Careproctus cyanogladius Kai, Endo & Nakayama 2021, sp. nov.

Careproctus cyanogladius Kai, Endo & Nakayama sp. nov.

New Japanese name: Tsurugi-kon’nyaku-uo

Figs. 1A, 1B, 2A, 2D, 3A; Table 1

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Holotype. BSKU 96466, 303.6 mm SL, male, 38.4647ºN, 143.5283ºE, off Kinkazan, Miyagi, Japan, 3,137–3,223 m depth (KT08-27, St. K-3), R / V Tansei-maru, 23 Oct. 2008, coll. by Hiromitsu Endo and Naohide Nakayama.

Paratypes. BSKU 96458, 161.9 mm SL, male, 39.5342ºN, 143.6835ºE, off Miyako, Iwate, Japan, 3,150–3,201 m depth (KT08-27, St. M-4), R / V Tansei-maru, 22 Oct. 2008, coll. by Hiromitsu Endo and Naohide Nakayama; BSKU 96474, 203.0 mm SL, female, 38.4748ºN, 143.3470ºE, off Kinkazan, Miyagi, Japan, 2,698–2,814 m depth (KT08-27, St. K-3), R / V Tansei-maru, 23 Oct. 2008, coll. by Hiromitsu Endo and Naohide Nakayama.

Diagnosis. A species of Careproctus with the following combination of characters: vertebrae 63; dorsal-fin rays 57–58; anal-fin rays 50; principal caudal rays 7; pectoral-fin rays 29–31; pectoral fin without notch; uppermost pectoral-fin base below a horizontal through posterior margin of maxillary; pelvic disk oval; cephalic pores 2-6-7-?, chin pores well separated; teeth simple; pyloric caeca 6–10; anus anterior to middle point between posterior rim of pelvic disk and anal-fin origin, slightly closer to pelvic disk than to anal-fin origin; body color pale blue or gray when fresh.

Description. Counts and measurements are shown in Table 1. Paratype data are given in parentheses if different from the holotype.

Body slender, compressed, tapering posteriorly, deepest at anus (Fig. 1A, B). Skin thin, fragile, lacking prickles. Head compressed, dorsal profile steep from nape to snout. Snout deep, rounded, slightly projecting anterior to lower jaw. Mouth large, subterminal; maxilla extending to posterior rim of orbit; oral cleft extending to anterior rim of orbit. Premaxillary teeth simple, canine (Fig. 2A), in 7 (6–10) oblique rows. Mandibular teeth simple, canine, in 5 (6–7) oblique rows; inner teeth larger. Diastema absent at symphysis of upper and lower jaws. Orbit rounded, relatively small. Nostril single, with short tube slightly below level of mid-orbit. Cephalic sensory pores small: nasal pores 2, maxillary pores 6, preoperculomandibular pores 7, suprabranchial pores damaged in holotype and all paratypes; cephalic pore pattern 2-6-7-?. Chin pores paired, opening well separately (Fig. 3A). Upper margin of gill slit at level with middle of orbit, lower margin broken in holotype and all paratypes. Gill rakers 11 (10), short. Opercular flap broad, square. Pyloric caeca 10 (6), on center-left side of visceral cavity.

Vertebrae 63 (11+52). Pleural ribs on abdominal vertebrae 9 and 10 (or 8 and 9). Dorsal-fin rays 58 (57), gradually increasing in height posteriorly. Anteriormost dorsal-fin pterygiophore without ray, inserted between 3 rd and 4 th neural spines; dorsal-fin origin above anus. Anal-fin rays 50, gradually increasing in height posteriorly; anal-fin origin below 9 th dorsal-fin ray. One anal-fin pterygiophore anterior to first haemal spine bearing a single ray (no anal-fin pterygiophore anterior to first haemal spine in paratypes). Membrane of posterior dorsal- and anal-fin rays attached about equidistant on caudal fin. Caudal fin truncate (damaged in holotype). Principal caudal-fin rays 7 (upper 3 and lower 4 in all specimens), single dorsal and anal procurrent rays present. Hypural plates fused with terminal vertebral centrum, slit absent.

Pectoral fin rounded, with 31 (29–30) rays, 2 nd ray from uppermost longest, just reaching to anal-fin origin (to 2 nd or 3 rd anal-fin ray); rays of lower lobe exserted, tip of longest ray one-third free of membrane; notch absent; uppermost pectoral-fin base below a horizontal through posterior margin of maxillary (Fig. 1A, B); symphysis of pectoral fins below anterior rim of orbit. Pectoral-fin base concave between 20 th and 21 st (21 st and 22 nd or 22 nd and 23 rd) rays from uppermost. Proximal pectoral radials 4, relatively small and rounded, equally spaced (Fig. 2D). No interradial fenestrae between proximal radials. Scapula broad with robust helve. Coracoid rounded dorsally with short thin helve. Distal radials present at base of all pectoral-fin rays, except for uppermost and lowermost rays. Pelvic disk oval, length 1.5 (1.5–1.8) times longer than its width. Anus anterior to middle point between posterior rim of pelvic disk and anal-fin origin, slightly closer to pelvic disk than to anal-fin origin.

Coloration: Head and body pale blue or gray with dark peritoneum visible through thin skin when fresh (Fig. 1B). Dorsal, anal and pectoral fins pale blue; edges of posterior dorsal and anal fins dark brown; pectoral fin dark brown. Eye black. Body uniformly gray when preserved, and fins pale. Distal margins of dorsal and anal fins dark brown; pectoral fin dark brown. Peritoneum and orobranchial cavity dark brown; stomach and pyloric caeca white.

Distribution. Western Pacific Ocean, off the Pacific coast of Tohoku District, northern Honshu Is., Japan, in depths of 2,698 –3,223 m.

Etymology. The specific name “ cyanogladius ” derived from Latin “cyaneus” (blue) and “gladius” (sword), refers to the pale blue coloration and the compressed and elongated sword-like body shape.

Remarks. Careproctus cyanogladius sp. nov. is most similar to Careproctus gelatinosus (Pallas, 1769), which was redescribed as valid by Chernova (2005) who considered it a senior synonym of Careproctus furcellus Gilbert & Burke, 1912, in having simple teeth, a pectoral fin without a notch, chin pores well separated, and the uppermost pectoral-fin base below a horizontal through the posterior margin of the maxillary (Kido 1988; Chernova 2005). However, C. cyanogladius sp. nov. has fewer vertebrae (63 vs. 67–71), dorsal- (57–58 vs. 61–65) and anal-fin rays (50 vs. 54–59), and pyloric caeca (6–10 vs. 29–49) (Kido 1988; Chernova 2005; this study). The anus of C. cyanogladius sp. nov. is slightly anterior to the middle point between the posterior rim of the pelvic disk and the anal-fin origin, but that of C. gelatinosus is just behind the posterior rim of the pelvic disk. In addition, the fresh coloration readily distinguishes the two species: C. cyanogladius sp. nov. has a pale blue body with dark peritoneum visible through thin skin; C. gelatinosus has a typically pale pink body (Kido 1985; this study) (Fig. 4).

Careproctus laperousei Chernova, Thiel & Eidus, 2020 is only known from the holotype collected from the northern slope of Kuril-Kamchatka Trench at depth of 4,796 –4,803 m. It is also similar to the present new species in having simple teeth, a pectoral fin without a notch, and chin pores in separated pits (Chernova et al. 2020). The count of pectoral-fin rays in C. laperousei (26) is near the lower end of the range of C. cyanogladius sp. nov. (29–31), but the counts of dorsal- and anal-fin rays and vertebrae of the former are different from the latter (53 vs. 57–58, 45 vs. 50, and 57 vs. 63, respectively). Careproctus laperousei can also be distinguished from the new species by several other characters, including the position of the pectoral fin (uppermost pectoral-fin base at the level of maxillary pores of infraorbital region) and the anteriormost dorsal-fin pterygiophore with a ray (Chernova et al. 2020).

Among species of Careproctus known from the North Pacific, C. cyanogladius sp. nov. shares a gray or dark body coloration and simple teeth with Careproctus bathycoetus Gilbert & Burke, 1912, Careproctus cypselurus (Jordan & Gilbert in Jordan & Evermann, 1898), Careproctus homopterus Gilbert & Burke, 1912, and Careproctus nigricans Schmidt, 1950. However, the new species can be readily distinguished from C. bathycoetes by having more pectoral-fin rays (29–31 vs. 22), from C. cypselurus by having a truncated caudal fin (vs. deeply forked), and C. nigricans by the anus position (slightly anterior to the middle point between the posterior rim of the pelvic disk and the anal-fin origin vs. just behind the posterior rim of the pelvic disk) and fewer principal caudal-fin rays (7 vs. 8–10) (Jordan & Evermann 1898; Gilbert & Burke 1912; Schmidt 1950; this study). Gilbert & Burke (1912) described C. homopterus, but apparently were mistaken in describing the holotype as having 32 pectoral-fin rays. The holotype has 21 pectoral-fin rays with a distinct notch, being clearly different from C. cyanogladius sp. nov. (29–31 pectoral-fin rays without a notch).