Symphysanodon xanthopterygion, Anderson, William D., 2011

Anderson, William D., 2011, A new species of the perciform fish genus Symphysanodon (Symphysanodontidae) from the Arabian Sea off the southwestern coast of India, Zootaxa 2966, pp. 31-36 : 32-35

Symphysanodon xanthopterygion , new species

Indian Bunquelovely, Indian Slopefish ( Figures 1 , 2 ; Tables 1–3 )

Material examined. COLLECTION I— 5 specimens, 127–145 mm SL; off Quilon, India, Kerala Coast, southeastern Arabian Sea; 09°05’ N, 75°52’ E; 240 meters; collected by K.K. Bineesh and K.V. Akhilesh, 0 8 September 2010. COLLECTION II— 10 specimens, 119–146 mm SL; off Quilon, India, Kerala Coast, southeastern Arabian Sea, 09°20’ N, 75°51’ E; 150–220 meters; collected by K.K. Bineesh and K.V. Akhilesh, 17 September 2010.

Holotype. From COLLECTION II: USNM 400886, 141 mm SL.

Paratypes. From COLLECTION I: DNR GB. 31.146.1.2, DNR GB. 31.146.1.2.1, DNR GB. 31.146.1.2.2— 3 specimens, 127–131 mm SL; GMBL 10-016, one specimen, 136 mm SL; USNM 400887, one specimen, 145 mm SL. From COLLECTION II: CMFRI /PFD/SYM/8.1-8.8, 8 specimens, 119–146 mm SL; UF 180312, one specimen, 137 mm SL.

Diagnosis. A species of Symphysanodon distinguishable from the other species of the genus by the following combination of characters. First caudal vertebra with parapophyses. Total gillrakers on first arch 38 to 42. Lateralline scales 54 to 59. Sum of lateral-line scales plus total number of gillrakers on individual specimens 94 to 101. Head length 33 to 37% SL. Head depth 18 to 21% SL. Snout length 5 to 6 % SL. Body depth 24 to 27 % SL. Lower caudal-fin lobe bright yellow; bright yellow spot usually present on posterior part of opercle.

Description. Morphometric data appear in Table 1 . Data for countable characters follow (some of which also appear in Table 2); values for the holotype are indicated by asterisks for characters having variable counts (data for some osteological characters not available for holotype). Branchiostegals 7. Dorsal-fin rays IX, 10. Anal-fin rays III, 7. Pectoral-fin rays 16* to 18 (17 *). Pelvic-fin rays I, 5. Caudal-fin rays: principal 17 (9 + 8); branched 15 (8 + 7); procurrent 12 or 13 dorsally, 11 to13 ventrally. Gillrakers on first arch 11 to 13 (12*) + 27 to 30*—total 38 to 42*. Tubed lateral-line scales 54 to 59* (58*). Sum of total number of gillrakers plus lateral-line scales, in individual specimens, 94 to 101* (100*). No spur on posteriormost ventral procurrent caudal-fin ray, but penultimate ventral procurrent caudal-fin ray shortened basally (see Johnson, 1975). Vertebrae 25 (10 precaudal + 15 caudal). Formula for configuration of supraneural bones, anterior neural spines, and anterior dorsal pterygiophores 0/0/0 + 2 + 1/1/1/—using notation of Ahlstrom et al. (1976:297). First caudal vertebra with parapophyses. Neural spine of second preural centrum short. Autogenous haemal spine associated with second preural centrum. Parhypural autogenous, bearing a hypurapophysis. Hypurals 1 and 2 fused, hypurals 3 and 4 fused. Hypural 5 autogenous. Epurals 3. Epineurals associated with first 9 or 10 vertebrae. Pleural ribs on vertebrae 3 through 10. Trisegmental pterygiophores: 3 associated with dorsal fin, 2 or 3 with anal fin.

Snout blunt. Anterior ends of premaxillae incised, forming a notch that receives anterior ends of dentaries. Dorsalmost margin of maxilla covered by very narrow suborbital with mouth closed. Mouth terminal, oblique; premaxillae protrusile; jaws about equal. Maxilla reaching posteriorly to vertical beyond middle of eye. Anterior and posterior nares fairly closely set on each side of snout. Pseudobranchiae present. Interorbital region flattened to very slightly convex. Opercle with two flattened spines. Both limbs of preopercle rarely serrate, margins usually smooth, occasionally slightly roughened; angle of preopercle with short spine, spine-like process, a few serrae, or occasionally smooth. Dorsal fin continuous and not incised at junction of spines and segmented rays. Scales ctenoid (with ctenial bases in posterior fields proximal to marginal cteni—see Hughes, 1981; this is the transforming ctenoid scale of Roberts, 1993). Most of head, including maxillae, dentaries, lachrymals, dorsal and lateral aspects of snout, and interorbital region scaly. Branchiostegals and branchiostegal membranes naked; most of gular region naked, but with some scales anteriorly. Dorsal and anal fins naked (except some scales present proximally on posteriormost soft rays), but with low scaly sheaths at their bases; pectoral and pelvic fins scaly basally; both lobes of caudal fin scaly. Large modified scales associated with pelvic fin, just dorsal to pelvic spine (axillary scales) and in ventral midline between the pelvic fins (interpelvic scales). Lateral line gently curved beneath dorsal fin. Caudal fin well forked.

Premaxilla with outer series of small conical teeth and inner band of extremely small teeth; anteriorly teeth in outer series considerably enlarged; premaxillary notch toothless. Dentary with series of small conical teeth extending from elevated posterodorsal surface of bone almost to symphysis; numerous teeth adjacent to symphysis and on elevated posterodorsal surface of jaw conspicuously enlarged; some enlarged teeth at anterior end of dentary exserted, extending anterior to premaxillary notch when mouth closed; symphysis toothless. Vomer and palatines with extremely small teeth; vomerine tooth patch chevron shaped, without posterior prolongation; palatine teeth in narrow band. Endopterygoids without teeth. No evidence of teeth on tongue, but tongue with numerous papillae.

Coloration. Head mostly red orange, usually with bright yellow patch on posterior part of opercle; body red orange dorsally, pallid ventrally; iris of eye mainly yellow; dorsal fin yellow to orange; pectoral fin rosy; pelvic and anal fins pallid; upper lobe of caudal fin orange to red, lower lobe bright yellow.

Comparisons. Symphysanodon xanthopterygion can be distinguished from all other described species of Symphysanodon except S. typus by number of tubed scales in the lateral line— 54 to 59 in S. xanthopterygion vs. 42 to 52 (60 or 61 in S. andersoni ); the range of counts of lateral-line scales in S. typus (49 to 55) overlaps slightly the range for S. xanthopterygion (Table 2). The range of sums of total numbers of first-arch gillrakers plus numbers of tubed lateral-line scales in individual specimens is 94 to 101 in S. xanthopterygion , distinguishing it from all other species except S. typus , which has a slightly overlapping range of 86 to 94 (Table 2). The ranges for a number of morphometric characters (in percentages of standard length) in S. xanthopterygion differ (or overlap only slightly) with those of S. andersoni and S. typus ( Table 3 ).

The photograph included with the account of S. typus in Kimura et al. (2003:46) shows a fish with a yellow patch on the posterior part of the opercle, yellow lower caudal-fin lobe, and overall light rosy coloration. The coloration of S. xanthopterygion is similar, but the yellow on the lower caudal-fin lobe is brighter and the general body coloration is redder.

Heemstra et al. (2006) reported and illustrated (p. 454, figure 7G) a species of Symphysanodon , observed and photographed from a submersible off Ngazidja (Grand Comoro) Island, writing (p. 453): “Our photograph and video tapes show a pinkish purple fish, with a bright yellow spot on the opercle; the lower caudal fin lobe is yellow and the upper lobe is pink with a white tip; the dorsal fin is hyaline yellow.” The yellow on opercle and lower caudal-fin lobe is reminiscent of S. xanthopterygion , but the overall body coloration is not.

Distribution. This species is known from the southeastern Arabian Sea off the Kerala Coast of southern India. The specimens reported herein were collected off Quilon in 150 to 240 meters of water.

Remarks. As can be seen in Figure 2 , S. xanthopterygion is numerous in collections made off Quilon and is common (along with Nemipterus ) in the local fishery, being sold in the domestic market.

Symphysanodon xanthopterygion and S. typus are quite similar in morphology and coloration (see Comparisons above and Tables 2 & 3) and have nonoverlapping geographic ranges ( S. typus being widely distributed in the Pacific from Hawaii to the Philippines and Indonesia), suggesting that the two species constitute a sister group and that the range of a more continuously distributed ancestor may have been split by a barrier formed in the Indo- Malaysian Region.

Etymology. The name xanthopterygion is from the Greek—xanthos (yellow), pterygion (fin)—referring to the yellow coloration of the lower caudal-fin lobe. The specific name of the new species is a noun in apposition to the generic name Symphysanodon .

TABLE 2. Frequency distributions in three species of Symphysanodon for total numbers of gillrakers on first gill arch, numbers of tubed lateral-line scales, and sums of total gillrakers plus lateral-line scales in individual specimens. Counts of gillrakers and lateral-line scales are presented for both sides of the holotype of S. andersoni , the only specimen of that species examined.

Total numbers of gillrakers on first gill arch

36 37 38 39 40 41 42 Mean

andersoni 1 1

typus 6 6 7 1 2 37 .41 xanthopterygion 1 3 7 2 2 40.07

Numbers of tubed lateral-line scales

49 50 51 52 53 54 55 56 57 58 59 60 61 Mean

andersoni 1 1

typus 2 1 4 4 5 2 1 52.00 xanthopterygion 1 2 3 __ 4 3 57.00

Sums of total numbers of first-arch gillrakers plus numbers of tubed lateral-line scales in individual specimens

86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 Mean

andersoni 2

typus 2 3 __ 3 2 3 2 __ 2 89.71 xanthopterygion 3 1 1 2 3 1 1 1 97.00 S . xanthopterygion S. typus S. andersoni

Figures

FIGURE 1. Holotype of Symphysanodon xanthopterygion, USNM 400886, 141 mm SL; southeastern Arabian Sea, Kerala Coast, off Quilon, India. Photographed by Sean Money, Charleston Museum.

FIGURE 2. Freshly caught Symphysanodon xanthopterygion, southeastern Arabian Sea, Kerala Coast, off Quilon, India. Photographed by K. K. Bineesh.

Tables

TABLE 1. Morphometric data on Symphysanodon xanthopterygion. Standard lengths in mm, other measurements in percentages of standard length;> = slightly damaged.

Measurement	n	Range Holotype	Measurement n	Range	Holotype
Standard length Head, length Head, depth Snout, length	15 15 15 15	119–146 141 33.2–36.5 35.0 18.4–20.5 19.8 5.1–6.2 6.0	Caudal peduncle, length 15 Anal fin, length of base 15 Depressed anal fin, length 15 Pectoral fin, length 15	24.0–26.6 13.2–16.0 24.0–27.8 23.5–29.4	24.3 14.9 25.2 29.4
Fleshy orbit, diameter Postorbital length of head	15 15	8.1–9.6 9.6 17.6–21.3 17.8	Pelvic fin, length 15 Upper caudal–fin lobe, length 13	20.5–24.3>29.1–47.3	23.2 ca. 39.3
Suborbital width Cheek, height Maxilla width Upper jaw, length Lower jaw, length Bony interorbital, width	15 15 15 15 15 15	0.24–0.87 0.57 5.7–7.0 6.7 4.0–5.6 4.2 13.6–15.0 14.4 14.0–15.2 14.8 6.1–7.9 7.1	Lower caudal–fin lobe, length 13 First dorsal spine, length 15 Second dorsal spine, length 13 Third dorsal spine, length 15 Fourth dorsal spine, length 14 Last dorsal spine, length 15	>28.4–40.4 4.3–6.3 7.8–9.4 9.8–11.6 10.8–13.1 11.1–13.0	ca.36.4 6.0 9.1 10.7 12.5 11.7
Internarial distance Predorsal–fin length Body, depth Caudal peduncle, depth	15 15 15 15	0.60–0.93 0.71 33.9–35.6 35.5 23.8–27.4 27.0 8.8–10.5 9.8	Longest dorsal spine, length 15 First anal spine, length 15 Second anal spine, length 15 Third anal spine, length 15	11.4–13.5 3.8–5.9 8.1–9.4>9.8–11.6	12.7 (5th) 4.2 9.2 11.5