Dysomma goslinei Robins & Robins, 1976

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 : 94-96

Dysomma goslinei Robins & Robins, 1976

Table 2

Dysomma goslinei Robins & Robins, 1976:261 (type locality: Indian Ocean, 14°52'N, 96°39'W). Robins & Robins, 1989:249. Smith, 1999:1661. Chen & Mok, 2001:79.

Diagnosis. Pectoral fin present; dorsal-fin origin before pectoral-fin base, predorsal length 10.7% TL; anus anterior, just below pectoral fin, preanal length 16.2% TL; trunk very short, trunk length 4.0% TL; no intermaxillary teeth; multiple rows of teeth on upper jaw; 4 compound teeth on vomer; teeth on lower jaw multiserial, those on inner row slightly enlarged; lateral line short; and MVF 10-15-123. [Data adapted from Chen & Mok, 2001].

Remarks. No specimen from Taiwan is available for this study. Mok in Shen et al. (1993) first recorded the present species from Taiwan, but no voucher was mentioned. One specimen (NSYSU 2607, 207 mm TL) examined by Chen & Mok (2001) has only 123 total vertebrae, less than 130–131 provided by Robins & Robins (1989). However, we could not locate this specimen. More investigations are needed of the population in Taiwan.

Dysomma longirostrum Chen & Mok, 2001:79 (type locality: Nan-fang-ao, NE Taiwan). Ho & Shao, 2011:22 .

Specimens examined. Holotype: NSYU 2732 (196), Nan-fang-ao fish market, NE Taiwan, bottom trawl, 100–150 m, 12 Sep. 1992, coll. Y.- Y. Chen.

Other locality. MNHN 2003-1515 (1, 285), R/V Alis, stn. CP8, 24°54'S, 168°21'E, Norfolk Ridge, New Caledonia, Coral Sea, 540 m, 11 Aug. 1999.

Diagnosis. Pectoral fin present; origin of dorsal fin above tip of pectoral fin, predorsal length 17.9–18.6% TL; no intermaxillary teeth; snout very long, its length 25.7–32.1% HL; jaw long and slender, upper jaw length 42.0– 52.1% HL; anus posterior, far behind pectoral fin, preanal length 24.0–24.3% TL; trunk moderately long, trunk length 9.7–10.3% TL; multiple rows of teeth on upper jaw; 5 compound teeth on vomer; multiple rows of small teeth on lower jaw, those on inner row larger than the rest; head pores: SO 5, IO 8 (2 between nostrils, 2 below eye, 4 behind eye), M 7, POP 2, AD 1, ST 0, F 1; lateral-line pores: predorsal 11, prepectoral 3–6, preanal 20, total ca. 77 or ca. 96, the last at 2/3 HL before caudal fin; MVF 14-24-130 (holotype only). Body uniformly brown when preserved. [Data adapted from Chen & Mok, 2001 and based on present study].

Remarks. One additional specimen was found in the MNHN collection that represents the second record of the species, in New Caledonia.

Dysomma longirostrum is the only member with four head pores behind the eye and two POP pores among all congeners. There is one frontal pore in the holotype whereas the MNHN specimen has none. The count of total lateral-line pores is not accurate because the posterior portion of the lateral line (behind anus) is broken into small canals, each canal connects two pores. These canals are not evenly spaced and sometimes have additional pores in the space between two canals. However, this may be used as a diagnostic character because the other congeners examined in the present work all have a continuous lateral line.

Tables

TABLE 2. Morphometric and meristic data of Dysomma goslinei, Dysomma longirostrum and Dysomma melanurum. Data of D. goslinei and morphometric data of D. longirostrum are adapted from Chen & Mok (2001).

D. goslinei	D. longirostrum	D. melanorum
	Holotype Non-type
Total length (mm) 197	196 283	206–297 (n=13)
% TL		Mean (range)
Head length 12.2	14.3 14.1	12.2 (11.0–13.4)
Predorsal length 10.7	17.9 18.6	13.8 (11.5–15.0)
Preanal length 16.2	24.0 24.3	16.2 (15.4–17.3)
Trunk length 4	9.7 10.3	4.0 (3.0–5.3)
Tail length 83.8	76 75.7	83.8 (82.7–84.6)
Depth at gill opening –	– 6	2.8 (2.2–3.2)
Depth at anus 4.6	5.1 6.5	3.0 (2.4–4.0)
Width at anus –	– 3.5	1.8 (1.0–2.6)
%HL
Snout length 20.8	32.1 25.7	16.6 (13.8–19.2)
Eye diameter 4.2	7.1 8.8	6.7 (5.4–9.1)
Interorbital width –	– 15.8	5.9 (3.9–7.5)
Upper jaw length 41.7	57.7 42.0	41.1 (36.2–45.3)
Interbranchial width –	– 16.6	4.6 (2.4–6.1)
Vertebrae		n=12
Predorsal 10	14 –	12–13
Preanal 15	24 –	13–15
Total 123	130 –	131–138
Lateral-line pores –		n=13
Preanal –	20 20	11–17
Total –	ca.96 ca.77	107–117
Head pores –		n=13
Supraorbital 3	5 5	3
Infraorbital 5	8 8	4
Adnasal?	1 1	1
Mandibular 6	7 7	7 (1 with 8)
Preopercular –	2 2	0
Supratemporal –	0 0	0
Frontal –	1 1	0
Vomerine teeth 4	5 5	5 or 6
Intermaxillary teeth 0	0 0	0
Dysomma longirostrum Chen & Mok, 2001 Fig. 5; Table 2