Hymenocephalus fuscus Mcmillan & Iwamoto, 2014, sp. n.

Hymenocephalus fuscus sp. n.

Black membranehead

(Figures 1–3; Table 1)

Hymenocephalus spp. (in part): Paulin et al. 1989: 124, 255 (in key and listed). Hymenocephalus sp.: King et al. 2009: 531 (listed).

Diagnosis. Pelvic fin rays 11–12, gill rakers first arch (outer/inner) 12–15/16–19, barbel absent or minute, orbit diameter 20–33 % HL, body depth 70–85 % HL, suborbital width 23–28 % HL, snout length 25–33 % HL, upper jaw length 38–48 % HL. Head and trunk of fresh specimens blackish, tail brownish peppered with melanophores. Body and tail with large, oval, deciduous scales.

Specimens examined. Holotype. CSIRO H 6181-01 (29 mm HL, 133+ mm TL), Tasman Sea, Wanganella Bank, 30º 15' S, 167º 23' E to 30º 15' S, 167º 24' E, 850 m, 15 May 1999, Saxon Onward, station SO/9902/2.

Paratypes (9: 10.6–28 mm HL, 48–148 mm TL ). CSIRO H 6181-03 (28 mm HL, 127+ mm TL), same data as holotype. NMNZ P. 0 0 2270 (10.6 mm HL, 48+ mm TL), New Zealand, Bay of Plenty, North Island, 37º 29' S, 177º 17' E, 549 m, collected by Dell, Castle, Garrick, & Moreland, station DM 204, otter trawl, 25 Feb 1957. NMNZ P. 0 13087 (12 mm HL, 70+ mm TL), New Zealand, Moa Seamount, North Island, 35º 15' S, 167º 14' E, unknown depth, RNZFA Tui, AUZ 0 67, 22 Jul 1962. NMNZ P. 0 23470 (17 mm HL, 57+ mm TL) & NMNZ P. 0 23473 (22.1 mm HL, 104+ mm TL), New Zealand, northwest of Three Kings Islands, 33º 55.1' S, 171º 55.05' E, 985–1003 m, RV James Cook, JCO8106/052, bottom trawl, 23 Apr 1981. NMNZ P. 0 23472 (25 mm HL, 117+ mm TL), northwest Challenger Plateau, outside New Zealand EEZ, 37º 29.6' S, 167º 47.4' E to 37º 29.4' S 167º 45.4' E, 880–884 m, RV James Cook, station JCO8102/021, bottom trawl, 26 Jan 1981. NMNZ P. 0 39538 (2: 26–27.4 mm HL, 86+–148+ mm TL) & NMNZ P. 0 39546, (24.2 mm HL, 92+ mm TL), West Norfolk Ridge, New Zealand EEZ, 34º 15' S, 168º 22' E, 1195–1202 m, RV Tangaroa, NORFANZ TAN0308/146, wing trawl, 0 3 Jun 2003.

Description (Counts and proportional measurements are presented in Table 1). Head bones thin, delicate, forming large plate-like projections dorsally, and around snout and orbit. Head covering probably membranous, easily damaged. Suborbital ridge very broad. Snout protruding slightly beyond mouth (but snout easily damaged). Orbits small but surrounding bony skeleton delicate, easily damaged. Upper jaw extending posteriorly to about rear edge of orbit. Teeth in both jaws small, sharply pointed, a band of up to 5 rows deep in upper jaw and narrow band of about 2 rows in lower jaw. Chin barbel absent or minute. Origin of dorsal and pectoral fins about on same vertical but pelvic fin base slightly anterior to pectoral fin base. First dorsal fin height less than HL, about equal to post-rostral length and pectoral fin length. Pectoral and pelvic fins with long delicate filaments. Interspace between first and second dorsal fins short, about same or slightly longer than the length of the first dorsal fin base. Longest second dorsal fin rays (posteriorly) about half orbit diameter. Longest anal fin rays about two-thirds orbit diameter. Light organ ventral striae tissue obvious on isthmus, and on trunk above pelvic fin bases. One small oval lens of light organ anterior to pelvic fin bases and a second lens before anus. Large deciduous scales on body, larger on trunk, about 8 scales in diagonal row (angled posterior-ventrally) from first dorsal fin origin to anal fin. Scales on head (observed where skin intact) including ventral surface of lower jaw.

Colour. Head including lower jaw and trunk below pectoral fin blackish. Nape, trunk dorsally, and tail brownish, peppered with melanophores with darker margins of scale pockets. All fins blackish. Roof of mouth greyish, tongue whitish, floor of mouth greyish with two paler longitudinal streaks below tongue on each side of mid-line. Branchial cavity blackish.

Size. To about 29 mm HL and 148 mm TL.

Distribution (Figure 3). Known from the Wanganella Bank, West Norfolk Ridge, off northeast and north coasts of North Island, and northwest Challenger Plateau.

Etymology. From the Latin fuscus, meaning swarthy, in reference to the overall dark colouration.

Comparisons and remarks (Table 1). We were reluctant to describe this species as new because initially we only knew of eight badly damaged specimens, but the discovery of two well preserved CSIRO specimens (designated here as the holotype and a paratype) enabled us to confirm our recognition of the new species. The lower gill raker counts (first and second arches, lateral and medial series) are important differences between the new species and the other similar species in the Hymenocephalus aterrimus species group listed below. These species share features including a large head with a high mesial extension of the nasal bones that are very soft and often damaged, small or rudimentary barbel, and dark brown or black head and body. Hymenocephalus aterrimus Gilbert 1905 was described from Hawaii but was also recorded from the tropical western North Atlantic Ocean, Indian Ocean, New Caledonia region, and off New South Wales Australia, at 340–1463 m (Iwamoto & Merrett 1997, Iwamoto & Graham 2001). It was also recorded with some uncertainty by Sazonov & Iwamoto (1992) from the Sala-y-Gomez and Nazca Ridges. It is a darkly pigmented species with a relatively large and deep head, prominent but soft median bony ridge dorsally on the snout, small orbits, and no chin barbel. It has more pelvic fin rays (13–14), more inner (mesial) gill rakers on the first (20–25) and second (21–26) arches, a larger mouth with upper jaw 45–56% HL, and narrower suborbital ridge (17–23% HL) than H. fuscus. New Caledonian specimens identified as Hymenocephalus cf. aterrimus also had more gill rakers and a larger mouth, with longer upper jaw compared to H. fuscus. Hymenocephalus barbatulus Gilbert & Hubbs 1920, described from the Philippines, has 7 pelvic rays, and H. papyraceus Jordan & Gilbert 1904, described from Japan, has a distinct chin barbel.