Macrouridae Bonaparte, 1831

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 15-22

Family Macrouridae Bonaparte, 1831 (sensu Iwamoto et al. 2015)

[Japanese name: Sokodara-ka]

Diagnosis. Two dorsal fins well separated; first dorsal fin high and short-based; second dorsal fin long-based, poorly developed throughout its length; anal fin similar to, but usually much deeper than second dorsal fin; pelvic fin well developed with 5 or more soft rays; tail greatly elongate, without either caudal fin or caudal peduncle (pseudocaudal occasionally present and variously developed); mouth usually inferior to subterminal (rarely terminal); outermost gill slits restricted by skin folds attached to upper and lower ends of gill arch; gill rakers tubercular, not slender or lath-like; posttemporal fossa absent; body scales almost always ctenoid.

Remarks. This study confirms the occurrence of 76 grenadier species belonging to 18 genera from Japan and adjacent waters, of which 70 species in 15 genera are recognized within Japan’s EEZ.

Key to genera of grenadiers from Japan and adjacent waters

1a Infraorbital and preopercular ridges tightly adjoined, forming continuous bony ridge; preopercular ridge elongate posteroventrally and sharply pointed at posteroventral angle; snout long, protruding well beyond upper jaw, acutely pointed in lateral view in most species ......... Coelorinchus (25 spp.)

1b Infraorbital ridge not connected with preopercular ridge, separated by distinct gap; preopercular ridge not elongate posteroventrally nor sharply pointed at posteroventral angle; snout relatively short, moderately to scarcely protruding beyond upper jaw, conical to broadly rounded in lateral view .............................................................................................. 2

2a Anus (or periproct, if developed) abutting or only slightly separated from anal-fin origin.............................................. 3

2b Anus (or periproct, if developed) distinctly separated by several scale rows from anal-fin origin............................... 11

3a Gular region covered with net-like pattern or striation of black epithelium; broad areas of fine (microscopic), parallel, black lines (ventral striae) extending on ventral surfaces of chest, shoulder girdle, and belly, and along each side of isthmus; small lens-like structure of light organ on chest .................. 4

3b Gular region uniformly pale, dusky, dark, or blackish; ventral striae absent; no lens-like structure of light organ on chest anterior to pelvic fins ........................................................... 6

4a Gular region covered with net-like pattern of black epithelium; nasal bones stout, forming 3 horizontally flattened projections; outer pelvic-fin ray flattened, with narrow ribbon-like flange on free distal portion ........... Spicomacrurus ( S. kuronumai )

4b Gular region covered with striated pattern of black epithelium; nasal bones weak, usually paper-thin, not forming horizontal projections; outer pelvic-fin ray not flattened distally ......... 5

5a Second spinous ray of first dorsal fin smooth along its leading edge; trunk moderately deep, laterally compressed in cross section .......................................... Hymenocephalus (6 spp.)

5b Second spinous ray of first dorsal fin serrated along its leading edge; trunk shallow, almost cylindrical in cross section ......... .................................................... Hymenogadus ( H. gracilis )

6a Ventral aspects of body well forward so that anal-fin origin distinctly anterior to hind margin of first dorsal-fin base; scales on infraorbital ridge modified into coarsely spinulated, adherent scutes ............... * Sphagemacrurus ( S. pumiliceps )

6b Ventral aspects of body not well forward, and anal-fin origin below or posterior to hind margin of first dorsal-fin base; scales on infraorbital ridge normal or only slightly thickened .............................................................................................. 7

7a Second spinous ray of first dorsal fin smooth along its leading edge; periproct large, occupying more than half of distance between inner pelvic-fin bases to anal-fin origin; scales along anterior part of anal-fin base enlarged ................................... ...................................................... Trachonurus ( T. villosus )

7b Second spinous ray of first dorsal fin serrated along its leading edge; periproct small, its anterior margin far posterior to midway between inner pelvic-fin bases and anal-fin origin; scales along anterior part of anal-fin base not especially enlarged ................................................................................ 8

8a Head massive, soft, inflated, and broad; scales along anterior part of second dorsal-fin base enlarged.................................. ....................................................... Cetonurus ( C. globiceps )

8b Head not inflated, moderately compressed laterally; scales along anterior part of second dorsal-fin base not especially enlarged ................................................................................ 9

9a Periproct absent or rudimentary; reticulate structure absent on unexposed portion of body scales; branchiostegal rays 6 ...... ...................................................... Coryphaenoides (15 spp.)

9b Periproct narrow but distinct; reticulate structure broadly developed on unexposed portion of body scales; branchiostegal rays 7–8.............................................................................. 10

10a Dorsal surface of snout broadly naked anterior to line connecting lateral angles of snout; underside of head almost completely naked; posterior margin of upper jaw extending to vertical through hind rim of orbit or beyond; spinules on body scales arranged in widely spaced subparallel to slightly divergent rows..................... Asthenomacrurus ( A. victoris )

10b Dorsal surface of snout fully scaled; naked areas on underside of head confined to area above upper lip and anterior portions of mandibular rami; posterior margin of upper jaw not reaching vertical through hind rim of orbit; spinules on body scales arranged in quincunx order ........................................ ....................................................... Pseudonezumia (2 spp.)

11a Premaxillary teeth fang-like, arranged in 1 distinct row; chin barbel absent; trunk strongly compressed............................. ............................................ Odontomacrurus ( O. murrayi )

11b Premaxillary teeth not fang-like, relatively small, arranged in 2 or more rows; chin barbel present, variously developed; trunk moderately compressed ........................................... 12

12a Second spinous ray of first dorsal fin smooth along its leading edge; mandibular teeth arranged in 1 or 2 rows ............... 13

12b Second spinous ray of first dorsal fin variously serrated along its leading edge; mandibular teeth arranged in narrow to wide band...................................................................... 15

13a Mandibular teeth arranged in 2 irregular rows, with inner row slightly enlarged ............................................................ * Ventrifossa (in part; subgenus Atherodus : V. macroptera )

13b Mandibular teeth arranged in 1 distinct row..................... 14

14a Anterior dermal window of light organ large, bean-shaped, laterally expanded; mandibular teeth widely spaced canines; lower portion of gill membranes narrowly scaled along branchiostegal rays ....... Malacocephalus ( M. nipponensis )

14b Anterior dermal window of light organ small and circular; mandibular teeth small, not enlarged, tightly arranged; branchiostegal membranes entirely naked............................. ................................... Pseudocetonurus ( P. sp. cf. septifer )

15a Dorsal surface of snout broadly naked anterior to line connecting lateral angles of snout....... Kumba ( K. japonica )

15b Dorsal surface of snout completely or almost completely scaled ................................................................................ 16

16a Scales on infraorbital ridge modified into coarsely spinulated, adherent scutes.................................................................. 17

16b Scales on infraorbital ridge not especially modified ........ 18

17a Anus closer to pelvic-fin bases than to anal-fin origin; ventral aspects of body not positioned forward, and anal-fin origin below or posterior to hind margin of first dorsal-fin base .... .................................................................. Nezumia ( 7 spp.)

17b Anus closer to anal-fin origin than to pelvic-fin bases; ventral aspects of body positioned forward so that anal-fin origin distinctly anterior to hind margin of first dorsal-fin base ...... ...................................... * Sphagemacrurus ( S. pumiliceps )

18a Posterior margin of upper jaw extending beyond vertical through midorbit; posterior end of premaxillary tooth band extending beyond hind margin of maxillary process............ ................* Ventrifossa (in part; subgenera Sokodara and Ventrifossa : 7 spp.)

18b Posterior margin of upper jaw not or barely reaching vertical through midorbit; posterior end of premaxillary tooth band falling short of hind margin of maxillary process............. 19

19a Reticulate structure present on unexposed portion of body scales; body uniformly dark to blackish; posterior dermal window of light organ scarcely discernible externally ......... .......................................................... Kuronezumia (2 spp.)

19b Reticulate structure absent on body scales; body pale to dusky; posterior dermal window of light organ prominent, much larger than anterior window ........................................ ......................................... Lucigadus ( L. nigromarginatus )

Genus Asthenomacrurus Sazonov & Shcherbachev, 1982

[New Japanese name: Narakuno-sokodara-zoku]

Asthenomacrurus Sazonov & Shcherbachev, 1982:2 ( type species: Asthenomacrurus victoris Sazonov & Shcherbachev, 1982 , by original designation).

Diagnosis. Anus immediately anterior to anal-fin origin, surrounded by narrow but distinct periproct. Ventral light organ absent. Infraorbital ridge not connected with preopercular ridge, separated by distinct gap. Pelvic fin with 7–9 soft rays, its origin distinctly anterior to vertical through pectoral-fin base. Leading edge of second spinous ray of first dorsal fin weakly serrated. Head bones weak, flexible. Mouth large, posterior margin of upper jaw extending beyond vertical through hind rim of orbit. Nasal fossa not greatly enlarged. Chin barbel present. Teeth in narrow tapered bands in both jaws, none especially enlarged. Underside of head almost completely naked, including gular and branchiostegal membranes; dorsal surface of snout broadly naked anterior to line connecting lateral angles of snout; no modified scales along head ridges; tip and lateral angles of snout lacking prominent scutes. Body scales covered with short, erect, needle-like spinules in widely separated, subparallel to slightly divergent rows; buttresses of scale spinules narrowly developed; reticulate structure developed over entire surface of unexposed portion. Scales along second dorsal and anal fins not enlarged. Grooved lateral line complete. Cephalic sensory pores present on underside of head, scarcely discernible. Pyloric caeca very short, thick, 7–10. Branchiostegal rays 7, rarely 8. Body lacking prominent silvery reflections when fresh. [Modified from Iwamoto & Orlov (2008).]

Remarks. Asthenomacrurus appears to be most similar to Macrosmia Merrett, Sazonov & Shcherbachev, 1983 , and they share the following combination of features: branchiostegal rays7or rarely 8; anus immediately anterior to anal-fin origin; no ventral light organs; pelvic-fin base distinctly anterior to vertical through pectoral-fin base; first dorsal fin serrated along its leading edge; underside of head almost completely naked; dorsal surface of snout broadly naked anteriorly. Asthenomacrurus differs notably from Macrosmia in having a small nasal fossa (vs. greatly enlarged) and fewer pelvic-fin rays (7–9 vs. 11–12) and pyloric caeca (7–10 vs. 15–18). [Data for Macrosmia are from Merrett et al. (1983), Merrett & Iwamoto (2000), and Iwamoto et al. (2015).]

The genus currently comprises two bathyal species: A. victoris Sazonov & Shcherbachev, 1982 , the type species widely distributed in the Indo-West Pacific including Japan, plus a single record from the Mid-Atlantic Ridge; A. fragilis ( Garman, 1899) known only from the eastern central Pacific. Iwamoto & Orlov (2008) recently provided a redescription of A. victoris based on all the then-known specimens, giving a detailed comparison with A. fragilis .

Asthenomacrurus victoris Sazonov & Shcherbachev, 1982

[New Japanese name: Narakuno-sokodara]

( Figs. 9–15 ; Appendix 3-1A)

Asthenomacrurus victoris Sazonov & Shcherbachev, 1982:3 , fig. 1 (original description; holotype: ZMMGU P.15349, from Mid-Indian Ridge, in 3530 m; 2 paratypes from Western Australia and Japan); Iwamoto & Orlov 2008:126 (redescription; comparison with A. fragilis ).

Astenomacrurus [sic] victoris: Nakabo & Kai 2013:1874 (comments on Japanese record).

Diagnosis. Differs from its only congener, A. fragilis , in having the following combination of features: pelvic-fin rays 7–8; preoral length 26–40% HL; barbel length 11– 17% HL; cephalic sensory pores not prominent; pyloric caeca 8–10; gill rakers on first arch (outer/inner) 8– 12/12–16, on second arch 11–15/11–15. [Modified from Iwamoto & Orlov (2008).]

Material examined. 19 specimens. Holotype of Asthenomacrurus victoris: ZMMGU P. 15349 (female, 32.9 mm HL, 245+ mm TL), Mid-Indian Ridge, western Indian Ocean, 2.7667ºS, 65.6833ºE, 3530 m, R/V Vityaz’, cr. 31, sta. 4634, coll. V.M. Makushok, 12 Feb. 1960. Paratype of A. victoris: ZMMGU P. 16012 ( 1 male, 41.9 mm HL, 223+ mm TL), off Cape Leeuwin, Western Australia, Naturalist Plateau, southeastern Indian Ocean, 33.7000ºS, 110.8833ºE, 2320–2350 m, R/V Dmitriy Mendeleyev, cr. 16, coll. D.P. Andrianov. Non-types: Japan: BSKU 47934 ( 1 female, 41.1 mm HL, 192+ mm TL), BSKU 98223 ( 1 female, 28.9 mm HL, 135+ mm TL), off Shikoku, 32.2372ºN, 134.0220ºE, 2565–2647 m, R/V Tansei-maru, cr. KT-90-13, sta. T6, beam trawl, 3 Sept. 1990; NSMT-P 98028 ( 3 males, 28.5–31.8 mm HL, 142+– 176+ mm TL), southeast of Boso Peninsula, 34.7267ºN, 140.7400ºE, 2089–2096 m, R/V Tansei-maru, cr. KT-99- 06, sta. 15, 3-m ORE beam trawl, 22 Mar. 1999; BSKU 85666 ( 1 female, 45.9 mm HL, 197+ mm TL), BSKU 85667 ( 1 male, 44.1 mm HL, 265 mm TL), off Boso Peninsula, 34.3567ºN, 140.2190ºE, 2480–2516 m, R/V Tansei-maru, cr. KT-94-14, sta. 14-2, beam trawl, coll. H. Endo, 2 Sept. 1998; BSKU 45545 ( 1 female, 43.3 mm HL, 270 mm TL), off Kinkazan, 38.2355ºN, 142.4238ºE, 2167–2229 m, R/V Tansei-maru, cr. KT-89-03, sta. SR93, beam trawl, coll. O. Okamura and H. Endo, 11 Mar. 1989; KPM-NI 18570 ( 1 female, 35.1 mm HL, 181+ mm TL), KPM-NI 18571 ( 1 male, 32.8 mm HL, 202+ mm TL), off Tanega-shima Island, 29.8507ºN, 130.9281ºE, 1678–1769 m, R/V Tansei-maru, cr. KT-07-01, sta. YT-3, 3-m beam trawl, coll. T. Sato, 24 Feb. 2007. Australia: CSIRO H5304-13 ( 1 female, 44.2 mm HL, 204+ mm TL), off Victoria, 38.5667ºS, 149.4667ºE, 1954–1979 m; CSIRO H5304-38 ( 2 males, 41.2–42.6 mm HL, 190+–227+ mm TL), off Victoria, Tasman Sea, 38.5667ºS, 149.4667ºE, 1954–1979 m; CSIRO H5313-05 ( 1 male, 46.5 mm HL, 229+ mm TL), off Tasmania, Tasman Sea, 39.8000ºS, 149.1000ºE, 1946–1973 m. Porcupine Seabight: BMNH 1996.8.12.2–3 (2 sex undetermined, 26.5–29.6 mm HL, 144+–145+ mm TL), 50.4500ºN, 12.9833ºW, 2470–2500 m, Discovery, sta. 5141101, coll. N.R. Merrett, 29 Mar. 1982. Mid-Atlantic Ridge: ZMUB 19710 ( 1 female, 38.1 mm HL, 230 mm TL), 42.7667ºN, 29.2667ºW, 3036 m, R/V G.O. Sars, cr. MAR-ECO, supersta. 46, local sta. 372, 29-m otter trawl, 11 Jul. 2004.

Counts and measurements. Based on 19 specimens ( 26.5–46.5 mm HL, 135+– 270 mm TL). Counts: first dorsal-fin rays II,8–10; pectoral-fin rays i17–i21; pelvicfin rays 7–8; gill rakers on first arch (outer/inner) 8– 12/12–16, on second arch 12–15/11–15; longitudinal scales 28–39; transverse scale rows below first dorsalfin origin 6–9.5, below first dorsal-fin midbase 4.5–7.5, below second dorsal-fin origin 6–9; pyloric caeca 9–10.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 27–38 (36–57); orbit diameter 20–27 (29–39); postorbital length 44–51 (62–73); postrostral length 65– 76; orbit–preopercle distance 38–47 (53–67); suborbital width 15–20 (21–29); upper-jaw length 35–42 (51–60); length of rictus 31–37 (41–53); length of premaxillary tooth band 20–24 (29–34); preoral length 26–40 (37–58); distance between tip and lateral angle of snout 17–26 (26–39); snout width 24–37 (32–54); internasal width 22–33 (29–49); interorbital width 23–41 (31–58); body width over pectoral-fin bases 31–47 (41–70); body depth at first dorsal-fin origin 67–83 (100–120); body depth at anal-fin origin 53–80 (74–101); prepelvic length 91–108 (120–156); preanus length 124–140 (175–203); preanal length 126–145 (182–211); isthmus–pelvic distance 27–32 (38–48); isthmus–anus distance 59–71 (82–100); isthmus–anal distance 63–78 (90–109); pelvic–anal distance 33–55 (48–77); pelvic-fin length 54–78 (77– 114); pectoral-fin length 53–77 (81–110); predorsal length 100–113 (137–164); height of first dorsal fin 71– 83 (98–121); length of first dorsal-fin base 17–26 (24– 36); interdorsal length 21–40 (28–53); length of gill slit 15–22 (21–32); length of posterior nostril 6–13 (9–18); barbel length 11–16 (17–24).

Supplementary description based on Japanese specimens. A full description of A. victoris is unnecessary here, because most of its characters have been detailed by previous authors ( Sazonov & Shcherbachev 1982; Iwamoto & Orlov 2008). The following description therefore focuses on poorly known features based on the Japanese specimens examined, emphasizing their variation. General features of the species are shown in Figs. 9–10 .

Body scales small, thin, highly deciduous, covered with short, erect, needle-like spinules in widely separated, subparallel to slightly divergent, comb-like rows ( Fig. 11 A–B); scales on dorsum below interdorsal space vertically elongate, covered with 5–6 spinule rows (about 3 rows in smaller KPM specimens); middle row slightly enlarged, covered with 5–7 spinules (about 4 spinules in KPM specimens); height of spinules gradually increasing posteriorly, with last spinule in each row extending well beyond posterior scale margin; buttresses of spinules poorly developed; reticulate structure scattered over entire unexposed portion. Scales on isthmus longitudinally elongate, smaller than those on dorsum, covered with 1–3 rows of spinules; middle row distinctly longer than other rows ( Fig. 11 C–D). Predorsal scales covered with single row of spinules. Scales beneath gill covers and posterior to pectoral and pelvic fins cycloid. In KPM-NI 018571 ( 32.8 mm HL), scales on posterior half of belly also lacking spinules. Body fully scaled except for fins and periproct.

Head scales similar to those on body, but spinules much shorter and more erect. Scales on gill cover, postorbital canal, and posterior part of nape somewhat larger, covered with about 3 divergent rows of spinules. Other scales, especially those on dorsal surface of head, small and longitudinally elongate, covered with single row of spinules ( Fig. 11 E–F), giving striated appearance to head surfaces ( Fig. 12 ). Neither tubercles nor modified scales on tip and lateral angles of snout and head ridges.

Dorsal and lateral surfaces of head mostly covered with scales; naked region confined to top of snout anterior to lateral angles ( Figs. 12–13 ). Underside of head completely naked from snout tip to above posterior margin of upper jaw; ventral surface of preopercle naked; exposed portion of interopercle naked, but narrowly scaled posteriorly; mandibular rami, and gular and branchiostegal membranes lacking scales.

Cephalic sensory canals somewhat inflated when fresh ( Fig. 9 ) but shrunken in most preserved specimens, giving pointed appearance to snout (see also Iwamoto & Orlov 2008: fig. 2A). Due to this, general appearance of head often significantly changed after dehydration in alcohol.

Small inconspicuous sensory pores present along mandibular and infraorbital canals ( Fig. 13 ). No pores on preopercular, supraorbital, occipital, postorbital, and supratemporal canals. Lateral line complete and not interrupted throughout.

Color when fresh ( Fig. 9 ). Ground color of head and body uniformly dark brown in almost intact specimens ( Fig. 9A ); this dark color still prominent even when body scales completely missing ( Fig. 9B ), but ground color becoming dusky pink when epidermis badly damaged ( Fig. 9C ). Eye, gill cover, naked areas on head, gill membranes, and abdomen dull black; pectoral fin very dark; other fins uniformly dusky, but second spinous ray of first dorsal fin blackish.

Size. To about 27 cm TL ( BSKU 45545, 270 mm TL, off Kinkazan, Japan).

Sexual dimorphism. Compared with females, males have a wider posterior nostril [8.5–12.6% HL ( n = 9) vs. 6.3–9.1 ( n = 8); Fig. 14A ], a larger olfactory bulb (7.9–11.7% HL vs. 4.8–8.0%; Fig. 14B ), and more olfactory lamellae [16–20 (mean 17.6, n = 5) vs. 14–15 (mean 15.4, n = 5)]. In addition, the distal portion of the lamella in males is notably fimbriated, giving a concave appearance to the olfactory bulb ( Fig. 15A ). By contrast, that in females is simple or only weakly frilled, and the bulb is somewhat flat in appearance ( Fig. 15B ). These differences are emphasized in adult specimens, but obscure in juveniles of less than 32.5 mm HL.

Distribution. Sporadically recorded from the Indian and West Pacific Oceans, and Mid-Atlantic Ridge, at depths of 1642–3530 m ( Sazonov & Shcherbachev 1982; Parin et al. 1993; Iwamoto & Graham 2001; Iwamoto et al. 2004; Iwamoto & Orlov 2008). In Japan, known from off the Pacific coasts at depths of 1678–3460 m (Appendix 3-1A). Rare.

Remarks. Asthenomacrurus victoris was originally described by Sazonov & Shcherbachev (1982) based on three specimens collected from the Mid-Indian Ridge (type locality), Western Australia, and Japan (off Ibaraki Pref.). The holotype and the Australian paratype are deposited in the Zoological Museum of Moscow State University ( ZMMGU), and the author had an opportunity to examine the two specimens. According to Sazonov & Shcherbachev (1982), the holotype ( Fig. 10D ) and “the larger of the paratypes ” (= ZMMGU P.16012; Fig. 10E ) were immature females. The holotype was confirmed as a female, with well-developed ovaries in which there were large oocytes of about 0.6–1.0 mm in diameter. As typical of females, it also had a small olfactory bulb (7.0% of HL) consisting of 14 simple lamellae. The sex of the Australian paratype could not be determined with certainty, but its gonads seemed to be immature testes. In addition, its olfactory bulb was greatly enlarged (9.5% of HL), consisting of 17 fimbriated lamellae, which further suggests that it represents a male.

Prior to this study, A. victoris was represented by 12 specimens in museum collections, most of which are in poor condition ( Iwamoto & Orlov 2008). Additional specimens from Japan are well preserved, which allowed documentation of some squamation features of the species for the first time (see the Supplementary description). Although the scales of A. victoris are highly deciduous and easily missing when trawled, most scales are well preserved in the 43.3 mm HL specimen examined ( BSKU 45545; Figs. 9A , 10 A–C). In A. victoris , the dorsum scales below the interdorsal space are covered with short, erect, needle-like spinules in widely spaced parallel rows, and the morphology is similar to those of Kumba Marshall, 1973 . In contrast, the scales on the dorsal surface of the head are covered with a single row of erect spinules ( Fig. 11 E–F) that gives a striated appearance to the area ( Fig. 12 ). This characteristic striation is somewhat similar to that found in Mesovagus Nakayama & Endo, 2016 (replacement name for Mesobius Hubbs & Iwamoto, 1977 ). In addition, specimens of A. victoris are fragile and easily damaged when trawled, which caused an apparent difference in coloration (see the Supplementary description and Fig. 9 ).

In the original description of A. victoris, Sazonov & Shcherbachev (1982) described that “there are small pores in the … preopercular canal ( 2 in the lower part)”. However, the number was not confirmed due to their poor condition. Additional specimens from Japan revealed that the preopercular canal has not only two (or rarely three) pores on its lower part, but also a single pore on its upper end ( Fig. 13A ).

Sexual dimorphism of olfaction is well known in bathypelagic fishes such as ceratoid anglerfishes and several gonostmatids ( Cyclothone spp.), viz., males are macrosmatic with large modified olfactory organs,whereas those of females are poorly developed (e.g., Marshall 1967, 1979; Herring 2002). Although a few grenadiers are exclusively confined to the mid-water depth, most species are benthopelagic and closely associated with the sea floor. Marshall (1967), who studied the olfactory organs of various bathypelagic fishes, concluded that both sexes of bathypelagic grenadiers are microsmatic. He (1979:409) also noted that “in the benthopelagic fish fauna olfactory dimorphism seems to be confined to the halosaurs”.

Sexual dimorphism of the olfactory organ in grenadiers was first suggested by Merrett et al. (1983),who wrote that “males of several macrourid species are found to be macrosmatic (e.g., Trachyrinchus trachyrinchus ( Risso, 1810); Bathygadus melanobranchus Vaillant, 1888 ; Coryphaenoides (Coryphaenoides) güntheri ( Vaillant, 1888) and Nezumia aequalis (G̹nther, 1887)— personal observation, N.R.M.)”. Unfortunately, they did not specify which characters show the sexually dimorphic modification. The results of this study confirmed such a dimorphism expressed in A. victoris (see the Sexual dimorphism entry above).

Iwamoto & Orlov (2006) redescribed Pseudonezumia fragellicauda ( Koefoed, 1927) (as Paracetonurus fragellicauda ) based on its four syntypes and 44 specimens collected from the northeastern Atlantic and the Madagascar Plateau in the southwestern Indian Ocean. Two of these specimens collected from the Porcupine Seabight ( BMNH 1996.8.12.2–3, 26.5–29.6 mm HL, 144+–145+ mm TL) are re-identified here as A. victoris by having a broad naked area on the dorsal surface of the snout (vs. completely scaled in P. fragellicauda ) and short, thick pyloric caeca (vs. slender and long).

Figures

FIGURE 9. Fresh specimens of Asthenomacrurus victoris. (A) BSKU 45545, 43.3 mm HL, 270 mm TL, off Kinkazan, Miyagi Pref., Pacific, 2167–2229 m depth (reversed); (B) BSKU 85666, 45.9 mm HL, 197+ mm TL, off Boso Peninsula, Chiba Pref., Pacific, 2480–2516 m depth; (C) BSKU 47934, 41.1 mm HL, 192+ mm TL, off Shikoku, Pacific, 2565–2647 m depth. Lateral views. [Photos: BSKU]

FIGURE 10. Preserved specimens of Asthenomacrurus victoris. (A–C) BSKU 45545, 43.3 mm HL, 270 mm TL, off Kinkazan, Miyagi Pref., Pacific, 2167–2229 m depth; (D) ZMMGU P.15349, holotype, 32.9 mm HL, 245+ mm TL, Mid-Indian Ridge, western Indian Ocean, 3530 m depth; (E) ZMMGU P.16012, paratype, 41.9 mm HL, 223+ mm TL, Western Australia, southeastern Indian Ocean, 2320–2350 m depth. (A, D–E) Lateral views; (B) dorsal and (C) ventral views of the head and trunk. [Photos: N. Nakayama]

FIGURE 11. Scanning electron micrographs showing scales of Asthenomacrurus victoris. BSKU 45545, 43.3 mm HL. Scales (A–B) from the dorsum below the interdorsal space; (C–D) from the chest posterior to the isthmus; (E–F) from the interorbital area. (A, C, E) Views from above; (B, D, F) oblique views. [Photos: N. Nakayama]

FIGURE 12. Dorsal surface of the snout of Asthenomacrurus victoris showing squamation and spinulation on the head scales. BSKU 45545, 43.3 mm HL. Preserved condition, stained with Cyanine Blue solution. [Photo: N. Nakayama]

FIGURE 13. Diagrammatic illustrations showing the cephalic sensory system and naked areas (gray) of Asthenomacrurus victoris. BSKU 45545, 43.3 mm HL. (A) Lateral, (B) dorsal, and (C) ventral views of the head and trunk. [Illustrations: N. Nakayama]

FIGURE 14. Scatter diagrams showing relationships of the (A) length of the posterior nostril and (B) length of the olfactory bulb (as % HL) to HL (mm) in Asthenomacrurus victoris. Circles and squares indicate males and females respectively.

FIGURE 15. Olfactory bulbs of Asthenomacrurus victoris. (A) BSKU 85667, male, 44.1 mm HL; (B) BSKU 85666, female, 45.9 mm HL. [Photos: N. Nakayama]