Arctozenus risso ( Bonaparte, 1840 ), 1987

Ho, Hsuan-Ching & Duhamel, Guy, 2019, A new species of the fish genus Arctozenus from the Kerguelen Islands, with comments on the lost teeth in adults (Aulopiformes: Paralepididae), Zootaxa 4651 (3), pp. 497-512 : 499-503

Arctozenus risso ( Bonaparte, 1840)

English name: Spotted barracudina

Figs 1A–C , 2A,B , 3A,B , 5A,B ; Table 1

Paralepis isso Bonaparte, 1840 : pl. 124, fig. 2 (No types known; neotype designated herein).

Paralepis kroyeri Lütken, 1892:228 (No types known; neotype designated herein).

Paralepis coruscans Jordan & Gilbert, 1881:411 (Type locality: Port Townsend harbor, Washington, U.S.A.).

Designation of neotype. According to Post (1972), there is no type for Paralepis risso Bonaparte, 1840 or Paralepis borealis Krøyer in Gaimard (1847) . A neotype is designated for both in order to stabilize the diagnosis of the species, according to Article 75.3 of The International Code of Zoological Nomenclature ( ICZN, online version).

Neotype. MNHN 2018-0264 (266 mm SL), out of MNHN 2000-5431 , “Thalassa” station b229, 62°16’58.8”N, 10°10’1.2”W, off Faroe Islands, North Atlantic Ocean , 676–696 m, 11 May 1975; also designated as neotype of Paralepis borealis Krøyer in Gaimard, 1847 .

Non-types. All from Atlantic Ocean. MNHN 2000-5429 (3, 256–258) “ Thalassa ” station b570fq109, and MNHN 2000-5430 (4, twisted), 46°51’00”N, 59°37’1.2”W, 384–384, 28 Jul. 1975 . MNHN 2000-5431 (27, 212– 280), “ Thalassa ”, station b229, collected with neotype . MNHN 2000-5432 (26, 191–250), “Thalassa”, station b230, 62°25’1.2”N, 9°33’00”W, 566–588 m, 12 May 1975 . MNHN 2000-5433 (2, 226–236), “Thalassa”, station b328fq67, 50°37’1.2”N, 53°33’00”W, 311–312 m, 20 Jul. 1975 . MNHN 2000-5434 (1, 261), “Thalassa”, station b346fq85, 49°28’1.2”N, 50°12’00”W, 320–322 m, 22 Jul. 1975 . MNHN 2000-5435 (1, 235), “Thalassa”, station b344fq83, 49° 3 4’1.2”N, 50°16’1.2”W, 336–382 m, 22 Jul. 1975 . MNHN 2000-5436 (1, 253), “Thalassa”, station b322fq61, 53°9’00”N, 51°58’58.8”W, 940 m, 17 Jul. 1975 . MNHN 2000-5437 (1, 267), “Thalassa”, station b228, 62°43’1.2”N, 9°39’00”W, 494–502 m, 11 May 1975 . MNHN uncat. (1, 199, photo only), tissue no. BPS-1960, 45°56’N, 4°16’, Bay of Biscay , France, northeast Atlantic Ocean, 20 Oct. 2011 .

Diagnosis. Body uniformly and densely covered with chromatophores; body depth 9–16 times in SL, a short, deep head, depth at middle of eye 3.5–4.1 in HL, VFO under dorsal-fin base, and anterior lateral-line scales subequal in depth and length.

Description. Following data is for neotype with of non-types (n = 54) in parentheses, except where otherwise indicated.

Dorsal-fin rays 9 (9–10, usually 9); pectoral-fin rays 13 (13–14, usually 13); pelvic-fin rays 9 (9–10, usually 9); anal-fin rays 31 (30–33). Vertebrae (n=15): prehaemal 39 (39–41), caudal 46 (43–46), predorsal 37 (37–39), prepelvic 40 (40–43), preanal 54 (52–56), and total 85 (83–87). Gill rakers 8 (7–10) on upper limb, 27 (28–31) on lower limb, 11 (11–13) on ceratobranchial, 16 (14–18) on hypobranchial. Lateral-line scales: predorsal 38 (37–39), prepelvic 40 (40–42), preanal 53 (52–55), total 66 (65–70).

Body elongate and compressed in individual smaller than 250 mm SL, becoming stouter and thicker in specimens more than 250 mm SL, greatest depth 11.2 in SL (9.5–13.0 in specimens> 250 mm SL; 12.9–15.8 in specimens <250 mm). Caudal peduncle subequal to eye diameter. Posterior half of abdomen with slightly developed flap. Ventral adipose fin absent.

Head moderately long, pointed ( Fig. 2A ), its length 4.9 (4.6–5.0) in SL, its depth slightly (<250 mm SL) to much lower (> 250 mm SL) than the trunk. Mouth terminal, slender, its gape extends to about one eye diameter in front of the eye; lower jaw not upturned at tip, its tips bearing a black non-ossified tissue. Eye large, bony diameter 5.9 (5.4–6.6) in HL. First suborbital bone slightly expanded anteriorly, second long, about twice the third, third to fifth stout, the sixth well expanded dorsally. Interorbital space narrow and flat, its width 8.5 (8.5–9.8) in HL. Two ridges on each side of interorbital space, the inner one extended forward to tip of snout. Premaxilla rectangular, closely attached to maxilla; maxilla extending to slightly, but clearly, less than one eye diameter in front of the eye. Two nostrils closed together, above tip of maxilla or slightly behind. Opercle with low ridges forming radiated pattern (when skin removed), posterior margin slightly indented. Tongue surrounded by narrow fleshy membrane.

DFO at about posterior third of standard length, predorsal length 1.5 (1.5–1.6) SL. Pectoral fin above ventral margin, about lower level of gill cover, the uppermost ray at about same level of lower margin of eye. VFO below posterior half of dorsal-fin base, never behind that, pre-pelvic length 1.4 (1.4–1.5) in SL. Anal fin originating at posterior sixth of standard length, pre-anal fin length 1.2 (1.2) in SL. Anal fin base short, 7.2 (6.7–7.2) in SL. Dorsal adipose fin over posterior end of anal-fin, about 1.5 its base length before caudal-fin base, its base length less than eye diameter.

Two to four small fangs at front of upper jaw, followed by a closet row of tiny blade-like teeth along maxilla. Vomerine teeth absent. Two rows of fangs on anterior palatines, in 5 or 6 (5–8) widely-spaced pairs, those in outer row fixed and much smaller than those in inner row, which are depressible, the third or fourth especially enlarged, followed by single row of small fangs posteriorly. Two or three small fangs at front of lower jaws, followed by a short row of small teeth, then two rows of fangs posteriorly, forming 14 (10–14) widely-spaced pairs, those in outer row fixed and smaller than those in inner row which are depressible. About 2 irregular rows of small teeth on each side of outer portion of tongue.

Gill rakers as described by Post (1987, figs. 1c, d), present on most gill arches, shield-shaped, each with three or four rows of small teeth.Pharyngeal teeth from short, slender, forming two long patches, anterior patch long triangular with 3 irregular rows; posterior patch oval with up to 6 rows. About 10 scattered teeth on fifth ceratobranchial, in one irregular row. Gill filaments present on the first to fourth arches, absent on fifth. Anterior half of fifth gill arch connected to the forth by membrane. Pseudobranch present, in a shallow chamber above first gill arch.

Body completely scaled, mostly lost leaving distinct pockets. Lateral-line scales originating from above pectoral girdle and running along upper third of the flank to above about over middle of anal-fin base. Anterior lateral-line scales about twice as long as its height, gradually becoming smaller and narrower posteriorly, but not to the degree as in members of Lestrolepinae; two large pores on posterior margin of each scale. Luminous organs absent.

Coloration ( Figs. 1B,C , 2A,B , 3A,B ). Preserved specimen with body generally blackish, densely covered with fine chromatophores; some much larger spots on dorsum and posterior half of body visible without magnification; dorsal surface of head and snout blackish; tips of jaws black. Gill chamber entirely blackish; mouth cavity mostly pale with irregular patches of fine chromatophores. Peritoneum black. All fins hyaline, except for pigmented upper rays of pectoral fin.

Distribution. Circumglobal in temperate and tropical seas including the Arctic ( Post, 1987), but probably not present in the Southern Ocean (see below).

Remarks. The world distribution of this species is as provided by Post (1987) with one exception. In his list of specimens, one lot (WH247, 61°10’S, 56°07’W, 180 mm SL) was collected from Antarctic region (also see Post, 1987: fig. 2). We are not sure whether he measured this specimen so we could not judge this record. Post (1990) also recorded A. risso occurring in the Southern Ocean for which he recorded the body depth 5.9–7.7% SL and head length 21.8–27.5% SL which did not correspond with his previous data ( Post, 1987: table 1). We believe this specimen to be the new species described below. Post (1987) divided the body depth of A. risso 8.0–11.5% SL (30°S) or 8.5–11.7% SL (30°N) which is similar to our specimens with body size more than 250 mm SL (7.7–10.6% SL, n = 18), but not these smaller than 250 mm SL (6.3–7.7%, n = 36). The presence of A. risso in Antarctic is doubtful.

Figures

FIGURE 1. A–C. Arctozenus risso (Bonaparte, 1840).A. Original drawing which Paralepis risso Bonaparte, 1840, reproduced from Cuvier in Cuvier & Valenciennes, 1829: pl. fig. 66). B. Neotype of Paralepis risso Bonaparte, 1840, MNHN 2018-0246. C. MNHN uncat. (tissue no. BPS-1960), 199 mm SL, photo by Samuel Iglésias. D–E. Arctozenus australis sp. nov. D. Holotype, MNHN 2000-0260. E. Fresh condition, one of paratypes.

FIGURE 2. Comparison of head and relative position of DFO and VFO of A. risso and A. australis. A-B. Neotype of A. risso. C. Paratype of A. australis, MNHN 1992-1218. D. Holotype of A. australis. Bars indicate end of dorsal-fin base (upper) and origin of pelvic fin (below).

FIGURE 3. Microscopy photographs of anterior trunk region (A, C) and close-up of above lateral line at same region (B, D). A–B. Neotype of A. risso. C–D. Holotype of A. australis. Both with complete skin, but most scales lost.

FIGURE 5. Comparison between two Arctozenus species.A. Body depth versus standard length; upper plots are original values (mm) and lower plots are % SL of specimens. B. Ratio of snout length/eye diameter versus standard length.