a hole within upper lip, covered by a flap that is not cut along upper lip. No barbels along upper lip. Dorsal-fin origin well behind pectoral fin, nearly a head length into trunk length. Median fins low, collapsible into a shallow groove and meeting and extending slightly beyond the flexible tail tip. Pectoral fins pointed, not elongate, slightly shorter than snout.

Head pores small, inconspicuous ( Fig. 2 ). Single median interorbital and temporal pores. Supraorbital pores 1+4, infraorbital pores 4+2, lower jaw pores 6, preopercular pores 3, supratemporal pores 5. Lateral-line pores inconspicuous; 9–10 before gill opening in an arching sequence, 22–25 before dorsal-fin origin, 56–60 before anus, except for 66 in one side of the holotype; total pores 171–178, the last pore ca. 3 times snout length before the tail tip.

Teeth ( Fig. 3 ) small, conical, numerous and slightly retrorse. One central ethmovomerine tooth flanked by 6–8 uniserial teeth, followed by an irregular row of 30–35 small vomerine teeth, decreasing in size posteriorly. Maxillary teeth irregularly biserial anteriorly, the outer row about 50 smaller teeth, the inner row about 30–40 teeth. Lower jaw with about 35–40 pairs of irregularly biserial teeth, the inner row slightly smaller.

Coloration in life tan dorsally, pale ventrally beneath lateral line ( Fig. 1 ). Coloration in ethanol uniform pale brown dorsally, white ventrally. Tail uniform tan. Snout, chin, and anterior nostrils tan. Median and pectoral fins, inside of mouth, anal opening, and peritoneum pale. Anal-fin membrane notably black about 1 head length in advance of pale tail tip.

Size. The largest known specimen is 561 mm TL.

Etymology. From the Greek poly (many), and spondylos (vertebrae), in reference to its having more vertebrae than any of its congeners.

Distribution. Known from the type series, collected from off Dong-gang fishing port, SW Taiwan at a depth around 200 meters, and from Da-xi, NE Taiwan.

Remarks. The new species appears to be most similar to Echelus uropterus ( Temminck & Schlegel, 1846) , its only Indo-Pacific congener, which is known from 120–380 m depth from east Africa and the Mozambique Channel to Australia, Tonga, Taiwan and Japan. The most recent synonymy of E. uropterus is provided by McCosker (in press a). They differ in their meristics, morphology, and coloration. Echelus polyspondylus has more vertebrae (172–183 vs. E. uropterus 150–162), a shorter head (12–13 in TL vs. 8.3–8.7 in TL), a more posterior dorsal-fin origin (one head length behind gill openings vs. above pectoral-fin tips), and in its coloration (dorsal-fin margin clear before tail tip vs. black before tail tip) ( Karrer, 1983; McCosker in press a).

The new species is similar to its eastern Atlantic congeners Echelus myrus ( Linnaeus, 1758) and E. pachyrhynchus ( Vaillant, 1888) but differs in having more vertebrae ( Echelus polyspondylus 172–183 vs. E. myrus 149–155 and E. pachyrhynchus 149–157) and in being more elongate (43–55 in TL vs. 24–35 and 17–24 in TL) (McCosker, in press b). They apparently occupy similar depths: E. myrus occupies 3–150 m and E. pachyrhynchus at 200–500 m ( Blache, 1968; McCosker, in press b).

Holotype Paratypes Echelus polyspondylus , E. uropterus , and Scolecenchelys fuscapenis McCosker, Ide & Endo, 2012 are the only relatively shallow-water Taiwanese ophichthids that have melanistic median fins just prior to their tail tips. This condition was proposed by McCosker et al. (2012) as a means to strengthen the tail region of tail-burrowing eels. Small specimens of slender Ophichthus , Myrophis , and certain Neenchelys might be mistaken for Echelus polyspondylus , however they are easily separable on the basis of the black coloration of the anal fin of E. polyspondylus prior to the tail tip.

There are a few more pores on the left side of the holotype which may be attributed to individual variation.

Figures

FIGURE 1. Echelus polyspondylus McCosker & Ho, sp. nov., holotype, NMMB-P 14218, 537 mm TL. Bars indicate the origins of the dorsal fin (left) and anal fin (right). A. Lateral view of whole fish. B. Lateral view of left head.

FIGURE 2. Semi-diagrammatic illustration of lateral head of Echelus polyspondylus McCosker & Ho, sp. nov., from the holotype. Arrows point to the frontal pore (left) and median pore of supratemporal series (right).

FIGURE 3. Semi-diagrammatic illustration of dentition of Echelus polyspondylus McCosker & Ho, sp. nov., from the holotype. A. Upper jaw. B. Lower jaw.

Tables

TABLE 1. Counts and proportions (in thousandths) of the type series of Echelus polyspondylus sp. nov.

TL (mm)	537	331–561 (n=6)
		mean Range
HL/TL	77	80 76–83
Head and trunk/TL	341	334 340–346
Trunk/TL	263	261 245–275
Tail/TL	659	676 654–690
Dorsal fin-origin/HL	153	151 139–160
Pectoral fin-length/HL	139	163 139–202
Pectoral fin-base/HL	25	30 24–33
Upper jaw/HL	341	288 215–341
Snout/HL	180	192 180–207
Eye/HL	99	86 65–104
Gill opening/HL	72	67 62–72
Isthmus/HL	163	134 101–171
Depth at gill opening/TL	21	21 18–23
Width/depth at gill opening	940	880 750–980
Vertebral counts
Predorsal vertebrae	21	20.2 19–21
Preanal vertebrae	55	52.8 50–55
Total vertebrae	181	176.8 172–183