Muraenichthys thompsoni, Jordan & Richardson, 1908

Hibino, Yusuke, Ho, Hsuan-Ching & Mccosker, John E., 2019, A new species of Muraenichthys (Anguilliformes: Ophichthidae) from Taiwan with redescription of Muraenichthys thompsoni Jordan & Richardson, 1908, Zootaxa 4702 (1), pp. 41-48 : 44-48

Muraenichthys thompsoni Jordan & Richardson, 1908

(English name: Thompson’s Worm Eel) (New Japanese standard name: Shino-mimizu-anago) (Taiwanese name: Ḁ Kƃǿ)

Muraenichthys thompsoni Jordan & Richardson, 1908: 237 (Manila Bay, Luzon, Philippines); Allen & Erdmann 2012: 106 (Manila Bay, Luzon, Philippines); McCosker 2014: 339 ( Philippines); Ho et al. 2015: 169 ( Taiwan); Hibino 2017: 31 (Panay Island, Philippines); Hibino 2018: 22 (Ha Long Bay, Vietnam).

Muraenichthys malabonensis Herre, 1923: 157 (Bañgos pond at Malabon, Rizal Province, Manila Bay, Philippines); McCosker 2014: 339 ( Philippines; with question); Hibino & Kimura 2015: 63, table 1 (only key characters).

Material examined. 64 specimens, 48–267 mm TL: SU 20201 , holotype , 96.5 mm TL, Manila Bay, Luzon, Philippines; BPBM 37185, 202 mm TL, Maumere Bay , Flores, Indonesia, depth 3–4 m; FRLM 4244 , 48 mm TL, Zagashima island , Shima, Mie, Japan, depth 2–3 m (excluded from description because of the small body); KAUM-I . 69442, 69445, 69447, three specimens, 102–178 mm TL, Panay , Philippines; KMNH VR 100226, 209 mm TL, Dong-gang, Taiwan; MNHN 1965-340, 207 mm TL, southwestern coast of Madagascar; MUFS 43869, 267 mm TL, Kadogawa, Miyazaki, Japan; NMMB-P 12488, 144 mm TL, Phen Thiet, Vietnam; NMMB-P 17508, 175 mm TL, NMMB-P 30619, 219 mm TL, Dong-gang, Taiwan; PMBC 20588, 166 mm TL, Ao Nambor, Phuket, Thailand; PMBC 21061, 189 mm TL, Lanta Yai Island , Krabi, Thailand; SU 60966 , 19 specimens, 86–158 mm TL, Tolo Channel , Hong Kong, China; SU 61117 , 4 specimens, 98–164 mm TL, Hong Kong, China; USNM 259666 , 55 mm TL, Naqara Island , Fiji, depth 0.9 m; USNM 259672 , 25 specimens, 63–151 mm TL, Naqara Island , Fiji, depth 0.9 m (smaller specimens less than 70 mm TL excluded from description); USNM 401024, 207 mm TL, Nha Trang, Vietnam .

Diagnosis. A species of the genus Muraenichthys with the following combination of characters: head 12–15% TL, tail 57–64% TL; dorsal-fin origin anterior to a vertical through mid-anus, horizontal distance from the origin to the vertical 42–64% of trunk length; eyes large, 6.6–10% HL; snout to interorbital region not concaved along dorsal midline; all teeth relatively slender and pointed, rows uniserial or biserial anteriorly and uniserial posteriorly; vomer relatively slender; predorsal vertebrae 24–32, preanal 42–46 and total 128–138; MVF 27-44-134.

Description. Counts and measurements are shown in Table 1 . Body long, subcylindrical, its depth at gill opening 21.3–40.0 in TL ( Figs. 3 , 4 ); tail compressed posteriorly, its depth slightly reduced posteriorly.

Figures in parentheses indicate mean values and sample size, respectively *Data from Herre (1923)

Head large, branchial basket weakly expanded; head 6.5–8.3 and head and trunk 2.3–2.8 in TL; snout robust, rounded, its length equal to more than twice eye diameter; ventral groove on snout absent; lower jaw included in upper jaw, its tip beyond anterior base of anterior-nostril tube; mouth large, rictus well behind a vertical from posterior margin of eye and slightly behind a vertical through posteriormost infraorbital pore, along with a groove reaching to end of jaw; eye moderate in size, 10.1–15.2 in HL, covered by a transparent skin; mid-eye located anterior to above mid-jaw (mid-point between tip of snout and end of maxilla); anterior nostril tubular, its length slightly shorter than eye diameter, somewhat anteriorly directed; inner opening of posterior nostril above upper lip, and outer opening of posterior nostril located above upper lip, anteroventral to eye, a slit-like opening towards down side with a short flap anteriorly; lips smooth or with scattered small papillae; interorbital region smooth, convex but usually without a groove or an extremely shallow depression; gill opening constricted, located ventrolaterally.

Dorsal and anal fins low, slightly elevated in posterior tail region, ending confluent with caudal fin; dorsal fin originating about mid-trunk but variable, about 1/3 to 3/5 of trunk; caudal fin prominent, its tip rounded; pectoral fin absent.

Head pores small but obvious; arrangement of sensory pores on head as follows: one + four on supraorbital; three + two on infraorbital, one between anterior and posterior nostrils; six on mandible and three on preopercle; midtemporal and interorbital pores present.

Lateral-line pores developed to posterior tail, 11–13 in branchial basket, 23–26 anterior to dorsal-fin origin, 42–46 anterior to anus, and 84–110 in total, generally smaller specimens less developed than larger.

All teeth relatively slender and pointed; teeth on jaws generally uniserial (including holotype), rarely biserial anteriorly ( Fig. 5C, D ); vomerine teeth uniserial or biserial anteriorly, one to three teeth uniserial posteriorly (including holotype); intermaxillary teeth slightly larger than others, arranged in a semicircular rosette of five teeth (in holotype) or a tooth patch.

Color of head and body of fresh specimens ( Fig. 3 ) brown to pale brown, darker and yellowish in posterior tail. Dorsal and anal fins pale whitish brown but becoming darker and yellowish before tip of tail; caudal fin yellowish dark brown. Color (once preserved in 50% isopropyl alcohol or 70% ethanol) of head and body dark brown to pale brown, with numerous dark melanophores on dorsal surface, lower half of head to anterior tail portion weakly paler. Fin coloration mostly the same as when fresh but yellowish color is faded.

Distribution and ecological note. Widely distributed in Indo-Pacific, known from Madagascar, western coast of Thailand, Vietnam, Philippines, Indonesia ( Flores Sea), Hong Kong, Taiwan, Japan, and Fiji Islands. It is a shallow water species, found in rocky tide pools or shallow sandy and muddy bottoms usually <100 m.

Remarks. Muraenichthys thompsoni and M. malabonensis were described based on specimens collected from Manila Bay, Philippines. All syntypes of M. malabonensis were deposited at the Department of Agriculture, Bureau of Science, Manila, Philippines, and were destroyed during World War II (Fricke et al. 2019). Therefore the taxonomic status of M. malabonensis has been uncertain ( McCosker 2014). Herre (1923) provided the key to Philippine species of Muraenichthys and stated that M. thompsoni and M. malabonensis can be distinguished by their arrangement of vomerine teeth (“vomer with two rows of teeth” vs. “vomer with teeth in one row, imperfectly two rowed or forming a Y”) and the proportional length of eye diameter in head length (“eye 18 in head” vs. “eye 11 to 14 in head”). In the present examination, the holotype of M. thompsoni has small biserial teeth on the vomer anteriorly, but uniserial posteriorly. Moreover, the proportion of the eye diameter based on McCosker’s measurement is 9.8 in HL. The holotype of M. thompsoni has a larger head than that of the syntypes of M. malabonensis , but the range of head length is very wide in M. thompsoni , and the range of M. gymnopterus which is the most similar species is also very wide. Consequently, these morphological differences between two nominal species can be regarded as intraspecific variation, and we conclude that M. malabonensis is a junior synonym of M. thompsoni .

Most of the present specimens identified as M. thompsoni were formerly identified as Muraenichthys sp. or M. gymnopterus . Although M. thompsoni and M. gymnopterus resemble each other, the former differs from the latter in the position of the dorsal-fin origin (horizontal distance from the origin to a vertical through mid-anus 42–64% of trunk length vs. 29–48%), eye diameter (6.6–10% HL vs. 3.2–7.1%), tooth rows on the maxilla (one or two anteriorly and one posteriorly vs. two or more; Fig. 5 ), and the shape of the vomerine teeth (pointed and relatively slender vs. blunt and robust). Although M. thompsoni has been hitherto known only from the holotype collected in the Philippines, we now expand its range to Madagascar to Fiji, and north to Japan.

Comparative materials. Muraenichthys gymnopterus : AMS I. 4399, 184 mm TL, Luzon, Philippines; AMS I.39103-002, 236 mm TL, Viti Levu Island, Fiji; ASIZP 72203, Tainan, Taiwan; SU 38864, 148 mm TL, Dumaguete, Negros, Philippines; USNM 135156, 209 mm TL, Luzon, Philippines; USNM 135157, 181 mm TL, Luzon, Philippines; USNM 135158, 229 mm TL, Luzon, Philippines. Specimens of M. gymnopterus are those listed in Hibino & Kimura (2015).

Figures

FIGURE 3. Fresh condition of Muraenichthys thompsoni, KMNH VR 100226, 209 mm TL, Dong-gang, Taiwan. A, whole body; B, enclosed view of head.

FIGURE 4. Holotype of Muraenichthys thompsoni, SU 20201, 97 mm TL, Manila Bay, Luzon, Philippines. A, enclosed view of head; B, whole body.

FIGURE 5. Teeth arrangement on maxilla and palatal areas of Muraenichthys gymnopterus (A, B) and M. thompsoni (C, D). A, USNM 243005, 222 mm TL, Batanta Island, Indonesia; B, KAUM-I. 20909, 147 mm TL, western Bengal; C, MNHN 1965-340, 207 mm TL, southwestern coast of Madagascar; BPBM 37185, 202 mm TL, Maumere Bay, Flores, Indonesia.

Tables

TABLE 1. Counts and measurements of Muraenichthys thompsoni.

	Holotype SU 20201	Syntypes of Muraenichthys malabonensis * (n =4)	Other specimens (n =63)
Total length (mm)	96	117–193	48–267 (134.1)
Counts
Lateral-line pores before anus	-	-	42–46 (44.1, 27)
Predorsal vertebrae	29	-	24–32 (27.4, 56)
Preanal vertebrae	43	-	42–46 (43.9, 56)
Total vertebrae	131	-	128–138 (134.1, 56)
Measurements
As % of total length
Head length	15	13–15 (14.0)	12–15 (13.6, 33)
Trunk length	27	26	23–27 (24.7, 33)
Tail length	57	60–62 (60.3)	59–64 (61.5, 33)
Predorsal length	30	-	20–29 (26.0, 33)
Body depth at gill opening	3.8	-	2.5–4.7 (3.9, 27)
Body width at gill opening	2.6	-	1.5–3.4 (2.4, 27)
As % of trunk length
Dorsal-fin origin to anus	46	ca. 50	42–64 (49.7, 33)
As % of head length
Dorsal-fin origin to anus	82	-	72–116 (90.3, 33)
Upper-jaw length	-	-	35–46 (39.9, 33)
Length of mouth gape	26	29–38 (31.9)	24–33 (29.6, 33)
Snout length	11	-	9.5–15 (12.0, 33)
Eye diameter	10	7.1–9.1 (8.3)	6.6–9.9 (8.2, 33)
Interorbital width	7.5	-	5.0–11 (8.8, 33)
Gill-opening length	4.8	-	3.1–11 (6.2, 33)