Ventrifossa saikaiensis Okamura, 1984

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 310-312

Ventrifossa saikaiensis Okamura, 1984

[Japanese name: Saikai-hige]

( Figs. 205 E–F, 216; Appendix 3-13D)

Ventrifossa saikaiensis Okamura, 1984a:209 , fig. 147 (original description; holotype: BSKU 28004, from Okinawa Trough, 28º50.0ʹN, 127º14.0ʹE, in 700–740 m; 11 paratypes from Okinawa Trough, in 560–755 m; new Japanese name: “Saikai-hige”); Okamura 1988:453, pl. 373, fig. F (compiled); Nakabo 1993:359 (in key; Japan); Nakabo 2000:423 (in key; Japan); Nakabo 2002:423 (in key; Japan); Yoda et al. 2002:11 (listed; East China and Yellow Seas); Chiou et al. 2004a:48, fig. 23, table 1 (brief description; 19 spec. from Da-xi; first record from Taiwan); Shinohara et al. 2005:418 (listed; Ryukyu Islands); Shao et al. 2008b: table 2 (46 spec. listed from northeastern and southwestern Taiwan, and South China Sea); Nakabo & Kai 2013:499 (in key; Japan); Iwamoto et al. 2015:116 (brief description; 64 spec. from northeastern Taiwan and East China Sea off Japan, including holotype); Motomura 2020:40 (listed; Japan).

Ventrifossa divergens (not Gilbert & Hubbs 1920): Chiou et al. 2004a:46, fig. 19, table 1 (brief description; 2 spec. from Dong-gang and Da-xi; first record from Taiwan) [fide Iwamoto et al. (2015)].

Diagnosis. Second spinous ray of first dorsal fin finely serrated along its leading edge; first dorsal and anal fins uniformly dusky; front of premaxillary ascending process lacking prominent black spot; oral cavity pale; median rostral ridge, leading edges of snout, supranarial ridges, and suborbital shelves not prominently blackish; body uniformly brown, except for dark abdomen; scale pockets narrowly outlined in dark; snout low, slightly protruding beyond upper jaw, preoral length 13–21% HL; no scute-like scale at snout tip; body scales covered with short, moderately erect, needle-like spinules in quincunx order; spinules on scales along second dorsal-fin base not enlarged; body scales moderately small, transverse scale rows below midbase of first dorsal fin 6–7.5, below second dorsal-fin origin 6–7.5; longitudinal scales 37–45; area of spinuleless scales posterior to first dorsal-fin base only narrowly developed; outer series of premaxillary teeth slightly enlarged; mandibular teeth arranged in narrow tapered band; suborbital shelf not greatly constricted anteriorly; inner gill rakers on first arch 15–19, outer gill rakers on second arch 15–17; orbit large, greatest diameter 28–38% HL; suborbital width 13–17% HL; upper-jaw length 45–52% HL; interorbital space broad, width 26–33% HL; chin barbel long, length 30–38% HL; pectoral-fin length 59–72% HL.

Material examined. 20 specimens. Holotype of Ventrifossa saikaiensis: BSKU 28004 (54.7 mm HL, 307+ mm TL), northwest of Amami-oshima Island, Kagoshima Pref., Japan, Okinawa Trough , East China Sea , 28.8333ºN, 127.2333ºE, 700–740 m, F/ V Ryoanmaru, No. 28, tr. 59, bottom trawl, coll. Y. Kinoshita and S. Hagino, 16 Mar. 1978 . Paratypes of V. saikaiensis: BSKU 26324 (1, 37.4 mm HL, 209+ mm TL), off Senkaku Islands, Okinawa Trough , 25.6283ºN, 122.8933ºE, 560– 692 m, F/ V Yuryo-maru, No. 8, tr. 3, bottom trawl, coll. T. Kitajima et al., 14 Jan. 1978 ; * BSKU 28005 (1, 41.4 mm HL, 184+ mm TL) , BSKU 28006 (1, 51.5 mm HL, 249+ mm TL) , BSKU 28007 (1, 54.9 mm HL, 207+ mm TL) , BSKU 28008 (1, 53.0 mm HL, 293+ mm TL), collected with holotype ; * BSKU 27664 (1, 36.2 mm HL, 198+ mm TL) , * BSKU 27665 (1, 42.1 mm HL, 200+ mm TL), west of Okinawa-jima Island, Okinawa Trough , 28.7333ºN, 127.0167ºE, 610–640 m, F/ V Ryoan-maru, No. 28, tr. 49, bottom trawl, coll. Y. Kinoshita and S. Hagino, 11 Mar. 1978 ; BSKU 27576 (1, 57.2 mm HL, 287+ mm TL) , BSKU 27577 (1, 50.4 mm HL, 222+ mm TL) , * BSKU 27578 (1, 52.2 mm HL, 240+ mm TL) , * BSKU 27579 (1, 52.6 mm HL, 294+ mm TL), northwest of Amamioshima Island, Okinawa Trough , 28.7167ºN, 127.2333ºE, 750–755 m, F/ V Ryoan-maru, No. 28, tr. 48, bottom trawl, coll. Y. Kinoshita and S. Hagino, 11 Mar. 1978 . Nontypes : Japan : BSKU 26325 (1, 53.7 mm HL, 280+ mm TL), off Senkaku Islands, Okinawa Trough , 25.6283ºN, 122.8933ºE, 560–692 m, F/ V Yuryo-maru, No. 8, tr. 3, bottom trawl, coll. T. Kitajima et al., 14 Jan. 1978 ; FFNU P-00738 (8, 24.7–47.7 mm HL, 155+–265+ mm TL), north of Hokutosekibi Bank, East China Sea , 26.4928ºN, 125.1432ºE, 675 m, T/ V Nagasaki-maru, cr. N260, sta. S, 3-m ORE beam trawl, coll. J. Hashimoto, 21 Jun. 2008 .

Counts and measurements. Based on 16 specimens (27.4–57.4 mm HL, 155+–307+ mm TL). Counts: first dorsal-fin rays II,9–11; pectoral-fin rays i18–i23; pelvicfin rays 8–9; gill rakers on first arch (outer/inner) 10– 14/15–19, on second arch 15–17/14–18; longitudinal scales 37–45; transverse scale rows below first dorsalfin origin 7.5–10, below first dorsal-fin midbase 6–7.5, below second dorsal-fin origin 6–7.5.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 27–33 (35–43); orbit diameter 28–38 (39–49); postorbital length 41–49 (54–63); postrostral length 72– 80; orbit–preopercle distance 42–46 (54–63); suborbital width 13–17 (17–23); upper-jaw length 45–52 (59–69); length of rictus 39–43 (51–58); length of premaxillary tooth band 33–39 (44–51); preoral length 13–21 (18–29); distance between tip and lateral angle of snout 16–22 (21–28); snout width 30–40 (39–52); internasal width 23– 30 (30–39); interorbital width 26–33 (34–44); occipital width 15–18 (20–24); body width over pectoral-fin bases 39–60 (50–80); body depth at first dorsal-fin origin 82–97 (107–125); body depth at anal-fin origin 65–83 (86–106); prepelvic length 103–133 (134–171); preanus length 113–142 (146–178); preanal length 132–161 (169–203); isthmus–pelvic distance 39–48 (50–65); isthmus–anus distance 47–56 (61–74); isthmus–anal distance 70–77 (92–103); pelvic–anal distance 27–35 (35–47); anus–anal distance 18–25 (24–32); pelvic-fin length 37–40 (48– 52); pectoral-fin length 59–72 (75–94); predorsal length 93–116 (121–155); length of first dorsal-fin base 25–32 (33–43); interdorsal length 45–63 (58–87); length of gill slit 26–35 (34–46); length of posterior nostril 2–6 (3–8); barbel length 30–38 (39–49).

Size. To about 31 cm TL ( BSKU 28004 , holotype) .

Distribution. So far known only from the Okinawa Trough and the northern South China Sea at depths of 520‾ 764 m ( Chiou et al. 2004a; Shao et al. 2008b; this study; Appendix 3-13D). Rare in Japanese waters.

Remarks. For further morphological information see the original description given by Okamura (1984a). This species was originally described from the Okinawa Trough in the East China Sea, and additional specimens were subsequently recorded from Taiwan ( Chiou et al. 2004a; Shao et al. 2008b; Iwamoto et al. 2015). Chiou et al. (2004a) first recorded V. divergens Gilbert & Hubbs, 1920 from Taiwanese waters based on two specimens obtained at fish markets in Dong-gang and Da-xi, but their specimens were re-identified as V. saikaiensis by Iwamoto et al. (2015).

Relationships and comparisons. Ventrifossa saikaiensis closely resembles V. divergens distributed in the western Pacific from Taiwan to Indonesia. According to Iwamoto et al. (2015:117), the two species are readily distinguished by coloration: the body of V. saikaiensis is uniformly brownish, whereas in V. divergens , silvery reflections are present on the sides of the body. In Japanese waters, V. saikaiensis is most similar to V. garmani ( Jordan & Gilbert in Jordan & Starks, 1904) in having a broad interorbital space (26–33% HL). However, it readily differs from the latter species in having needlelike spinules on the body scales (vs. broadly triangular), a wider snout (snout width 30–40% HL vs. 25–29%), and a deeper suborbital space (suborbital width 13–17% HL vs. 11–13%).

Figures

FIGURE 205. Scanning electron micrographs showing body scales (from the dorsum below the interdorsal space) of three species of Ventrifossa. (A–B) V. longibarbata, BSKU 27124, 55.4 mm HL; (C–D) V. rhipidodorsalis, BSKU 27146, paratype, 54.5 mm HL; (E–F) V. saikaiensis, BSKU 28006, paratype, 51.2 mm HL. (A, C, E) Views from above; (B, D, F) oblique views. [Photos: NSMT]