Symphysanodon disii Khalaf and Krupp, 2008

Anderson, William D., Baranes, Avi & Goren, Menachem, 2011, Redescription of the perciform fish Symphysanodon disii (Symphysanodontidae) from the Gulf of Aqaba, Red Sea, with comments on S. pitondelafournaisei and sexual dimorphism in the genus, Zootaxa 3027, pp. 1-8 : 2-6

Symphysanodon disii Khalaf and Krupp, 2008

Disi’s Slopefish

( Figures 1 , 2 ; Tables 1, 2 )

Symphysanodon disii Khalaf and Krupp, 2008:86 , figs. 1, 2; table I (original description, illustrations; holotype MSSA 64-20/ 1, 163 mm SL; type locality Gulf of Aqaba, Red Sea, off Aqaba, Jordan, ca. 150 m depth).

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 34 to 37. Lateral-line scales 48 to 50. Sum of total number of gillrakers plus lateral-line scales, in individual specimens, 82 to 87. Diameter of fleshy orbit 7.2 to 8.3 % SL. Depth of body 27.8 to 31.1 % SL. Length of pectoral fin 27.5 to 29.2 % SL. Length of anal-fin base 16.5 to 18. 0 % SL. Length of depressed anal-fin 31.1 to 34.9 % SL. Length of second anal spine 8.3 to 9.7 % SL. Head and body mostly red orange to rosy, caudal fin mainly rosy or purplish rose.

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. Branchiostegals 7. Dorsal-fin rays IX, 10. Anal-fin rays III, 7. Pectoral-fin rays 16* or 17.* Pelvic-fin rays I, 5. Caudalfin rays: principal 17 (9 + 8); branched 15 (8 + 7); procurrent 12 or 13* dorsally, 11 or 12* ventrally. Gillrakers on first arch 9 to 11* + 24 to 26* (total 34 to 37*). Tubed lateral-line scales ca. 48 to 50*. Sum of total number of gillrakers plus lateral-line scales, in individual specimens, 82 to 87*. 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. Uroneurals 2 pairs. Autogenous haemal spine associated with second preural centrum. Parhypural autogenous, bearing a hypurapophysis. Hypurals 1 and 2 fused, hypurals 3 and 4 fused; lines of fusion visible. Hypural 5 autogenous. Epurals 3. Epineurals associated with first 9 or 10* vertebrae. Pleural ribs on vertebrae 3 through 10. Trisegmental pterygiophores: 2 or 3* associated with dorsal fin, 3 with anal fin.

Snout relatively 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; lower jaw inclined dorsally with mouth closed; jaws about equal. Maxilla reaching posteriorly to a vertical well beyond middle of eye. Anterior and posterior nares fairly closely set on each side of snout. Pseudobranchiae present. Interorbital region flattened to slightly convex. Opercle with two flattened spines. Both limbs of preopercle usually without serrae, margins almost smooth; angle of preopercle without spine, but may be somewhat roughened, bifid spine-like process present on left side of one specimen, and enlarged serra just above angle on right side of holotype. 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 with scales. Branchiostegals and branchiostegal membranes without scales, gular region usually without scales. Dorsal and anal fins without scales (occasionally a few scales on some anal soft 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 well forked.

Premaxilla with outer series of small conical teeth and inner band of much smaller teeth; anteriorly, teeth in outer series considerably enlarged; premaxillary notch toothless. Dentary with band 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 conspicuously enlarged; many of enlarged teeth at anterior end of jaw exserted and fitting into premaxillary notch when mouth closed; symphysis toothless. Vomer and palatine with teeth; vomerine tooth patch small, chevron shaped or quadrangular, without posterior prolongation; palatine teeth in longitudinal band. Endopterygoid usually with teeth. Tongue with or without teeth. Four of the five specimens examined are males; they have the dentition much better developed than does the single female (see Fig. 2 ).

in percentages of standard length. Holotype: MSSA 64-20/1. Dam. = damaged;> = slightly damaged.

Character TAU P. TAU P. TAU P. TAU P. MSSA 13320 13321 13321 13320 64- 20/1 1 of 2 2 of 2 1 of 2 2 of 2

Standard length 146 148 157 159 163

Head, length 28.3 27.7 27.7 27.6 27.9

Head, depth 20.0 19.5 23.5 21.4 21.8 Coloration. Khalaf and Krupp (2008:87) described the coloration of the holotype of S. disii as: “Flanks of the freshly caught specimen... red, turning to a lighter pinkish ventrally and to dark orange-red dorsally; indistinct, broad, yellow-orange, longitudinal band from operculum to caudal peduncle (hardly visible); dorsal fin yellow, caudal fin reddish orange, with yellow hind-margin on upper lobe; anal, pectoral and pelvic rays light reddish, membranes transparent and without pigmentation.”

The color photograph of the freshly collected holotype in the original description ( Khalaf and Krupp, 2008:86, fig. 1) shows the head to be mainly red orange; body to be mostly red orange dorsally above faintly visible yellowish band running from opercle to about middle of caudal peduncle, rose in broad swath ventral to yellowish band; iris mainly orange to red orange with some blackish pigment anterodorsally; dorsal fin yellow, pectoral fin rosy, anal and pelvic fins rosy with transparent membranes, caudal fin mainly rosy overlain by yellowish on ventral bor- der of upper lobe. A color photograph of one of the TAU specimens ( Fig. 1 ; TAU P. 13320, 159 mm SL) shows it to have coloration similar to that of the holotype, differing in the iris being more yellow and the caudal fin almost entirely purplish rose with narrow yellowish borders along inner margins of both lobes.

TAU P. TAU P. TAU P. TAU P. MSSA

Character 13320 13321 13321 13320 64-20/1

1 of 2 2 of 2 1 of 2 2 of 2

Comparisons. Symphysanodon disii 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. Number of tubed lateral-line scales distinguishes S. disii (with 48–50) from the Indian Ocean species S. andersoni (with 60 or 61), total number of gillrakers on first gill arch separates S. disii (with 34–37) from S. andersoni (with 41 or 42) and the undescribed species from the Comoros (with 28), sum of total number of gillrakers plus lateral-line scales (in individual specimens) distinguishes S. disii (with 82 to 87) from S. xanthopterygion (with 94 to 101), number of pectoral-fin rays separates S. disii (with 16 or 17) from S. pitondelafournaisei (with 15), diameter of fleshy orbit differentiates S. disii (7.2–8.3 % SL) from the Pacific species S. typus (8.1–12.0 % SL), and length of second anal spine distinguishes S. disii (8.3–9.7 % SL) from the Pacific species S. katayamai (9.8–10.4 % SL). In addition, live coloration can be used to distinguish S. disii from the other species for which coloration is known, viz., S. berryi , S. katayamai , S. maunaloae , S. pitondelafournaisei , S. typus , and S. xanthopterygion .

Sexuality. Histological sections of the gonads of the five known specimens of S. disii show one ( TAU P. 13320, 146 mm SL) to be a mature female with evidence of recent spawning. The other four specimens are males: TAU P. 13320, 159 mm SL, spawning; TAU P. 13321, 157 mm SL, mature; TAU P. 13321, 148 mm SL (tissue badly degraded); holotype, 163 mm SL (tissue badly degraded). In the original description ( Khalaf and Krupp, 2008), the sex of the holotype was given as female.

Distribution. Symphysanodon disii is known only from the northern Gulf of Aqaba off Aqaba ( Jordan) and Eilat ( Israel).

Material examined. Five specimens, 146 to 163 mm SL.

Holotype: MSSA 64-20/ 1, 163 mm SL; Gulf of Aqaba, in front of phosphate port at Aqaba, Jordan (Aqaba is at 29°31’ N, 35°00’E); depth: ca. 150 meters; 0 5 October 1999; M. A. Khalaf.

Other material: Gulf of Aqaba off Eilat, Israel (Eilat is at 29°33’ N, 34°57’E); depth: 150 meters; 12 March 2008 — TAU P. 13320, two specimens, 146–159 mm SL; TAU P. 13321, two specimens, 148–157 mm SL.

Figures

FIGURE 1. Symphysanodon disii (TAU P. 13320, 159 mm SL), Gulf of Aqaba. Photographed by Avi Baranes.

FIGURE 2. Dentition on jaws of Symphysanodon disii. A. TAU P. 13320, 146 mm SL, female. B. TAU P. 13320, 159 mm SL, male. C. TAU P. 13321, 148 mm SL, male. D. Holotype, MSSA 64 - 20 / 1, 163 mm SL mm SL, male. E. TAU P. 13321, 157 mm SL, male. Digital photographs by Sean Money, computer enhanced by Albert E. Sanders (Charleston Museum).

Tables

TABLE 2. Miscellaneous data on Symphysanodon disii from the Gulf of Aqaba. Holotype: MSSA 64 - 20 / 1; for bilateral counts left side is presented first; GR + LL scales = sum of total number of gillrakers and tubed lateral-line scales; A = anal; D = dorsal; V = ventral; TMM = too many scales missing to make count.

Sex	female	male	male	male	male
Standard length (mm) Pectoral-fin rays	146 17, 17	148 17, 17	157 17, 17	159 17, 17	163 17, 16
Procurrent caudal-fin rays	D: 13, V: 12	D: 12, V: 12	D: 12, V: 11	D: 12, V: 11	D: 13, V: 12
Total 1st arch gillrakers	34	36	ca. 34	36	37
Lateral-line scales	49, 49	TMM	ca. 48, ca. 49	50, 50	50, 50
GR + LL scales	83	____	ca. 82, ca. 83	86	87
Trisegmental pterygiophores	D: 3, A: 3	D: 3, A: 3	D: 2, A: 3	D: 3, A: 3	D: 3, A: 3
Epineurals, pairs	9	10	10	10	10