Dysomma dolichosomatum Karrer, 1983

Ho, Hsuan-Ching, Smith, David G. & Tighe, Kenneth A., 2015, Review of the arrowtooth eel genera Dysomma and Dysommina in Taiwan, with the description of a new species (Anguilliformes: Synaphobranchidae: Ilyophinae), Zootaxa 4060 (1), pp. 86-104 : 93-94

Dysomma dolichosomatum Karrer, 1983

Figs. 4 A–B; Table 1

Dysomma dolichosomatum Karrer, 1983:93 (type locality: Madagascar, 22°25'S, 43°04.5'E, 550–555 m). Robins & Robins, 1989:249. Chen & Mok, 2001:79.

Specimens examined. Collected from Fong-gang, SW Taiwan: NMMB-P2861 (1 spec., 242 mm TL), 8 Nov. 2001. Collected from Dong-gang fishing port, SW Taiwan: NMMB-P9098 (1, dry), 13 Jun. 2008. NMMB-P9241 (1, 349), 18 Sep. 2008. NMMB-P11121 (6, 209–312), 16 Jul. 2009. NMMB-P11130 (2, 231–269), 13 Sep. 2010. NMMB-P12066 (1, 336), 28, Jan. 2011. NMMB-P13794 (1, 197), 21 Jul. 2011. NMMB-P14189 (4, 166–301), 20 Oct. 2011. NMMB-P15568 (2 of 4, 218–294), 25 Oct. 2011. NMMB-P16134 (1, 189), 9 Feb. 2012. NMMB- P16404 (4, 264–320), 28 Jan. 2012. NMMB-P16422 (1, 357), 21 Feb. 2012. NMMB-P17820 (1, 357), 2 Nov. 2012. NMMB-P17881 (1, 263), 25 Jan. 2012. NMMB-P18083 (1, 336), 7 Sep. 2012. NMMB-P21733 (2, 215– 221), 18 Feb. 2011. NMMB-P21799 (1, 227), 7 Nov. 2013. NMMB-P21928 (1, 343), 1 Nov.2014. NMMB-P22126 (1, 242), 12 Dec. 2013. USNM 270682 (2, 172–187), 23 Nov. 1969. USNM 398567 (1, 317), 10 Nov. 2009. USNM 401019 (1, 197), 26 Feb. 2011. USNM 401036 (1, 345), 8 Nov. 2009.

Other localities. Madagascar: MNHN 1979-0004, holotype, 22°25'1.2"S, 43°4'4.8"E, 550–555 m, 27 Nov. 1973. Philippines: MNHN 1978-0717, paratype, 14°1'1.2"N, 120°22'1.2"E, 223 m, 21 Mar. 1976. Solomon Islands: MNHN 2006-0734 (1, 203), 8°24'28.8"S, 159°28'22.8"E, 105–897 m, 24 Oct. 2004.

Diagnosis. No pectoral fin; dorsal-fin origin about 0.8–1 HL behind gill opening, predorsal length 16.5–19.1% TL; anus posterior, about 1.5 time of HL behind gill opening, preanal length 23.3–28.6% TL; trunk long, trunk length 14.3–17.7% TL; two intermaxillary teeth; 2 irregular rows of small blunt teeth on upper jaw; 2 or 3 (mainly 3) compound teeth on vomer; single row of 4 or 5 small compound teeth followed by 1 or 2 irregular rows of small blunt teeth on lower jaw; short cirri on surfaces of chin and jaws; head pores: IO 4, SO 3, M 6 (1 with 7), POP 1, AD1, F 0, ST 0; lateral-line pores large, prepectoral 5 or 6, total 9–11, the last at slightly beyond the gill opening posteriorly; MVF 18-27-153, total vertebrae 146–156.

Body light pinkish to light grayish dorsally when fresh with a black margin at posterior portion of anal fin; light brownish to grayish when preserved.

Distribution. Indo-west Pacific off Madagascar, Taiwan, Philippines, and Solomon Islands at depth 105– 897 m.

Remarks. This species is common in the by-catch in Taiwan. It is usually collected by midwater trawlers together with many mesopelagic fishes, which would indicate pelagic living. However, many specimens are also found to feed on polychelids, a demersal shrimp family. Dysomma dolichosomatum is the only species found to possess one preopercular pore and a very short lateral line, with only 9–11 pores, among all Taiwanese species. It is similar to D. brevirostre , D. muciparus and D. tridens in lacking a pectoral fin. It differs from D. brevirostre by having tiny papillae on the head and snout (vs. large papillae and ridges) and total vertebrae 146–156 (vs. 195–205 in Robins & Robins, 1989); from D. muciparus by having trunk 1.4–1.9 times in head length (vs. less than 1 time in head length) and 146–156 total vertebrae (vs. 153–157); and from D. tridens by having 2 intermaxillary teeth (vs. three large compressed teeth) and by having 146–156 total vertebrae (vs. 175).

Our specimens have a broader range of total vertebrae (146–156) compared to 151–152 reported for the types by Karrer (1983). One 312 mm specimen out of NMMB-P 11121 had a relatively long predorsal measurement (23.4 % of TL) and high predorsal vertebral count (25 vertebrae). While it is possible that this specimen may represent a different species, the close correspondence of all other counts and measurements with the other specimens of D. dolichosomatum from Taiwan indicates that it is probably a specimen with an aberrant dorsal origin.

Figures

FIGURE 4. Dysomma dolichosomatum Karrer, 1983. NMMB-P 11130. A. 269 mm TL. B. 231 mm TL. Collected from Dong-gang fishing port.