Chlopsis orientalis Tighe, Hibino & Nguyen

Chlopsis orientalis Tighe, Hibino & Nguyen View in CoL , sp. nov.

Figs. 8 View FIGURE 8 , 9 View FIGURE 9 , 10 View FIGURE 10 , 11 View FIGURE 11 , 12 View FIGURE 12

Holotype. IMER 16495 (269 mm total length, male), Cua Be trawl fish landing port, Nha Trang, Vietnam, South China Sea, collected by Q. V. Nguyen, 23 April 2014.

Diagnosis. A species of the genus Chlopsis with the following combination of characters: head length short (ca. 10 % of total length), predorsal vertebrae 11, preanal 35, and total 135; body bicolored with no white stripes on head; intermuscular bones very stout.

Description. Total vertebrae 135, predorsal vertebrae 11, preanal vertebrae 35, precaudal vertebrae 49, dorsal rays 432, anal rays 436, dorsal rays anterior to anal-fin origin 88. Proportions as percent of total length: predorsal length 12.4, preanal length 29.0, head length 9.9, body depth at gill opening 3.2, body depth at anus 3.5. Proportions as percent of head length: eye diameter 13.6, interorbital width 15.1, snout length 24.5, tip of snout to rictus 34.0, tip of lower jaw to rictus 30.6.

Body elongate, relatively stout; trunk cylindrical, and tail compressed strongly, depth almost constant, distinctly tapering in last 10% of total length to tip of tail ( Fig.8 View FIGURE 8 ). Dorsal-fin origin well behind gill opening, horizontal distance from a vertical through posterior margin of gill opening to origin almost equal to snout length. Head relatively small; dorsal profile of head convex at a level of middle of eye; interorbital region convex with mid-dorsal groove. Snout moderate in length, broad. Gape short, rictus of mouth reaching to posterior margin of eye. Anterior nostril tubular, slightly behind tip of snout, directed anterolaterally. Posterior nostril oblong, a posteroventrally directed low tubular opening (completely concealed by a thick dermal flap) on lip in front of eye. Eyes large, elliptic and slightly oblique.

Lateral line on body absent except for one pore in branchial region, anterior to gill opening ( Fig. 9 View FIGURE 9 ). Supraorbital pores three: first (ethmoidal) at anteroventral tip of snout, second anteromedial to base of anterior nostril, and last above and behind anterior nostril. Infraorbital pores four: first just posterior to anterior nostril, second midway between anterior and posterior nostrils, third just behind posterior nostril, and last below posterior edge of eye. Preoperculomandibular pores five, first near tip of lower jaw and last just before posterior edge of eye, anterior to rictus.

Maxillary teeth ( Fig. 10 View FIGURE 10 ) slender, and recurved posteriorly, arranged in two rows; inner row larger than outer, ca. 18 in inner row and ca. 35 in outer. Mandibular teeth conical and broad, arranged in two irregular rows anteriorly and a single row posteriorly, ca. 32–37 teeth total on each side of jaw; anterior and inner teeth slightly enlarged. Intermaxillary teeth conical and broad, with ca. 18 arranged in scattered tooth patch with 1 additional tooth connecting to vomerine teeth. Vomerine teeth relatively large, in two longitudinal series of 21–22 teeth in each row, relatively close-set anteriorly, diverging slightly near middle of vomerine tooth rows and then converging near the end of tooth rows.

Color (fresh specimen) of body distinctly bicolored, dark grayish-brown dorsally and light cream ventrally, the border through about middle of body before anus, falling gradually toward tip of tail, and ending about half of head length before tip of tail. Dorsal and caudal fins dark grayish-brown, anal fin light cream mostly, dark brown in tip of tail.

Etymology. The name is derived from the Latin orientalis , “of the east” and refers to the type locality in the Far East.

Distribution. Known only from the holotype collected by fishermen apparently working in the Thuy Trieu coastal lagoon near Nha Trang, Vietnam; presumably more widespread along the coast of Vietnam.

Remarks. Chlopsis orientalis is similar in overall appearance to several other members of the genus Chlopsis that are bicolored including the following five species: Chlopsis apterus ( Beebe & Tee-Van, 1938) ; Chlopsis bicollaris ( Myers & Wade, 1941) ; Chlopsis bicolor Rafinesque, 1810 ; Chlopsis bidentatus McCosker & Tighe 2003 ; Chlopsis kazuko Lavenberg 1988 ; Chlopsis nanhaiensis (described herein). Chlopsis orientalis differs from C. bidentatus in having two rows of teeth on the vomer (vs. four rows anteriorly) and 135 total vertebrae (vs. 125– 128). Chlopsis orientalis can be distinguished from C.apterus , C. bicollaris , and C. kazuko by its shorter head (ca. 10 % TL vs. 11–16 %), from C. apterus and C. bicollaris by its fewer preanal vertebrae (35 vs. 39–43), from C. bicollaris and C. kazuko by the position of the dorsal-fin origin (distinctly behind a vertical through posterior margin of the gill opening vs. before or slightly behind), and from C. apterus and C. bicollaris by the presence of white stripes on the head (no white stripes on the head vs. white stripes on the snout or dorsal side of the gill basket). Chlopsis orientalis can be distinguished from C. sagmacollaris by the distinct coloration of the latter species (lightly bicolored with darker patch on nape) and lower vertebral number (135 vs. 142). Chlopsis orientalis is most similar to C. bicolor in body coloration, meristics and morphometrics, but can be distinguished from the latter species by several characters. First, although similar in coloration pattern, the distinction between dorsal and ventral pigmentation is greater in C. bicolor with the dorsal being dark brown and the ventral very white while C. orientalis is dark grayish brown with a light cream colored ventral ( Fig. 11 View FIGURE 11 ). Also, C. orientalis has fewer preanal vertebrae than C. bicolor (35 vs. 39–42). Third, there is a distinct difference in the size of the intermuscular bones in C. orientalis . Figure 12 View FIGURE 12 shows a comparison of the trunk vertebrae of C. bicolor and C. orientalis . As can be seen, the intermuscular bones of C. bicolor are thin and needle-like while those of C. orientalis are much heavier and stouter. Other species in the genus Chlopsis can be distinguished from C. orientalis by coloration. Chlopsis olokun , from the eastern Atlantic, is a fairly uniform tan or gray color, while C. dentatus (from the Atlantic and Indian Oceans) and C. slusserorum (from the southwestern Pacific) have banded, blotched or mottled coloration.