Hymenogadus gracilis Gilbert & Hubbs 1920

Hymenogadus gracilis (Gilbert & Hubbs 1920)

Slender membranehead

(Figures 3, 9, 10; Table 4)

Hymenocephalus gracilis Gilbert & Hubbs 1920: 522, Fig. 31 (Holotype: USNM 78227, off southern Luzon Island, Philippines, 13° 28'45" N, 121° 01'12" E, Albatross station 5292, depth 162 fathoms [296 m]). Hymenogadus gracilis: Okamura, 1970: 61 (Japan). Chiou et al., 2004: 44 –45 (Taiwan). Iwamoto et al. 2011: 528 (status of genus).

Hymenocephalus (Hymenogadus) gracilis: Iwamoto, 1990: 230 (listed). Pequeño 1997: 82 (listed). Iwamoto & Merrett, 1997: 518 (New Caledonia region). Iwamoto, 1999: 1991 (listed). Bray et al. 2006: 595.

Diagnosis. Spinous first dorsal fin ray weakly serrated, more obvious near tip of ray; pelvic fin rays 7–10, usually 8–9; gill rakers first arch (outer/inner) 8–12/14–18; barbel large, length 20–30% HL; snout length short 16–26% HL; suborbital very narrow 4–8% HL; upper jaw length 43–52% HL; one row of enlarged melanophores along lateral mid-line of the tail; body cylindrical. A small species to 130 mm TL.

Specimens examined (5, New Zealand only). NMNZ P. 0 34500 (20.9 mm HL, 101+ mm TL), off Cavalli Islands, 34º 47.8' S, 174º 6.4' E, 436 m, NZOI station I0365, 10 Nov 1977. NMNZ P. 0 34517 (13 mm HL, 73 mm TL), east of Parengarenga Harbour, 34º 32.2' S, 173º 38' E, NZOI I0348, 0 7 Nov 1977. NMNZ P. 0 38949 (12 mm HL, 63+ mm TL), Reinga Ridge, New Zealand EEZ, 34º 9.9' S, 171º 27' E, 558–573 m, RV Tangaroa, NORFANZ TAN0308/008, Sherman sled, 12 May 2003. NMNZ P. 0 39445 (15.5 mm HL, 74+ mm TL), Reinga Ridge, New Zealand EEZ, 33º 23.6' S, 170º 12.3' E, 465–490 m, RV Tangaroa, rough bottom trawl, 0 1 Jun 2003. NMNZ P. 0 54889 (17.1 mm HL, 93 mm TL), Rumble V, 36º 8.4' S, 178º 11.6' E, 380–480 m, 27 Oct 2012.

Non-New Zealand specimens examined. Holotype: USNM 78227 (19.4 mm HL, 93+ mm TL), off southern Luzon Island, Philippines, 13° 28'45" N, 121° 01'12" E, depth 162 fathoms (296 m), Albatross station 5292, 23 Jul 1907. BSKU M7520 (19.3 mm HL, 112 mm TL), BSKU M7513 (23 mm HL, 127 mm TL), BSKU M7514 (19 mm HL, 88 mm TL), BSKU M7523 (21.9 mm HL, 122 mm TL), BSKU M7521 (19 mm HL, 103 mm TL), off Shikoku Island, east coast of Japan. BSKU 34509, (22.1 mm HL, 121 mm TL), Shikoku Island, Kochi City, Mimase Fish Market. BSKU 1825 (21.2 mm HL, 108 mm TL), BSKU 1823, (18 mm HL, 98 mm TL), Shikoku Island, Kochi City, Mimase Fish Market, 1 September 1951. CAS 228291 (2) (20.7–22 mm HL, 112+–113+ mm TL), Shikoku Island, Kochi City, Mimase Fish Market, N. Nakayama, 6 Apr 2008. CAS 50166 (3) (16–18.5 mm HL, 60+– 93 mm TL), Zanzibar, 6?48' S, 39?51' E, 400– 300 m, Anton Bruun cruise 9, station 425, 20 Nov1964.

Counts and measurements (Table 4).

Description (Counts and proportional measurements are present in Table 4).

Colour. Head mostly pale but blackish along dorsal margin of snout, interobital region, lips, ventral edge of suborbital shelf, and ventral parts of preopercle. Mouth, including tongue, and branchial cavity pale. Barbel pale or transparent. Dorsal surface of trunk and anteriorly on tail above mid-lateral-line with many small melanophores. Trunk and anteriorly on tail below mid-lateral with dispersed large melanophores. Distinctive mid-lateral line of the largest melanophores running along tail.

Size. To about 130 mm TL.

Distribution (Figure 13). In New Zealand known from the northeast coast of the North Island and the Reinga Ridge at 435– 573 m. Elsewhere widespread and found on both sides of the North Atlantic Ocean including the Mediterranean Sea, the Pacific Ocean off Japan, Philippines, the Sala-y-Gomez Ridge (southeast Pacific Ocean), east and west coasts of Australia and east coast of Africa at 300–450 m (Iwamoto & Merrett, 1997).

Comparisons and remarks (Table 4). The original description of Gilbert and Hubbs (1920: 522) is excellent and Iwamoto & Merrett (1997: 518) also provided additional information on New Caledonia region specimens. A widely distributed species, so its presence in New Zealand waters is not surprising. The four New Zealand specimens are small and their size and fragility made specimen examination and description difficult. Surprisingly, all had 9 pelvic fin rays although Iwamoto & Merrett (1997) reported a mode of 8 rays. Comparison of the New Zealand specimens with the holotype, specimens from New Caledonia, Japan, both sides of the North Atlantic Ocean, and off Zanzibar (Table 4), shows overlap in the majority of characters and suggests a single widespread species. The only other recorded species in the genus is Hymenogadus tenuis (Gilbert & Hubbs 1917), known only from one 75 mm TL specimen (possibly immature) from off Oahu in the Hawaiian Islands at 485–512 m (265–280 fathoms). Hymenogadus tenuis was reported to have a shorter barbel, about 50% of orbit diameter, and about 10 inner gill rakers on the lower limb of the first arch (see Iwamoto 1990, p. 225) compared to barbel length of 50–70% orbit diameter and 11–15 inner gill rakers on the lower limb of the first arch in Hymenogadus gracilis (Iwamoto 1990).