Monopterus ichthyophoides, Britz, Ralf & Lalremsanga, Hmar Tlawmte, 2011

Britz, Ralf & Lalremsanga, Hmar Tlawmte, 2011, Monopterus ichthyophoides, a new species of scaled swamp eel (Teleostei: Synbranchiformes: Synbranchidae) from Mizoram, India, Zootaxa 2936, pp. 51-58 : 52-56

Monopterus ichthyophoides new species

Figures 1–4 .

Holotype. PUCMF 3005, 186.6 mm TL; India: Mizoram, Barak River drainage, Sawleng River, a tributary of Tuirial River in the vicinity of Sawleng, 23°58’52” N 92°55’14” E; HT Lalremsanga, 14 August 2008.

Paratypes. PUCMF 3006, 2, 127.8- 180.8 mm TL; India: Mizoram, Barak River drainage, public well at Luangmual, Aizawl, 23°44’26” N 92°42’00” E; Lalrotluanga, 26 July 2008. BMNH 2011.5.3.1, 184.2 mm TL; same data as holotype.

Diagnosis. Monopterus ichthyophoides differs from all other species of synbranchids in having only 2 branchiostegal rays (vs 5–6). It differs further from all other synbranchids, except M. cuchia , M. fossorius , M. indicus , and M. desilvai by the presence of scales. It differs from the latter four species also by the number of vertebrae (79– 82 + 34–37 = 114–117 vs M. cuchia 99–112 + 55–70 = 166–188, M. fossorius 73 + 53-56 = 126–129, M. indicus 93–99 + 42–45=137–144, M. desilvai 75 +69 =144). It differs further from M. cuchia in having the scales restricted to the posterior part of its body (vs extending anteriorly up to the head) and from M. desilvai and M. indicus in having scales extending anteriorly far beyond the vent (vs. ending posterior to vent in M. desilvai and M. indicus , but with a small separate scale patch in M. indicus )

Description. For general appearance see Figures 1 and 2 . Morphometric data and vertebral counts are presented in Table 1 .

Body very elongate, eel-like, round to oval in cross section, but laterally compressed in its caudal portion. Depth 27.5–35.4 times in TL; body width 1.3–1.4 times in its depth. Head prominent, 6.1–7.3 times in TL, with bulging adductor muscles behind eye; snout anteriorly rounded in dorsal view. Eye small, covered by thick skin. Posterior naris an oblique slit above, medial to, and slightly in front of eye ( Fig. 2 a, b); anterior naris developed as small circular orifice at ventral side of upper lip ( Fig. 2 a, c). Lower lip overhung by upper lip, not visible in dorsal view. Lateral-line pores on head not developed. Skin covering branchial chamber smooth, not produced into longitudinal furrows. Gill membrane completely fused to isthmus medially, therefore gill openings reduced to a pair of small slits ventrolaterally on either side of head. Gill filaments absent on all gill arches. Only a single functional (open) gill slit, situated between gill arches three and four, guarded by a fleshy valve originating from ceratobranchial 3; other gill slits closed. No suprapharyngeal pouch evident. Hyoid with only two branchiostegal rays on posterior ceratohyal. Basibranchial 3, epibranchial 1, interarcual bone (and cartilage) and pharyngobranchial 2 absent ( Fig. 3 ); hypobranchial 2 far removed from hypobranchial 1 and basibranchial 2; ceratobranchial 1 shifted posteriorly and medially, closely associated with hypobranchial and ceratobranchial 2; ceratobranchial 5 with a row of pointed, posteriorly curved teeth on its posterior aspect; a number of pointed, curved teeth also present on pharyngobranchial 3 and on pharyngobranchial 4 toothplate.

Posterior part of body covered by numerous small, circular (cycloid) scales extending further anteriorly on dorsum (starting at 50–60% TL) than on venter (starting in front of vent at 67–71 % of TL). Vent located at around 80% of TL in a completely scaled area of the venter. All fins and their supporting skeleton absent. Vertebral counts as in Table 1 .

Coloration. In alcohol ( Figs. 1 , 2 ). Olive brown on the dorsum and upper half of sides, lighter brown on lower half of sides and venter. Myosepta visible as darker segmentally arranged lines.

In life ( Fig. 4 ). Olive-brown, lighter on sides and on venter, similar to preserved specimens.

Distribution. Known only from two localities in the Barak River drainage in Mizoram, India (Fig. 5): Sawleng River, a small stream with muddy bank and bottom (elevation 904 m above sea level) in the vicinity of Sawleng, and a public well (elevation 1006 m above sea level) with a muddy bottom at Luangmual, Aizawl.

Etymology. The name ichthyophoides is derived from the Greek ἰχθύς (ichthys), fish, and ὄφɩς (ophis), snake, and the Latin ending – oides, meaning “similar to”. It alludes to the striking superficial similarity of this species to large larvae of the caecilian genus Ichthyophis .

FIGURE 5. Map of collecting localities of Monopterus ichthyophoides ; *PUCMF 3005 holotype and BMNH 2011.5.3.1 paratype, + PUCMF 3006 paratypes.

Figures

FIGURE 1. Holotype of Monopterus ichthyophoides, PUCMF 3005, 186.6 mm TL, Sawleng River, Mizoram, India, in lateral view.

FIGURE 2. Holotype of Monopterus ichthyophoides, PUCMF 3005, 186.6 mm TL. Head in lateral (a), dorsal (b) and ventral (c) view (arrows mark position of posterior naris in a and b and anterior naris in c) and preanal area of body in lateral view (d) to show scales (arrow marks position of vent).

FIGURE 3. Cleared and stained gill arches of Monopterus ichthyophoides, PUCMF 3006, 180.8 mm, paratype, dorsal view. aCH, anterior ceratohyal; BB, basibranchial; BH, basihyal; BR, branchiostegal rays; CB, ceratobranchial; dHH, dorsal hypohyal; EB, epibranchial; PB, pharyngobranchial; pCH, posterior ceratohyal; UP 4, upper pharyngeal toothplate 4.

FIGURE 4. Live specimen of Monopterus ichthyophoides, PUCMF 3006, one of the paratypes, 30 July 2008, public well at Luangmual, Aizawl, Mizoram, India.

Tables

TABLE 1. Selected morphometric and meristic data for Monopterus ichthyophoides holotype and 3 paratypes.

Total length (TL) in mm In percent of total length	Holotype 186.6	Paratype BMNH 2011.5.3.1 184.2	Paratype PUCMF 3006 180.8	Paratype PUCMF 3006 127.8
Head length (HL) Preanal length Body depth at vent Body width at vent In percent of head length Snout length	6.3 79.2 3.2 2.4 25.6	6.5 79.5 3.6 2.8 29.2	6.1 79.2 3.0 2.2 27.3	7.3 80.1 2.8 2.0 23.7
Distance anterior-posterior naris Ratios Depth/Width of body Total length/Head lenth	29.1 1.3 15.9	29.2 1.3 15.4	30.9 1.4 16.4	25.8 1.4 13.7
Total length/Body depth	31.1	27.5	33.5	35.4
Abdominal vertebrae Caudal vertebrae Total vertebrae	80 34 114	82 26 +, damaged 108 +, damaged	79 37 116	82 35 117