Hymenogadus gracilis ( Gilbert & Hubbs, 1920 )

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 223-224

Hymenogadus gracilis ( Gilbert & Hubbs, 1920) [Japanese name: Oni-sujidara]

( Fig. 147 ; Appendix 3-9A)

Hymenocephalus gracilis Gilbert & Hubbs, 1920:522 , fig. 31 [original description; holotype: USNM 78227, from off southern Luzon Island, Albatross sta. 5292, 13º28ʹ45ʺN, 121º01ʹ12ʺE, in 162 ftm (296 m)]; Kamohara 1936:934 (first record from Japan; 3 spec. from Kochi); Okada & Matsubara 1938:451 (in key; Japan; new Japanese name: “Onisujidara”); Kamohara 1938:69 (brief description; 3 spec. from Kochi Pref.; new Japanese name: “Hoso-suji-dara”); Kamohara 1950:278 (listed; Kochi Pref.); Kamohara 1952:96 (brief description; 3 spec. from Kochi Pref.); Matsubara 1955:1314 (in key; Japan); Kamohara 1958:73 (listed; Kochi Pref.); Kamohara 1964:96 (listed; Kochi Pref.); Tatara et al. 1965:121 (listed; off Shikoku); Shinohara et al. 2001:305 (142 spec. listed from Tosa Bay); Shao et al. 2008b: table 2 (3 spec. listed from northeastern Taiwan and South China Sea); Iwatsuki et al. 2017:32 (listed; Hyuga-nada).

Hymenogadus gracilis: Okamura 1970a:61 , pl. XVIII, text-fig. 27 (description; 60 spec. from Pacific off southern Japan from Owase to Totoro); Okamura 1970b: table 1 (listed; Japan); Tominaga & Uyeno 1981:489 (listed; Japan); Okamura 1984a:201, 359, fig. 143 [brief description; 5 spec. from Okinawa Trough; photo based on BSKU spec. (catalog no. unknown)]; Okamura 1984b:93, pl. 80, fig. H (compiled); Okamura 1988:93, pl. 80, fig. H (compiled); Nakabo 1993:354 (in key; Japan); Okamura 1997:128, fig. 4 (compiled); Nakabo 2000:418 (in key; Japan); Nakabo 2002:418 (in key; Japan); Yoda et al. 2002:11 (listed; East China and Yellow Seas); Chiou et al. 2004a:44, fig. 13, table 1 (brief description; 2 spec. from Nan-fang-ao; first record from Taiwan); Shinohara et al. 2005:418 (listed; Ryukyu Islands); Nakabo & Kai 2013:494 (in key; Japan); Iwamoto et al. 2015:78 (brief description; 6 spec. from northeastern Taiwan and Philippines); Motomura 2020:39 (listed; Japan).

Hymenocephalus striatissimus (not Jordan & Gilbert in Jordan & Starks 1904): Suzuki & Kataoka 1997:81, pl. 32, fig. 173 (brief description; 1 spec. from Kumano-nada) [re-identified here from figure].

Diagnosis. Hymenogadus gracilis readily differs from its only congener, H. tenuis ( Gilbert & Hubbs, 1917) , in having a longer chin barbel (19–33% HL vs. 12%) and higher counts of pectoral-fin rays (i14–i19 vs. i12) and outer gill rakers on the second arch (13–19 vs. 10). [Data for the two species are compiled from Gilbert & Hubbs (1917), Marshall & Iwamoto (1973), McMillan & Iwamoto (2014), Schwarzhans (2014), and this study.]

Material examined. 6 specimens. Japan : BSKU 112920 (1, 24.6 mm HL, 131+ mm TL), off Okitsu , Tosa Bay, 280–320 m, F/ V Kosei-maru, bottom trawl, coll. N. Nakayama et al., 24 Jan. 2014 ; BSKU 118435 (1, 22.2 mm HL, 122+ mm TL), off mouth of Niyodo River , Tosa Bay, 300 m, FRV Tosa-Kaiyo-maru, bottom otter trawl, coll. by T. Ohkawa, 14 Oct. 2015 ; BSKU 121258 (1, 22.7 mm HL, 113+ mm TL) , BSKU 121264 (1, 22.7 mm HL, 103+ mm TL) , BSKU 121268 (1, 22.8 mm HL, 119+ mm TL), off mouth of Niyodo River , Tosa Bay, 200 m, FRV Tosa-Kaiyo-maru, bottom otter trawl, coll. by T. Ohkawa, 24 Dec. 2015 ; * BSKU 91754 (1, 20.9 mm HL, 117+ mm TL), Mimase fish market, bottom trawl, coll. N. Nakayama, 12 Oct. 2007 .

Counts and measurements. Based on 5 specimens (22.2–24.6 mm HL, 103+–131+ mm TL). Counts: first dorsal-fin rays II,10–11; pectoral-fin rays i15–i17; pelvicfin rays 8; gill rakers on first arch (outer/inner) 10–13/15– 17, on second arch 14–18/15–17; longitudinal scales 18–21; transverse scale rows below first dorsal-fin origin 3–3.5, below first dorsal-fin midbase 2–2.5, below second dorsal-fin origin 3–3.5, above anal-fin origin 7–9.5.

The following measurements are in% of HL, followed by those in % of PRL in parentheses: snout length 24–28 (31–36); orbit diameter 34–36 (44–47); postorbital length 42–46 (53–58); postrostral length 77–80; orbit–preopercle distance 35–37 (45–47); suborbital width 8–9 (11–12); upper-jaw length 41–44 (54–57); length of rictus 37–39 (48–50); length of premaxillary tooth band 32–36 (41– 45); preoral length 13–14 (16–18); distance between tip and lateral angle of snout 13–15 (17–20); snout width 21– 25 (27–32); internasal width 18–19 (23–25); interorbital width 16–18 (20–23); occipital width 7–8 (9–11); body width over pectoral-fin bases 53–61 (68–78); body depth at first dorsal-fin origin 54–59 (70–76); body depth at analfin origin 44–50 (57–62); prepelvic length 95–102 (123– 133); preanal length 158–173 (204–217); isthmus–pelvic distance 46–49 (60–63); isthmus–anal distance 109–127 (140–160); pelvic–anal distance 63–79 (81–99); pelvicfin length 40–48 (52–60); pectoral-fin length 42–51 (54– 64); predorsal length 108–113 (140–143); height of first dorsal fin 62–68 (77–89); length of first dorsal-fin base 32–40 (41–52); interdorsal length 57–68 (73–89); length of gill slit 22–24 (29–31); length of posterior nostril 4–7 (6–9); barbel length 21–27 (28–34).

Size. To about 13 cm TL ( McMillan & Iwamoto 2014).

Distribution. Widely known from the North Atlantic, Mediterranean, southwestern Indian Ocean off Mozambique, South China Sea off the Philippines, and Pacific including Japan, Taiwan, New Zealand, and the Sala y Gomez Ridge, at depths of about 182–657 m ( Marshall & Iwamoto 1973; Sazonov & Iwamoto 1992; Anderson 1996; Iwamoto & Merrett 1997; Shao et al. 2008a, 2008b; Last et al. 2014; McMillan & Iwamoto 2014; Schwarzhans 2014; this study). In Japan, known from off the Pacific coasts northward to the Izu Peninsula (138.96ºE) and the Okinawa Trough at depths of 182‾ 385 m (Appendix 3-9A). Common.

Remarks. For a full description see the original description given by Gilbert & Hubbs (1920). Additional descriptions were also provided by Okamura (1970a), Marshall & Iwamoto (1973), and Iwamoto & Merrett (1997).Otolith morphology was described by Schwarzhans (2014). Hymenocephalus gracilis was widely recorded from the world’s oceans, with the type locality in the South China Sea off the Philippines (see the Distribution). McMillan & Iwamoto (2014) compared the New Zealand specimens with those collected from various parts of its rage (including the holotype), and showed no significant differences in major meristic and morphometric characters. This species is currently considered to have a nearly cosmopolitan distribution ( McMillan & Iwamoto 2014; Schwarzhans 2014), whereas its only congener, H. tenuis , is represented by only the holotype collected from Hawaii.

Figures

FIGURE 147. Fresh specimen of Hymenogadus gracilis. BSKU 91754, 20.9 mm HL, 117+ mm TL, Mimase fish market, Kochi Pref., Pacific. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: N. Nakayama]