Metodius cyanomaculatus, Ariyama, 2021

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 : 488-493

Metodius cyanomaculatus sp. nov.

[Japanese name: Rurihoshi-subeyokoebi, new]

( Figs 2–6 )

Type material. Holotype: ovigerous female, 5.0 mm (OMNH-Ar-12230), Nodahama Beach, Izu-ōshima Island ( Ōshima Town ), Tokyo Prefecture, 34°47′49′′N, 139°21′31′′E, 12 m depth, using SCUBA, 24 March 2015, coll. O. Hoshino. Paratypes: male, 3.5 mm (OMNH-Ar-12231), same locality, 10 m depth, using SCUBA, 4 April 2015, coll. O. Hoshino ; male, 2.8 mm (OMNH-Ar-12232), same locality, 10 m depth, using SCUBA, sandy bottom, 23 December 2015, coll. O. Hoshino.

Type locality. Nodahama Beach , Izu-ōshima Island, Tokyo Prefecture in Japan .

Etymology. From the Greek cyano (= dark blue) + the Latin maculatus (= maculate), referring to the body coloration.

Description of female. Based on holotype, ovigerous female, 5.0 mm (OMNH-Ar-12230). Body ( Fig. 2 ), pereonites and pleonites lacking dorsal projection.

Head ( Figs 2 , 3 ). Lateral cephalic lobe acutely projected anteroventrally. Eyes large, 8.3% length of body. Antenna 1 stout; length ratio of peduncular articles 1–3 1:0.65:0.3; accessory flagellum slender, tip with 1 plumose and 2 simple setae; primary flagellum with 7 articles, article 1 elongate, each article with several aesthetascs. Antenna 2 also stout, almost same length as antenna 1, with ratio of lengths of peduncular articles 3–5 1:1.7:1.5; flagellum with 5 articles, article 1 long. Mandible, incisor wide, distal margin with 9–10 denticles; left lacinia mobilis bearing 10 denticles; accessory blades 13 in number; palp long, length ratio of palp articles 1–3 1:3.55:2.65, article 3 with numerous fine setae on anterior margin and lateral surface and 3 thick setae on tip. Maxilla 1, inner plate ovoid, with 3 setae on tip; medial margin of outer plate bearing 4 large and ca. 20 small robust setae, dorsal surface covered with many fine setae, palp very short. Maxilliped, inner plate slightly projected mediodistally, bearing 8 plumose setae; outer plate rounded, mediodistal margin minutely serrated, distal margin with several thick setae; laterodistal corners of palp articles 1, 2 each bearing a few robust setae, article 3 setose mediodistally, article 4 slender, about half length of article 3.

Pereon ( Fig. 4 ). Gnathopod 1 small; coxa narrow; basis slightly widened proximally, anterior and posterior margins without plumose setae; posterodistal projection of propodus with 1 robust, 1 plumose and several short setae; dactylus slightly exceeding tip of robust setae on propodus, bearing small robust seta and several short setae. Gnathopod 2 far larger than gnathopod 1; coxa with blunt projection and plumose seta on posterior margin, inner surface with tiny process; basis without plumose setae on anterior and posterior margins, posterodistal corner weakly projected, bearing robust seta; ischium also projected posterodistally; merus with 3 and 3 robust setae on posterior margin and at posterodistal corner, respectively; carpus projected posterodistally, tip with 4 robust setae medially; propodus long and wide, ca. 0.9 times length of coxa, anterodistal corner projected and excavated, palm slightly rounded, with many serrations, posterodistal corner and posterior margin with 9 and 2 robust setae, respectively; dactylus slender, tip narrowed, slightly exceeding posterodistal corner of propodus. Pereopod 3 longer than gnathopod 2; coxa with blunt projection and plumose seta posteriorly, inner surface with small triangular process; basis with 14 plumose setae on anterior margin and 5 small robust setae on posterior margin, posterodistal corner bearing 6 robust setae; ischium with 2 small robust setae on posterior margin; merus bearing 2 anterior, 3 anterodistal, 4 posterolateral, 5 posteromedial and 2 posterodistal robust setae; carpus with 4 anterodistal, 2 posterolateral, 4 posteromedial and 5 posterodistal robust setae; propodus with 6 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 4 longer than pereopod 3; coxa wide, inner surface with large triangular process; basis with 4 plumose and many short setae on anterior margin and 7 robust setae on posterolateral margin, posterodistal corner bearing 6 robust setae; ischium with 3 posterolateral and 2 posteromedial robust setae; merus with 1 anterior, 3 anterodistal, 2 posterolateral, 7 posteromedial and 2 posterodistal robust setae; carpus with 3 anterodistal, 4 posterolateral, 4 posteromedial and 5 posterodistal robust setae; propodus with 1 single and 5 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 5 slightly longer than pereopod 4; coxa lobate, anteroventral margin with 6 plumose setae on inner surface; basis produced posterodistally, posterior margin weakly convex, anteroproximal margin with 1 plumose and 1 robust setae, anterolateral surface and anterodistal corner bearing 9 and 2 robust setae, respectively; ischium with 4 robust setae on anterior margin; merus with 6 anterolateral, 2 anteromedial, 2 anterodistal, 1 posterior and 1 posterodistal robust setae; carpus with 4 anterolateral, 3 anteromedial and 3 anterodistal robust setae; propodus with 1 single and 6 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 6 slightly longer than pereopod 5; coxa lobate, anterior margin with 10 plumose setae; basis produced posterodistally, posterior margin weakly convex, anterolateral surface with many robust setae, anterodistal corner bearing 3 robust setae; ischium with 4 anterior robust setae; merus with 5 anterolateral, 2 anteromedial, 2 anterodistal and 2 posterior robust setae; carpus with 2 anterolateral, 4 anteromedial and 4 anterodistal robust setae; propodus with 7 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 7 a little longer than pereopod 6; coxa small, unlobed, anterior margin with ca. 20 plumose setae; basis wide, produced posterodistally, posterior margin strongly convex, anterior part with 8 marginal, 5 lateral and 2 distal robust setae, inner surface bearing many plumose setae; ischium with 3 anterior and 1 medial robust setae; merus bearing 3 anterior, 4 anteromedial, 2 anterodistal, 2 posterior and 1 posterodistal robust setae; carpus with 3 anterolateral, 3 anteromedial and 4 anterodistal robust setae; propodus with 1 single and 6 couples of robust setae anteriorly; dactylus with plumose seta.

Pleon ( Fig. 5 ). Pleopods, pleopod 3 shortest; peduncles each with many plumose setae laterally and 2 coupling hooks mediodistally, peduncle of pleopod 3 also bearing 4 robust and 5 simple setae mediodistally; outer rami longer than inner, outer and inner rami with 17, 18, 16 and 15, 16, 15 articles, respectively. Uropod 1 long; peduncle bearing 15 lateral, 1 laterodistal, 4 medial and 1 mediodistal robust setae; outer ramus with 12 lateral, 7 medial and 4 terminal robust setae, inner ramus with 6 lateral, 8 medial and 4 terminal robust setae. Uropod 2 short, ca. 0.7 times length of uropod 1; peduncle bearing 7 lateral, 1 laterodistal and 1 mediodistal robust setae; outer ramus ca. 3/4 times length of inner ramus, with 6 lateral, 2 medial and 3 terminal robust setae, inner ramus with 5 lateral, 5 medial and 3 terminal robust setae. Uropod 3 almost same length as uropod 2; peduncle with laterodistal robust seta; outer ramus ca. 0.6 times length of inner ramus, with 5 lateral and 3 medial robust setae and terminal short seta, inner ramus with 6 lateral and 7 medial robust setae and terminal short seta. Telson long triangular, tip minutely incised, with short seta.

Description of male [based on paratype, 3.5 mm (OMNH-Ar-12231)]. Eyes larger than those of female. Antenna 1 ( Fig. 5 M-A1), primary flagellum stouter than that of female, with 8 articles, each bearing numerous aesthetascs. Gnathopod 2 ( Fig. 5 M-G2) subequal to that of female except for oostegite, but propodus more slender. Pereopod 7 ( Fig. 5 M-P7), coxa anterior margin with 8 plumose setae; basis more slender than that of female, with 7 anterior, 5 anterolateral and 2 anterodistal robust setae, inner surface lacking plumose setae.

Coloration in life [based on paratype, male, 2.8 mm (OMNH-Ar-12232); Fig. 6 ]. Head white, eyes red. Body and coxae brown, with ca. 15 bright blue spots and several white spots, dorsal margin of body framed in red. Antennae white and partly bright red. Pereopods 5–7 except coxae white.

Habitat. Found on sandy bottom, 10–12 m depth.

Distribution. Only Izu-ōshima Island in Japan.

Figures

FIGURE 2. Metodius cyanomaculatus gen. et sp. nov. Holotype, ovigerous female, 5.0 mm (OMNH-Ar-12230). Habitus.

FIGURE 3. Metodius cyanomaculatus gen. et sp. nov. Holotype, ovigerous female, 5.0 mm (OMNH-Ar-12230). Scales: 0.1 mm.

FIGURE 4. Metodius cyanomaculatus gen. et sp. nov. Holotype, ovigerous female, 5.0 mm (OMNH-Ar-12230). Oostegites on pereopods 3–5 omitted. Scales: 0.1 mm.

FIGURE 5. Metodius cyanomaculatus gen. et sp. nov. All but M: holotype, ovigerous female, 5.0 mm (OMNH-Ar-12230); M: paratype, male, 3.5 mm (OMNH-Ar-12231). Scales: 0.1 mm.

FIGURE 6. Metodius cyanomaculatus gen. et sp. nov. In situ photograph of paratype, male, 2.8 mm (OMNH-Ar-12232) taken on Nodahama Beach, Izu-ōshima Island (type locality, 10 m depth) on 23 December 2015 by O. Hoshino.