Odontamblyopus rebecca, Edward O. Murdy & Koichi Shibukawa, 2003

Edward O. Murdy & Koichi Shibukawa, 2003, Odontamblyopus rebecca, a new species of amblyopine goby from Vietnam with a key to known species of the genus (Gobiidae: Amblyopinae)., Zootaxa 138, pp. 1-6 : 2-6

Odontamblyopus rebecca sp. nov.

(Fig.1; Tables 1-2)

Holotype: ROM 72279 , 141.0 mm SL, male.

Paratypes: AMS I.41549-001 , 2: 110.8-125.6 mm SL; MNHN 2002-3010 , 1:78.5, MNHN 2002-3011 , 1:89.0, MNHN 2002-3012 , 1: 92.0 mm SL; ROM 72625 , 2:96.1- 136.8 mm SL; ROM 72626 , 26:75.1-132.6 mm SL; USNM 369736 , 3:113.1-137.8 mm SL.

All material was collected on 29 February 2000 by Richard Winterbottom from a fish market located on the east side of Haiphong City , Vietnam (20º52' N, 106º41' E).

Diagnosis. Odontamblyopus rebecca can be diagnosed from congeners by the following combination of characters: total dorsal-fin elements 44-48 (mean 45.8), anal-fin elements37-42 (mean 38.5), pectoral fin with 40-51 rays (mean 45.8), and caudal vertebrae 20-21 (mean 20.1). A brownish streak courses from the dorsal surface of the head along dorsum to the caudal fin; chin blackish; caudal fin blackish.

Description. Counts of holotype given first, followed by those of paratypes in parentheses. D VI (VI), 40 (38-42), first non-spinous dorsal-fin ray segmented and branched; spinous dorsal-fin pterygiophore formula 3-12210 (holotype and all paratypes); dorsal fin connected by membrane to the caudal fin. Anal-fin rays 38 (37-42), first element of anal fin segmented but not branched. Anal fin connected by membrane to caudal fin. Pectoralfin rays 45/45 (40-51), all pectoral-fin rays segmented, occasionally one or more ventralmost rays branched, all others unbranched; for distal half of fin, membranous connection lacking so that rays are free and silk-like. Pelvic-fin rays I, 5; frenum present; interradial membrane uniting fins present throughout length of innermost rays. Caudal fin with 17 (17) segmented rays including 8+7 (8+7) branched rays and a dorsal and ventral simple ray.

Scales cycloid, embedded, non-imbricated, and difficult to discern without magnification; present on body and head, largest posteriorly. Head scales most abundant on dorsum with some scales on cheeks and a few on operculum. Two lateral rows of teeth in each jaw, more than two rows anteriorly; outer-row teeth much larger and more pointed than those of inner rows; lower-jaw teeth longer than upper-jaw teeth; 19 (7-20) fang-like teeth in outer row of upper jaw, typically interlocking with those of lower jaw; numerous conical teeth on inner rows of upper jaw; 9 (6-10) fang-like teeth in outer row of lower jaw; numerous conical teeth in inner rows of lower jaw. Two (occasionally only one) stout caninoid teeth internal to symphysis of lower jaw. No palatine or vomerine teeth present.

Precaudal vertebrae 10 (10), caudal vertebrae 20 (20-21).

Coloration. Head and body tannish brown. Chin with diffuse blackish blotch. Dorsal surface of head dusky brown as is dorsal-fin base almost to the caudal peduncle. From midpoint of caudal fin posteriad, blackish. Other fins translucent.

Distribution. Known only from a single locality, a fish market located on the east side of Haiphong City, Vietnam. The collector of these specimens, Dr. Richard Winterbottom, assumes the specimens were obtained along the Gulf of Tonkin coast, which is near the market, or in a nearby estuarine environment. Nguyên (1991) reported an unidentified species of Odontamblyopus from coastal provinces in northern Vietnam and stated that the species possessed: VI, 39-42 dorsal-fin rays; 37-41 anal-fin rays; 43-50 pectoral-fin rays; 10+19 (18-20) vertebrae. With the exception of the caudal vertebral count, we believe that Nguyên's description is a match with the subject specimens. (As we do not know Nguyên's methodology for counting vertebrae, we cannot be sure that our counting methods are the same.) Unfortunately, attempts to contact Mr. Nguyên were unsuccessful so his specimens were not available to us.

Etymology. This species is named for Rebecca Rootes, the life partner and spouse of the first author.

Comparisons with congeners. The following data and information pertaining to Odontamblyopus , excepting the new species described herein, were taken from Murdy and Shibukawa (2001) unless otherwise cited. With respect to O. rebecca , O. roseus differs in having a chocolate-brown distal margin on the median fins (vs. translucent in O. rebecca ); more caudal vertebrae (22 in O. roseus vs. typically 20 in O. rebecca ) and in having a longer pelvic fin (pelvic-fin length/SL 0.124-0.151, mean = 0.141, in O. roseus vs. 0.074- 0.126, mean = 0.107, in O. rebecca ). In comparison to O. rubicundus , O. rebecca has more caudal vertebrae (20-21 in O. rebecca vs. 17 in O. rubicundus ); a longer pectoral fin with respect to head length (pectoral-fin length/head length 0.673-1.050, mean = 0.852, in O. rebecca vs. 0.628-0.965, mean = 0.719, in O. rubicundus ); and fewer anal-fin pterygiophores anterior to the first hemal spine (typically 2 in O. rebecca vs. 3 in O. rubicundus ). Whereas there is considerable overlap in most meristic values between O. rebecca and O. lacepedii , a significant difference exists in the number of pectoral-fin rays (40-51, mean = 45.8, in O. rebecca vs. 24-33, mean = 27.9, in O. lacepedii ). Several morphometric measures also serve to distinguish O. rebecca from O. lacepedii : SL/TL (range 0.761-0.829, mean = 0.788, in O. rebecca vs. 0.808-0.850, mean = 0.825, in O. lacepedii ); pelvic-fin length/head length (range 0.508-0.842, mean = 0.703, in O. rebecca vs. 0.665-1.08, mean = 0.810, in O. lacepedii ); and pectoral-fin length/SL (range 0.093-0.154, mean = 0.130, in O. rebecca vs. 0.082-0.132, mean = 0.101, in O. lacepedii ).

Within the genus Odontamblyopus , only O. tenuis and O. rebecca have pectoral-fin ray counts greater than 39; the average pectoral-fin ray count for O. tenuis is 59.5 (range = 46-65) whereas for O. rebecca it is 45.8 (range = 40-51). (No other species of Odontamblyopus has more than 33 pectoral-fin rays.) We hypothesize that the shared possession of high numbers of pectoral-fin rays connotes a greater degree of relatedness between these two species than with species that do not possess this feature.

In contrast with O. rebecca , O. tenuis has barbels on the underside of the chin ( O. rebecca has none). O. tenuis typically has fewer elements in both the dorsal and anal fins than does O. rebecca (range of dorsal-fin elements 40-42, mean = 40.4, in O. tenuis vs. range of 44-48, mean = 45.8, in O. rebecca ; range of anal-fin elements 32-35, mean = 33.2, in O. tenuis vs. range of 37-42, mean = 38.5, in O. rebecca ). O. tenuis and O. rebecca differ in vertebral numbers; O. tenuis has 17 caudal vertebrae whereas O. rebecca typically has 20. Epineurals are present from 1st precaudal vertebra to the 5th caudal vertebra in O. tenuis , and 1st precaudal vertebra to the 4th, 5th, 6th, or 7th caudal vertebra in O. rebecca .

The following morphometric measures also show differences between the two species: head length/SL (range of 0.078-0.130, mean = 0.114, in O. tenuis vs. 0.130-0.179, mean = 0.152, in O. rebecca ); head width/SL (0.040-0.059, mean = 0.054, in O. tenuis vs. 0.062- 0.110, mean = 0.083, in O. rebecca ); and pectoral-fin length/SL (0.084-0.119, mean = 0.102, in O. tenuis vs. 0.093-0.154, mean = 0.130, in O. rebecca ).

Key to the species of Odontamblyopus

(modified from Murdy and Shibukawa, 2001)

1a. Pectoral-fin rays 40 or more .......................................................................................... 2

1b. Pectoral-fin rays 33 or fewer ......................................................................................... 3

2a. Chin with numerous small barbels; pectoral-fin rays 46-65; total dorsal-fin elements 40-42; anal-fin elements 32-35; 17 caudal vertebrae. (Pakistan, Myanmar) .... O. tenuis

2b. Chin lacking barbels; pectoral-fin rays 40-51; total dorsal-fin elements 44-48; anal-fin elements 37-42; 20-21 caudal vertebrae. (Vietnam) ........................ O. rebecca sp. nov.

3a. In preservative, distal margins of dorsal and anal fins tinged chocolate-brown; dorsal surface of skull bony lacking portions of adductor mandibulae muscle; epineurals present from 1st precaudal vertebra to 10th caudal vertebra. (west coast of India) .......... .......................................................................................................................... O. roseus

3b. In preservative, distal margins of dorsal and anal fins the same color as rest of fin but not chocolate-brown; dorsal surface of skull covered by adductor mandibulae muscle; epineurals present from 1st precaudal vertebra to 3rd, 4th, or 5th caudal vertebra ............ 4

4a. Caudal fin very long, standard length typically less than 80% of total length; total dorsal-fin elements 40-47; anal-fin elements 33-40; caudal vertebrae 17; 3 anal-fin pterygiophores preceding first hemal spine. (east coast of India, Bangladesh, Myanmar) .... .................................................................................................................. O. rubicundus

4b. Caudal fin long, standard length more than 80% of total length; total dorsal-fin elements44-54; anal-fin elements 36-45; caudal vertebrae 20-24; 2 (rarely 3) anal-fin pterygiophores preceding first hemal spine. (China, Hong Kong, Taiwan, Korea, Japan) ...................................................................................................................... O. lacepedii