Postodius albifacies, 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 : 500-502

Postodius albifacies sp. nov.

[Japanese name: Shirogao-subeyokoebi, new]

( Figs 12–16 )

Type material. Holotype: female with juveniles, 4.1 mm (OMNH-Ar-12237), Ōsezaki, Numazu City , Shizuoka Prefecture, 35°01′36′′N, 138°47′05′′E, 20 m depth, rocky reef with soft corals, using SCUBA, 9 April 2015, coll. Y. Kawahara. Paratypes: ovigerous female, 3.8 mm (OMNH-Ar-12238); ovigerous female, 2.7 mm (OMNH-Ar-12239); male, 2.4 mm (OMNH-Ar-12240), same data as holotype.

Type locality. Ōsezaki , Numazu City, Shizuoka Prefecture in Japan .

Etymology. From the Latin albi (= white) + facies (= face), referring to the head coloration.

Description of female. Based on holotype, female with juveniles, 4.1 mm (OMNH-Ar-12237). Body ( Fig. 12 ), pereonite 7 and pleonites 1–3 each with small dorsal projection.

Head ( Figs 12 , 13 ). Lateral cephalic lobe projected anteroventrally. Eyes 6.8% length of body. Antenna 1 stout; length ratio of peduncular articles 1–3 1:0.65:0.4; accessory flagellum minute, tip with 3 setae; primary flagellum with 5 articles, article 1 elongate, each article with several aesthetascs. Antenna 2 also stout, slightly shorter than antenna 1, with ratio of lengths of peduncular articles 3–5 1:2.2:1.65; flagellum with 5 articles, article 1 long. Mandible, incisor narrow, dorsal margin with 13–14 denticles; left lacinia mobilis slender, bearing 5 denticles; accessory blades slender, 11 in number; anterior margin distal to palp expanded; palp long, length ratio of palp articles 1–3 1:4.75:3.9, article 3 with numerous fine setae on lateral surface and 3 thick setae on tip. Maxilla 1, inner plate pearshaped, with 2 setae on tip; medial margin of outer plate bearing 7 large and ca. 20 small robust setae and many slender setae, palp with long apical seta and many short marginal setae. Maxilliped, inner plate distal margin bearing 3 robust setae; outer plate long, exceeding distal end of palp article 4; palp short, articles 2, 3 setose mediodistally, article 4 short, about 0.15 times length of article 3.

Pereon ( Fig. 14 ). Gnathopod 1 small; coxa narrowed distally; basis slightly widened proximally, anterior margin with single plumose seta and many short setae, posterior margin bearing a few short setae; posterodistal projection of propodus with 1 robust, 2 plumose and several short setae; dactylus bearing 2 needle-shaped and 3 plumose setae. Gnathopod 2 larger than gnathopod 1; coxa with blunt projection on posterior margin, inner surface with tiny process; basis with 3 plumose and many short setae on anterior margin, posterior margin bare, posterodistal corner bearing 1 robust and 2 slender setae; ischium with long robust seta at posterodistal corner; merus slightly projected posterodistally, with 5 and 2 robust setae on posterior margin and at posterodistal corner, respectively; carpus produced posterodistally, with 10 robust setae; propodus wide, ca. 0.45 times length of coxa, anterodistal corner slightly projected, palm straight, with many serrations, posterodistal corner with 2 robust setae; dactylus stout, with nail, tip not reaching posterodistal corner of propodus. Pereopod 3 far longer than gnathopod 2; coxa with blunt projection posteriorly, inner surface with small triangular process; basis with 17 plumose setae on anterior margin and 6 small robust setae on posterior margin, posterodistal corner bearing 6 robust setae; ischium with 2 small robust setae on posterior margin, posterodistal corner bearing 2 robust setae; merus with 6 anterior, 2 anterodistal, 4 posterior, 4 posterolateral, 2 posteromedial and 1 posterodistal robust setae; carpus with 3 posterolateral, 3 posteromedial and 6 posterodistal robust setae; propodus with 5 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 4 longer than pereopod 3; coxa wide, inner surface with very large triangular process; basis with>20 plumose and many short setae on anterior margin and 7 robust setae on posterolateral margin, posterodistal corner bearing 6 robust setae; ischium with 11 posterior, 5 posterolateral and 2 posteromedial robust setae; merus with 5 anterior, 1 anterodistal, 3 posterior, 8 posterolateral, 10 posteromedial and 3 posterodistal robust setae; carpus with 1 anterodistal, 1 posterior, 2 posterolateral, 5 posteromedial and 6 posterodistal robust setae; propodus with 1 single and 5 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 5 almost same length as pereopod 4; coxa lobate, anteroventral margin with>10 plumose setae on inner surface; basis produced posterodistally, posterior margin smooth, anterior margin with ca. 15 plumose and 8 robust setae, anterodistal corner bearing 3 robust setae; ischium with 10 robust setae on anterior margin; merus with 8 anterior, 9 anteromedial, 2 anterodistal, 7 posterior and 1 posterodistal robust setae; carpus with 2 anterior, 6 anteromedial and 5 anterodistal robust setae; propodus with 1 single and 4 couples of robust setae posteriorly. Pereopod 6 slightly shorter than pereopod 5; coxa lobate, anterior margin with>20 plumose setae; basis produced posterodistally, posterior margin smooth, anterior margin with 6 plumose setae and ca. 10 short robust setae, anterolateral surface with several short robust setae, anterodistal corner bearing 2 robust setae; ischium with 7 anterior robust setae; merus with 6 anterior, 8 anteromedial, 2 anterodistal, 7 posterior and 1 posterodistal robust setae; carpus with 1 anterior, 1 anterolateral, 4 anteromedial and 5 anterodistal robust setae; propodus with 1 single and 5 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 7 a little longer than pereopod 6; coxa small, unlobed, anterior margin with ca. 15 plumose setae; basis wide, produced posterodistally, posterior margin weakly convex, anterior margin with 11 plumose setae and 8 short robust setae, anterolateral surface with several short robust setae, anterodistal corner bearing 3 robust setae, inner surface with many plumose setae; ischium with 5 anterior and 7 anteromedial robust setae; merus with 5 anterior, 9 anteromedial, 3 anterodistal, 8 posterior and 1 posterodistal robust setae; carpus with 1 anterior, 3 anteromedial and 6 anterodistal robust setae; propodus bearing 1 single and 4 couples of robust setae anteriorly; dactylus with plumose seta.

Pleon ( Fig. 15 ). Pleopods, pleopod 3 shortest; peduncles each with many plumose setae laterally and several plumose setae and 2 coupling hooks medially; outer rami longer than inner, outer and inner rami with 18, 18, 16 and 17, 16, 14 articles, respectively. Uropod 1 long; peduncle bearing 29 lateral, 1 laterodistal and 9 medial robust setae; outer ramus with 13 lateral, 6 medial and 3 terminal robust setae, inner ramus with 7 lateral, 9 medial and 3 terminal robust setae. Uropod 2 short, ca. 3/4 times length of uropod 1; peduncle bearing 10 lateral, 1 laterodistal and 2 medial robust setae; outer ramus ca. 3/4 times length of inner ramus, with 8 lateral, 1 medial and 3 terminal robust setae, inner ramus with 6 lateral, 6 medial and 3 terminal robust setae. Uropod 3 slightly shorter than uropod 2; peduncle with 1 lateral and 1 laterodistal robust setae; outer ramus ca. 0.6 times length of inner ramus, with 5 lateral and 1 medial robust setae and terminal short seta, inner ramus with 8 lateral and 7 medial robust setae and terminal short seta. Telson roundish long-triangular, tip with minute excavation.

Description of male [based on paratype, 2.4 mm (OMNH-Ar-12240)]. Antenna 1 ( Fig. 15 M-A1), accessory flagellum longer than that of female; primary flagellum with 6 articles, article 1 very long, each articles bearing many aesthetascs. Gnathopod 2 ( Fig. 15 M-G2) subequal to that of female except for oostegite, but basis without plumose setae and propodus more slender. Pereopod 3, basis with 3 plumose setae on anterior margin. Pereopod 7 ( Fig. 15 M-P7), coxa anterior margin with 4 plumose setae; basis anterior margin with single plumose seta and 6 robust setae, inner surface lacking plumose setae. Uropod 1, peduncle with 12 lateral, 1 laterodistal and 4 medial robust setae.

Coloration in life (based on female, size unknown; Fig. 16 ). Head white, eyes light red. Body and coxae light orange, with 11 violet curved lines, middle dorsal margin of each pereonites and pleonites red. Antennae white and partly red. Pereopods 3–7 also light orange.

Remarks. Postodius albifacies sp. nov. can be distinguished from the other Postodius species by the coloration and the combination of the shapes of gnathopod 2 and pereopods 3, 7 (see the above key). The uropod 1 peduncle with many lateral and medial robust setae is probably distinctive, although those in the females of four species are not shown in Ariyama (2011).

Habitat. Found on rocky reef with soft corals, 20 m depth.

Distribution. Only Ōsezaki, Numazu City in Japan.

Figures

FIGURE 12. Postodius albifacies sp. nov. Holotype, female with juveniles, 4.1 mm (OMNH-Ar-12237). Habitus.

FIGURE 13. Postodius albifacies sp. nov. Holotype, female with juveniles, 4.1 mm (OMNH-Ar-12237). Scales: 0.05 mm.

FIGURE 14. Postodius albifacies sp. nov. Holotype, female with juveniles, 4.1 mm (OMNH-Ar-12237). Oostegites on pereopods 3–5 omitted. Scales: 0.1 mm.

FIGURE 15. Postodius albifacies sp. nov. All but M: holotype, female with juveniles, 4.1 mm (OMNH-Ar-12237); M: paratype, male, 2.4 mm (OMNH-Ar-12240). Scales: 0.1 mm.

FIGURE 16. Postodius albifacies sp. nov. In situ photograph of a female (size unknown) taken at Ōsezaki (type locality, 20 m depth) on 4 April 2015 by Y. Kawahara.