Antarctodius japonicus Ariyama, 2011

Ariyama, Hiroyuki, 2021, Five species of the family Odiidae (Crustacea: Amphipoda) collected from Japan with descriptions of a new genus and four new species, Zootaxa 5067 (4), pp. 485-516 : 513-515

Antarctodius japonicus Ariyama, 2011

[Japanese name: Mukashi-subeyokoebi]

( Figs 23 , 24 )

Antarctodius japonicus Ariyama, 2011: 34 , figs 22–25.

Material examined. Female, 3.2 mm (OMNH-Ar-12245), off Jōgashima Island, Miura City , Kanagawa Prefecture, 35°07′14′′N, 139°34′24′′E, 91-95 m depth, sandy bottom, using dredge, 17 June 2013, coll. H. Kohtsuka.

Material for comparison. Holotype: male, 2.9 mm (1.7 mm in a straight line) (NSMT-Cr-21285), midway between Kuchinotsu and Ohyano, Ariake Sound, 32°34′N, 130°15′E, 47 m depth, sandy gravel bottom, using Smith-McIntyre grab, 5 June 1997, coll. M. Azuma.

Description of female. Based on female, 3.2 mm (OMNH-Ar-12245). Body ( Fig. 23 ), pleonites 1–3 each lacking dorsal projection, pleonite 3 with small projection posteroventrally.

Head ( Figs 23 , 24 ). Lateral cephalic lobe projected anteroventrally. Eyes 9.3% length of body. Antenna 1 stout; length ratio of peduncular articles 1–3 1:0.8:0.35; accessory flagellum present, minute, tip with 1 seta; primary flagellum with 6 articles, article 1 not elongate, each article with a few aesthetascs. Maxilla 1 small; inner plate longish pear-shaped, with 3 plumose setae on tip; medial margin of outer plate bearing 8 robust setae and many thick and fine setae, palp 2-articulated, tip heavily setose. Maxilliped, inner plate distal margin bearing 3 robust setae; outer plate truncate, slightly exceeding distal end of palp article 2, laterodistal corner with 7 robust setae; palp articles 2 and 3 setose mediodistally, article 4 long triangular, about 0.7 times length of article 3.

Pereon and pleon ( Fig. 24 ). Gnathopod 1 slender; coxa narrow; basis slightly widened proximally, anterior margin with several short setae, posterior margin bearing 6 long setae; posterodistal corner of propodus with long robust seta and 3 short setae; dactylus complexly trifurcated, exceeding tip of robust seta of propodus, bearing 2 plumose and 1 short setae. Gnathopod 2 larger than gnathopod 1; coxa almost straight, inner surface with tiny process; basis with single short seta on anterior margin; merus truncate distally, posterodistal corner with 2 robust setae; carpus produced posterodistally, with 2 anterodistal, 2 lateral, 3 posterior and 8 posterodistal robust setae; propodus short, with 2 anterior, 2 anterodistal, 5 lateral and 5 medial robust setae, palm slightly curved, with many serrations; dactylus short, posterior margin with small spine. Pereopod 7, coxa small, unlobed, anterodistal margin with 3 short setae, gill present; basis wide, produced posterodistally, posterior margin slightly concave, anterior margin with 8 plumose and 12 robust setae, anterolateral surface and anterodistal corner bearing 5 and 1 robust setae, respectively, inner surface with many plumose (?) setae; ischium with 1 anterior and 1 anterodistal robust setae; merus with 2 anterior, 7 anteromedial, 2 anterodistal, 4 posterior and 1 posterodistal robust setae; carpus–dactylus lost. Telson deeply cleft, both tips each with minute seta.

Description of male [based on holotype, male, 2.9 mm (1.7 mm in a straight line) (NSMT-Cr-21285)]. Antenna 1 with large accessary flagellum, tip with 2 setae ( Fig. 24 M-AF). Pereopod 7, coxa with damaged fragment of gill. Both overlooked in Ariyama (2011).

Coloration in life. Unknown.

Remarks. Ariyama (2011) described this species based on a single male specimen. The present female specimen, however, can be identified as Antarctodius japonicus , because most characters including important ones are shared with the holotype (ex. maxilla 1, maxilliped, gnathopods and telson), although there are some trifle differences.

Habitat. Found on sandy gravel bottom and sandy bottom, 47–95 m depth.

Distribution. Ariake Sound in Kyūshū ( Ariyama 2011) and off Jōgashima Island, Miura City (present study), both in Japan.

Figures

FIGURE 23. Antarctodius japonicus Ariyama, 2011. Female, 3.2 mm (OMNH-Ar-12245). Habitus.

FIGURE 24. Antarctodius japonicus Ariyama, 2011. All but M: female, 3.2 mm (OMNH-Ar-12245); M: holotype, male, 2.9 mm (1.7 mm in a straight line) (NSMT-Cr-21285). Scales: 0.1 mm.