Saurida tweddlei Russell, 2015, n.sp.

Saurida tweddlei n.sp.

New English name: Tweddle’s lizardfish Figures 1–3; Table 1.

Saurida undosquamis (non Richardson, 1848)— Amaoka et al. 1976: 115, Plate Sey-1 (Seychelles).

Holotype. SAIAB 185941 (tissue voucher ACEP 08-1710), 354.0 mm SL, Indian Ocean, Saya da Malha Bank, Mascarene Trawl Survey Station 19, 10.91°S, 60.97°E, 127 m, D. Tweddle and O. Alvheim, RV Dr Fridtjof Nansen, 7 July 2009.

Paratypes (11: 247.9–401.0 mm SL). MNHN 2012-0113, 355.3 mm SL, same data as holotype. NSMT- P 121334, 358.2 mm SL, station SKSK 7745, Indian Ocean, Saya da Malha Bank, 10°44’S, 61°04’E, FV Ryuyo- Maru No. 2, 6 December 1978. NSMT-P 121335, 327.4 mm SL, station SKSK 8512, Indian Ocean, Saya da Malha Bank, 10°36’S, 61°34’E, FV Ryuyo-Maru No. 2, 30 November 1978. NSMT-P 121336, 349.0 mm SL, SKSK 8513, same data as NSMT-P 121335. NSMT-P 121337, 365.0 mm SL, SKSK 8514, same data as NSMT-P 121335. NSMT- P 121338, 338.6 mm SL, SKSK 8515, same data as NSMT-P 121335. NSMT-P 121339, 352.0 mm SL, SKSK 8516, same data as NSMT-P 121335. NTM S.17300-001, 345.3 mm SL, same data as holotype. SAIAB 84181, 3: 247.9– 401.0 mm SL, same data as holotype.

Diagnosis. A large species of Saurida, with the following combination of characters: dorsal fin with 12–13 rays; pectoral fins with 14–15 rays; lateral-line scales 53–55; transverse scale rows above lateral line 4½, below lateral line 5½; pectoral fins moderately long (extending to or just beyond a line from origin of pelvic fins to origin of dorsal fin); 2 rows of teeth on outer palatines; 0–3 teeth on vomer; tongue with about 4–5 rows of teeth posteriorly; caudal peduncle compressed (depth greater than width); stomach and intestine pale whitish.

Description. Counts and proportional measurements of the type series are provided in Table 1. Dorsal-fin rays 13 (12–13); pectoral-fin rays 14 (14–15); pelvic-fin rays 9; anal-fin rays 11 (10–12). Pored lateral-line scales 54 (53–55); transverse scale rows above lateral-line 4½, transverse scale rows below lateral-line 5½; scale rows below lateral line with melanophores 2 (1–2); pre-dorsal scales 19 (16–20); pre-adipose scales 16 (15–18); post-adipose scales 10 (11–12). Vertebrae 49–50.

Body elongate and cylindrical, somewhat depressed on head and compressed on caudal peduncle, the latter with slightly raised lateral line scales, forming a slight ridge; scales large, cycloid, not very deciduous; scales present on cheek and opercle. Snout rounded when viewed from above. Nostrils located about midway between snout tip and anterior margin of orbit; anterior nostrils a little larger than posterior, anterior one with a broad dermal flap posteriorly. Eye circular, directed laterally, covered with fleshy adipose eyelid anteriorly and posteriorly. Interorbital region broad, slightly concave.

Mouth very large, the gape extending well beyond posterior margin of eye. Teeth on jaws numerous, small, canine-like, generally in four rows, outermost teeth smallest, innermost longest, visible when mouth closed; similar teeth on the palate, tongue and branchial arches; palatine teeth in two separate series, teeth of outer series long, in two rows, with anterior teeth longer, teeth of inner series short, in about six poorly defined rows; outer palatine series converge anteriorly but separated by vomer which is toothless or bears 1–3 teeth; tongue short, spatulate, fleshy, with triangular shaped patch of teeth, in about 4 (4–5) rows posteriorly; lower jaw slightly shorter than upper jaw and fits into groove between teeth at tip of upper jaw; gill rakers absent, branchial arches each with about 4 rows of teeth, those on the inside largest.

Origin of dorsal fin just posterior to midpoint of distance from snout to adipose-fin origin; base of dorsal fin longer than that of anal fin; adipose fin above posterior half of anal fin; anus just anterior to origin of anal fin; pectoral fins moderately long, 13.0% (12.6–17.4%) of SL, tip of pectoral fin reaching to or just beyond a line from base of pelvic fin to origin of dorsal fin (P-D line); pectoral and pelvic fins with long and pointed axillary scales, those of pelvic a little shorter; caudal fin deeply forked, upper and lower lobes about equal.

Peritoneum pale whitish; stomach pale (slightly greyish anteriorly in a few specimens), intestine pale whitish.

Colour in alcohol. Brown on back, paler below lateral line, pigment extending to about 2 (1–2) scale rows below lateral line; pectoral fins dusky over outer two-thirds of fin; pelvic fins pale; dorsal, caudal and anal fins pale, anterior margin and posterior edge of dorsal and caudal fins dusky; leading edge of caudal fin with 10 (8–16) blackish spots; adipose fin pale or dusky over much of fin or along outer margin.

Colour of fresh specimens (Fig. 2, 3). Top of head and back dark brown or coppery brown, some scales narrowly edged with black, forming a variegated pattern; silvery white below lateral line; leading edge and outer margin of dorsal fin light dusky; adipose fin light dusky over most of fin; leading edge of caudal fin with 8–16 blackish spots, posterior edge and lower lobe of caudal fin dusky; pectoral fins dusky, base of fin translucent; pelvic fins pale lemon at base, rest of fin translucent; anal fin translucent.

Distribution and abundance. Saurida tweddlei n.sp. is so far known only from the northern part of the Mascarene Plateau in the Indian Ocean, from Seychelles Bank and Saya de Malha Bank (Fig. 1). The typespecimens collected by RV Dr Fridtjof Nansen at station 19 were trawled in depths of 127 m, but the species was also caught at other stations (Fig. 1) in depths ranging from 57– 76 m. This species was one of the most abundant trawl species on the northern Mascarene Plateau, comprising 22.5–61.2% (mean 36%, n = 3) of the total catch weight on the Saya de Malha Bank, and 0.5–41.4% (mean 18.8%, n = 6) of the total catch weight on the Seychelles Bank (D. Tweddle, unpublished data).

Etymology. Named in honour of Denis Tweddle, Honorary Research Associate at SAIAB, who collected this species during an exploratory fishing survey of the Mascarene Plateau by the RV Dr Fridtjof Nansen, and who brought it to the attention of the author during a visit to SAIAB. The common English name Tweddle’s lizardfish is proposed for this species.

Comparison. This species was previously reported from the Seychelles by Amaoka et al. (1976: p.115, Plate Sey-1) misidentified as Saurida undosquamis (Richardson). Although the specimen could not be located in the NSMT and is presumed lost, the photograph (Fig. 3) is clearly identifiable as S. tweddlei n.sp.

Inoue & Nakabo (2006), in a review of the Saurida undosquamis group, showed the name S. undosquamis (type-locality north-western Australia) has been applied to a complex of species distributed widely throughout the Indo-West Pacific. They recognised four species in the group (S. undosquamis; S. umeyoshii Inoue & Nakabo, 2006; S. macrolepis Tanaka, 1917; and S. longimanus Norman, 1939). Saurida macrolepis (type-locality Japan), formerly synonymised with S. undosquamis by Norman (1935), was recognised as distinct by Inoue & Nakabo (2006), who applied the name to the species previously recorded as S. undosquamis in the Western Indian Ocean. Inoue & Nakabo (2006) considered S. macrolepis to be a wide-ranging, geographically variable species, occurring in the Western Pacific from southern Japan to Australia, and in the Indian Ocean westwards to East Africa, the Red Sea and Persian Gulf. However, examination of specimens from the Red Sea-Mediterranean shows they are morphologically and genetically distinct from S. macrolepis from Japan, and represent a new species (Russell et al. in press). Saurida undosquamis sensu Inoue & Nakabo (2006) also appears to comprise more than one species, and is the subject of ongoing study by the author.

Saurida tweddlei n.sp. differs from the species in the Red Sea-Mediterranean misidentified as S. undosquamis and S. macrolepis, most notably in having a greater number of lateral line scales (53–55 versus 47–51 in S. sp) and vertebrae (49–50 versus 44–47 in S. sp). It also differs from S. undosquamis sensu stricto in having longer pectoral fins (extending to well beyond P-D line, versus pectoral fins shorter, not reaching beyond P-D line in S. undosquamis); lateral line scales 53–55 (versus 54–58 in S. undosquamis); teeth on tongue moderately large, in about 4–5 rows (versus teeth on tongue small, in about 7–12 rows in S. undosquamis); and 8–16 (usually 11–14) blackish spots on leading edge of caudal fin (versus 5–12 spots in S. undosquamis).

Saurida tweddlei n.sp. is distinguished from other Western Indian Ocean species of Saurida in the key below.