Symphysanodon andersoni Kotthaus 1974

Symphysanodon andersoni Kotthaus 1974

Bucktoothed Slopefish

(Figures 1, 2; Tables 1–3)

Symphysanodon andersoni Kotthaus 1974:52, fig. 326 (original description, illustration; holotype. ZMH 5170, 157 mm SL; type locality southwest of Socotra Island, near the entrance to the Gulf of Aden (11°33.9’ N, 52°54’ E to 11°38’ N, 52°52’ E), depth 290 to 190 meters).

Diagnosis. A species of Symphysanodon distinguishable from all other members of the genus by number of tubed lateral-line scales, 60 to 65 in S. andersoni, fewer than 60 in the other species. Also, in combination, the following characters distinguish S. andersoni from other Symphysanodon: parapophyses present on first caudal vertebra, total number of gillrakers on first arch 41 or 42, sum of total number of gillrakers plus lateral-line scales (in individual specimens) 101 to 106, depth of body at dorsal-fin origin 31.2 to 31.4 % SL.

Description. Morphometric data are in Table 1. Data for most countable characters follow (data for scale counts appear in Table 2); values for the holotype are indicated by asterisks for characters having variable counts. Branchiostegals 7. Dorsal-fin rays IX, 10. Anal-fin rays III, 7. Pectoral-fin rays 16 or 17.* Pelvic-fin rays I, 5. Caudal-fin rays: principal 17 (9 + 8); branched 15 (8 + 7); procurrent 13 dorsally, 12 ventrally. Gillrakers on first arch 12 or 13* + 29 (total 41 or 42*). Tubed lateral-line scales 60* to 65. Sum of total number of gillrakers plus lateral-line scales, in individual specimens, 101 to 106. 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). First caudal vertebra with parapophyses. Short neural spine on second preural centrum. Autogenous haemal spine associated with second preural centrum. Parhypural autogenous, bearing a hypurapophysis. Hypural 1 + hypural 2 present as a single unit, hypural 3 + hypural 4 present as a single unit. Hypural 5 autogenous. Epurals 3. Uroneurals 2 pairs. Epineurals associated with first 9 vertebrae. Pleural ribs on vertebrae 3 through 10. Trisegmental pterygiophores: 3 or 4 associated with posterior part of dorsal fin, 3 with posterior part of anal fin. Snout relatively blunt. Dorsalmost margin of maxilla covered by very narrow suborbital with mouth closed. Mouth terminal; lower jaw inclined dorsally with mouth closed; jaws about equal. Maxilla reaching posteriorly to vertical beyond middle of eye. Anterior and posterior nares fairly closely set. Pseudobranchiae present. Interorbital region flattened to slightly convex. Opercle with two flattened spines. Margins of both limbs of preopercle almost smooth; angle of preopercle with or without spine-like projection. 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, lateral aspects of snout, and interorbital region with scales; dorsum of snout mostly without scales. Branchiostegals and branchiostegal membranes without scales. Dorsal and anal fins without scales (except specimen of 204 mm SL with some scales on most posterior dorsal and anal-fin rays), but with 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 distinctly forked. Anterior ends of premaxillae incised, forming conspicuous notch that receives anterior ends of dentaries (see Fig. 2), anteriorly each dentary with well-developed patch of mostly exserted teeth. Premaxilla with outer series of small teeth and inner band of much smaller granular teeth; premaxillary notch toothless, but some of teeth on either side of notch exserted in holotype (well developed patch of exserted teeth on either side of notch in 204-mm-SL specimen, see Fig. 2). Dentary with series of small conical teeth extending from elevated posterodorsal surface of jaw almost to symphysis; numerous teeth at anterior end of jaw adjacent to symphysis and on elevated posterodorsal surface of jaw somewhat enlarged; many enlarged teeth at anterior end of jaw exserted and fitting into premaxillary notch when mouth closed. In 204-mm SL specimen, teeth in exserted patches at anterior ends of upper and lower jaws mostly incisor like to molariform, some of these teeth conical to subconical. Vomer and palatines with teeth; vomerine tooth patch small, semicircular or triangular, without posterior prolongation; palatine teeth in longitudinal band. No teeth seen on tongue or pterygoids.

......continued on the next page Coloration. In specimen caught off Oman (Fig. 1): Head mostly reddish. Dorsum of body yellow, overlain by red orange beneath dorsal fin and on caudal peduncle; body beneath lateral line mainly rosy. Iris of eye red adjacent to pupil. Spines in dorsal fin yellow, interspinous membranes pale violet; soft dorsal fin mostly yellow, red on distal portions of posterior dorsal soft rays. Pectoral, pelvic, and anal fins mainly pallid, with some rose. Caudal fin mainly yellow, with considerable orange and red orange dorsally and posteriorly.

Comparisons. Number of tubed lateral-line scales distinguishes S. andersoni (with 60–65) from all other species of Symphysanodon (variously with 42–59). Sum of total number of gillrakers plus number of lateral-line scales (in individual specimens) distinguishes S. andersoni (with 101–106) from all other species of Symphysanodon except S. xanthopterygion (with 94–101). In addition, S. andersoni has parapophyses on the first caudal vertebra, whereas the Atlantic species S. berryi, S. mona, and S. octoactinus, the Pacific species S. maunaloae and S. parini, and the Indian Ocean species S. rhax lack those processes. In Table 3, we compare selected characters of Indian-Ocean species of Symphysanodon.

Distribution. Known from southwest of Socotra Island, near the entrance to the Gulf of Aden, and from the Arabian Sea off the south coast of Oman.

Holotype: ZMH 5170, 157 mm SL; near mouth of Gulf of Aden, about 60 nautical miles off Socotra, northwestern Indian Ocean; 11°33.9' N, 52°54' E to 11°38' N, 52°52' E; METEOR station 102; depth 290 to 190 meters; 20 December 1964.

Other material: USNM 435866, 204 mm SL; off Raysut Port, Salalah, Dhofar, Sultanate of Oman, Arabian Sea, northwestern Indian Ocean; 16°55’39” N, 54°01’18” E; depth ca. 80 meters; collected by S. R. Al Shajibi, 16 April 2014.