Metodius leucomaculatus, 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 : 493-499

Metodius leucomaculatus sp. nov.

[Japanese name: Shirahoshi-subeyokoebi, new]

( Figs 7–11 )

Type material. Holotype: ovigerous female, 7.1 mm (OMNH-Ar-12233), off Jōgashima Island , Miura City, Kanagawa Prefecture, 35°08′25′′N, 139°32′30′′E, 147–250 m depth, using dredge, 12 February 2015, coll. H. Kohtsuka. Paratypes: ovigerous female, 8.6 mm (OMNH-Ar-12234), same locality, 35°08′18′′N, 139°34′41′′E, 86.8–87.7 m depth, sandy bottom, using dredge, 29 July 2014, coll. H. Kohtsuka ; ovigerous female, 6.8 mm (OMNH-Ar-12235), same locality, 35°08′16′′N, 139°33′28′′E, 100–103 m depth, using dredge, 20 January 2015, coll. H. Kohtsuka ; male, 7.0 mm (OMNH-Ar-12236), same locality, 35°08′22′′N, 139°33′41′′E, 95.2–95.9 m depth, gravel and sand bottom, using dredge, 5 November 2015, coll. H. Kohtsuka.

Type locality. Off Jōgashima Island , Miura City, Kanagawa Prefecture in Japan .

Etymology. From the Greek leuco (= white) + the Latin maculatus (= maculate), referring to the body coloration.

Description of female. Based on holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233). Body ( Fig. 7 ), pereonites 6, 7 with small and medium dorsal projections, respectively; pleonites 1–3 each with dorsal projection.

Head ( Figs 7 , 8 ). Lateral cephalic lobe projected anteroventrally. Eyes large, 9.9% length of body. Antenna 1 somewhat slender; length ratio of peduncular articles 1–3 1:0.55:0.25; accessory flagellum minute, tip with 1 thick and 1 simple setae; primary flagellum with 8 articles, article 1 elongate, each article with several aesthetascs. Antenna 2 slender, almost same length as antenna 1, with ratio of lengths of peduncular articles 3–5 1:1.85:1.4; flagellum with 10 articles, article 1 long. Mandible, incisor wide, distal margin with 9–11 denticles; left lacinia mobilis bearing 10 denticles; accessory blades 14 in number; palp long, length ratio of palp articles 1–3 in right 1:4.1:4.0, with numerous fine setae on anterior margin and lateral surface and 3 thick setae on tip. Maxilla 1, inner plate oval, with single seta on tip; medial margin of outer plate bearing 6 large and ca. 30 small robust setae and many simple setae, dorsal and ventral surfaces covered with fine setae, palp very short. Maxilliped, inner plate slightly projected mediodistally, with many plumose setae distally and medially; outer plate rounded, mediodistal margin distinctly serrated, distal margin setose; laterodistal corners of palp articles 1, 2 each bearing single robust seta, article 3 setose mediodistally, article 4 slender, ca. 0.6 times length of article 3.

Pereon ( Fig. 9 ). Gnathopod 1 small; coxa narrow; basis slightly narrowed distally, anterior margin with single plumose seta proximally, posterior margin lacking plumose seta; posterodistal projection of propodus with 1 robust, 1 plumose and several short setae; dactylus far exceeding tip of robust setae on propodus, bearing small robust seta, plumose seta and several short setae. Gnathopod 2 greatly larger than gnathopod 1; coxa with blunt projection on posterior margin, inner surface with tiny process; basis without plumose setae on anterior and posterior margins, posterodistal corner weakly projected, bearing 3 robust setae; ischium slightly projected posterodistally; merus with 2 robust setae at posterodistal corner; carpus projected posterodistally, posterior margin with 5 robust setae; propodus long and wide, almost same length as coxa, anterodistal corner projected and excavated, palm slightly rounded, with numerous denticles, posterodistal corner and posterior margin with single large and 7 small robust setae, respectively; dactylus slender, slightly exceeding posterodistal corner of propodus. Pereopod 3 a little shorter than gnathopod 2; coxa with blunt projection and plumose seta posteriorly, inner surface with small triangular process; basis without plumose setae, but with 9 and 4 robust setae on posterior margin and at posterodistal corner, respectively; ischium with 2 small robust setae on posteromedial surface; merus bearing 1 anterodistal and 1 posterodistal robust setae; carpus with 2 anterodistal and 4 posterodistal robust setae, posterior margin with 1 single and 3 couples of robust setae; propodus with 8 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 4 almost same length as pereopod 3; coxa wide, inner surface with large triangular process; basis without plumose setae, but with 10 and 4 robust setae on posterior margin and at posterodistal corner, respectively; ischium with posteromedial robust seta; merus with 1 anterodistal, 2 posterolateral, 2 posteromedial and 3 posterodistal robust setae; carpus with 3 anterodistal, 4 posterolateral, 5 posteromedial and 3 posterodistal robust setae; propodus with 8 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 5 slightly shorter than pereopod 4; coxa lobate, anteroventral margin with 6 inner and marginal simple setae; basis produced posterodistally, posterior margin distinctly convex distally, anterior part with 8 lateral, 3 medial and 2 distal robust setae; ischium with 3 robust setae on anterior margin; merus with 5 anterolateral, 1 anterodistal, 1 posterior and 1 posterodistal robust setae; carpus with 5 anterolateral, 5 anteromedial and 2 anterodistal robust setae; propodus with 1 single and 7 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 6 slightly longer than pereopod 5; coxa lobate, anterior margin with many plumose setae and strange-shaped thick seta; basis produced posterodistally, posterior margin distinctly convex distally, anterolateral surface with several proximal simple setae and 5 robust setae, anterior margin bearing 10 robust setae, anterodistal corner with 2 robust setae; ischium with 3 anterior robust setae; merus bearing 5 anterior, 1 anteromedial, 2 anterodistal, 2 posterior and 1 posterodistal robust setae; carpus with 6 couples of robust setae anteriorly; propodus with 8 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 7 a little shorter than pereopod 6; coxa small, unlobed, anterior margin with 13 plumose setae; basis wide, produced posterodistally, distal end of posterior margin strongly convex, anterior part with 12 marginal, 3 lateral and 2 distal robust setae, inner surface bearing many plumose setae; ischium with 3 anterior and 1 anteromedial robust setae; merus bearing 5 anterior, 2 anteromedial, 2 anterodistal and 1 posterior robust setae; carpus with 5 couples of robust setae anteriorly; propodus bearing 8 couples of robust setae anteriorly; dactylus with plumose seta.

Pleon ( Fig. 10 ). Pleopods, pleopod 3 shortest; peduncles each with many plumose setae laterally and 2 coupling hooks mediodistally, peduncle of pleopod 3 also bearing 5 robust and 3 simple setae medially and 6 plumose setae posteriorly; outer rami longer than inner, outer and inner rami with 18, 20, 19 and 18, 16, 17 articles, respectively. Uropod 1 long; peduncle bearing 5 lateral, 1 laterodistal, 10 medial and 1 mediodistal robust setae [lost in part; with 11 lateral, 1 laterodistal, 10 medial and 1 mediodistal robust setae in paratype, ovigerous female, 6.8 mm (OMNH-Ar-12235)]; outer ramus with 8 lateral, 8 medial and 3 terminal robust setae, inner ramus with 6 lateral, 9 medial and 3 terminal robust setae. Uropod 2 short, ca. 3/4 times length of uropod 1; peduncle bearing 7 lateral and 1 laterodistal robust setae; outer ramus ca. 0.8 times length of inner ramus, with 7 lateral, 2 medial and 3 terminal robust setae, inner ramus with 6 lateral, 8 medial and 3 terminal robust setae. Uropod 3 almost same length as uropod 2; peduncle with 2 lateral and 1 laterodistal robust setae; outer ramus ca. 0.6 times length of inner ramus, with 5 lateral and 3 medial robust setae, inner ramus with 6 lateral and 8 medial robust setae and terminal short seta. Telson long triangular, tip acutely projected, not incised.

Description of male [based on paratype, 7.0 mm (OMNH-Ar-12236)]. Eyes larger than those of female. Antenna 1 ( Fig. 10 M-RA1), peduncular article 3 shorter than that of female; primary flagellum with 10 articles, each bearing many aesthetascs. Gnathopod 2 ( Fig. 10 M-RG2) subequal to that of female except for oostegite. Pereopod 7 ( Fig. 10 M-RP7), coxa anterior margin with 10 plumose setae; basis shorter than that of female, with 9 anterior, 4 anterolateral and 2 anterodistal robust setae, inner surface bearing only 2 plumose setae.

Coloration in life [based on holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233); Fig. 11 ]. Eyes red. Body and coxae dark olive green, with ca. 20 white spots, middorsal margin of each pereonites and pleonites red surrounded by white, middle part of pereonite 4 and dorsal part of coxa 4 yellowish white (probably due to reflection of light). Gnathopod 2 white. Pereopods 3–7 except coxae and urosomite light olive green.

Remarks. Metodius leucomaculatus sp. nov. differs from M. cyanomaculatus sp. nov. in the larger size, the dorsal projections on the pereonite 7 and pleonites, the distinct serration on the maxilliped outer plate, the longer dactylus of the gnathopod 1, the more slender bases of the pereopods, and the coloration.

Habitat. Found on gravel and sand bottom, 86–250 m depth.

Distribution. Only off Jōgashima Island, Miura City in Japan.

Figures

FIGURE 7. Metodius leucomaculatus gen. et sp. nov. Holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233). Habitus.

FIGURE 8. Metodius leucomaculatus gen. et sp. nov. Holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233). Scales: 0.1 mm.

FIGURE 9. Metodius leucomaculatus gen. et sp. nov. Holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233). Oostegites on pereopods 3–5 omitted. Scales: 0.2 mm.

FIGURE 10. Metodius leucomaculatus gen. et sp. nov. All but M: holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233); M: paratype, male, 7.0 mm (OMNH-Ar-12236). Scales: 0.2 mm.

FIGURE 11. Metodius leucomaculatus gen. et sp. nov. Photograph of holotype, ovigerous female, 7.1 mm (OMNH-Ar-12233) by H. Kohtsuka.