Postodius sanguineus, 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 : 506-512

Postodius sanguineus sp. nov.

[Japanese name: Chigoke-subeyokoebi, new]

( Figs 17–22 )

Type material. Holotype: ovigerous female, 3.4 mm (OMNH-Ar-12241), Mihonoseki, Matsue City , Shimane Prefecture, 35°33′25′′N, 133°16′55′′E, 0.1–0.5 m depth, on a bryozoan Watersipora sp. , 30 May 2020, coll. S. Morihisa. Paratypes: ovigerous female, 2.9 mm (OMNH-Ar-12242); male, 2.0 mm (OMNH-Ar-12243); male, 1.7 mm (OMNH-Ar-12244), same data as holotype.

Type locality. Mihonoseki , Matsue City, Shimane Prefecture in Japan .

Etymology. From the Latin sanguineus (= blood-red), referring to the body coloration.

Description of female. Based on holotype, ovigerous female, 3.4 mm (OMNH-Ar-12241). Body ( Fig. 17 ), pleonites 1 and 2 each with indistinct posterodorsal projection, pleonite 3 with blunt projection at mid-length.

Head ( Figs 17 , 18 ). Lateral cephalic lobe projected anteroventrally. Eyes 7.3% length of body. Antenna 1 stout; length ratio of peduncular articles 1–3 1:0.7:0.45; accessory flagellum minute, tip with 2 setae; primary flagellum with 6 articles, article 1 elongate, each article with several aesthetascs. Antenna 2 also stout, shorter than antenna 1, with ratio of lengths of peduncular articles 3–5 1:1.5:1.2; flagellum with 6 articles, article 1 long. Mandible, incisor narrow, dorsal margin with 13–14 denticles; left lacinia mobilis slender, bearing 12 denticles; accessory blades slender, 14–15 in number; anterior margin distal to palp slightly expanded; palp long, length ratio of palp articles 1–3 in left 1:2.35:2.6, article 3 with numerous fine setae on anterior margin and lateral surface and 3 thick setae on tip. Maxilla 1, inner plate longish pear-shaped, with single seta on tip; medial margin of outer plate bearing 8 robust setae and many fine setae, palp with 1 long and 2 minute setae on tip. Maxilliped, inner plate distal margin bearing 2 minute robust setae; outer plate long, exceeding distal end of palp article 4; palp short, articles 2 and 3 setose mediodistally, article 4 short, ca. 0.15 times length of article 3.

Pereon ( Fig. 19 ). Gnathopod 1 small; coxa narrowed distally; basis widened proximally, anterior margin with single simple seta, posterior margin bare; posterodistal projection of propodus with 1 robust, 1 plumose and 2 short setae; dactylus bearing 3 needle-shaped and 2 plumose setae. Gnathopod 2 larger than gnathopod 1; coxa with blunt projection on posterior margin, process on inner surface indistinct; basis with single anterior and 2+2 posterior plumose setae; ischium with robust seta at posterodistal corner; merus projected posterodistally, with 4 and 5 robust setae on posterior margin and at posterodistal corner, respectively; carpus produced posterodistally, with 7 robust setae; propodus wide, ca. 0.45 times length of coxa, palm almost straight, with many serrations, posterodistal corner and medial surface with 3 and 4 robust setae, respectively; 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 4 anterior and 6 posterior plumose setae, posterodistal corner bearing 2 plumose, 1 robust and 3 short setae; ischium with 3 robust setae on posterior margin; merus bearing 4 anterior, 1 anterodistal, 2 posterior, 3 posterolateral, 1 posteromedial and 1 posterodistal robust setae; carpus with 1 posterolateral, 1 posteromedial and 3 posterodistal robust setae; propodus with 4 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 4 slightly longer than pereopod 3; coxa wide, inner surface with very large triangular process; basis with 13 anterior and 6 posterior plumose setae, posterodistal corner bearing 3 plumose, 3 robust and 1 short setae; ischium with 3 posterior robust setae; merus with 3 anterior, 1 anterodistal, 3 posterior and 3 posteromedial robust setae; carpus with 1 posterior and 3 posterodistal robust setae; propodus with 1 single and 4 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 5 shorter than pereopod 4; coxa lobate, anteroventral margin with 3 inner and 1 marginal plumose setae; basis produced posterodistally, posterior margin smooth, anterior margin with 6 plumose setae, anterodistal corner bearing robust seta; ischium with 4 robust setae on anterior margin; merus with 6 anterior, 2 anterolateral, 1 anteromedial, 3 posterior and 1 posterodistal robust setae; carpus with 1 anterolateral, 1 anteromedial and 5 anterodistal robust setae; propodus with 4 couples of robust setae posteriorly; dactylus with plumose seta. Pereopod 6 slightly longer than pereopod 5; coxa lobate, anterior margin with 6 plumose setae; basis produced posterodistally, posterior margin weakly convex, anterior margin with 2+1 plumose setae and 4 robust setae, anterodistal corner bearing 2 robust setae; ischium with 4 anterior robust setae; merus with 5 anterior, 2 anteromedial, 4 posterior and 1 posterodistal robust setae; carpus with 1 anterior, 2 anteromedial and 4 anterodistal robust setae; propodus with 2 single and 2 couples of robust setae anteriorly; dactylus with plumose seta. Pereopod 7 a little shorter than pereopod 6; coxa small, unlobed, anterior margin with 10 plumose setae; basis wide, produced posterodistally, posterior margin moderately convex, anterior margin with single plumose seta and 5 short robust setae, anteromedial surface with several short robust setae, anterodistal corner bearing 2 robust setae; ischium with 3 anterior robust setae; merus with 3 anterior, 2 anteromedial, 2 anterodistal and 4 posterior robust setae; carpus with 1 anterolateral, 3 anteromedial and 4 anterodistal robust setae; propodus with 2 single and 2 couples of robust setae anteriorly; dactylus with plumose seta.

Pleon ( Fig. 20 ). Pleopods, pleopod 3 shortest; peduncles each with many plumose setae laterally and 2 coupling hooks mediodistally; outer rami longer than inner, outer rami with 13, 13, 12 articles, respectively, inner rami with 11 articles. Uropod 1 long; peduncle bearing 10 lateral, 1 laterodistal and 4 medial robust setae; outer ramus with 7 lateral, 2 medial and 3 terminal robust setae, inner ramus with 3 lateral, 5 medial and 3 terminal robust setae. Uropod 2 short, ca. 0.7 times length of uropod 1; peduncle bearing 5 lateral, 1 laterodistal and 1 medial robust setae; outer ramus ca. 3/4 times length of inner ramus, with 4 lateral and 3 terminal robust setae, inner ramus with 3 lateral, 3 medial and 3 terminal robust setae. Uropod 3 shorter than uropod 2; peduncle with 1 lateral and 1 laterodistal robust setae; outer ramus ca. 0.6 times length of inner ramus, with 3 lateral robust setae and terminal short seta, inner ramus with 5 lateral and 4 medial robust setae and terminal short seta. Telson long-triangular, tip with 2 minute excavations.

Description of male [based on paratype, 2.0 mm (OMNH-Ar-12243)]. Eyes larger than those of female. Antenna 1 ( Fig. 20 M-A1) stouter than that of female; accessory flagellum longer; primary flagellum with 5 articles, article 1 very long, each articles bearing many aesthetascs. Gnathopod 2 ( Fig. 20 M-G2) subequal to that of female except for oostegite, but coxa inner surface with small triangular process, basis lacking plumose setae and propodus more slender. Pereopod 3, basis without plumose setae. Pereopod 7 ( Fig. 20 M-RP7), coxa with single plumose seta on anterior margin; basis roundish, anterior margin without plumose seta. Uropod 1, peduncle with 5 lateral, 1 laterodistal and 2 medial robust setae.

Coloration in life [based on holotype, ovigerous female, 3.4 mm (OMNH-Ar-12241) and paratype, male, 1.7 mm (OMNH-Ar-12244)]. Female ( Fig. 21 ). Eyes dark red. Body and coxae light blood-red, with ambiguous white spots, dorsal margin white and light blood-red. Antennae white and partly red. Pereopods 3–7 except coxae and urosome light orange. Male ( Fig. 22 ). Eyes dark red. Body and coxae dark blood-red, with ambiguous white spots, dorsal margin white and dark blood-red. Antennae dark blood-red and partly dark red. Pereopods 3–7 except coxae and urosome light to pale orange.

Remarks. Postodius sanguineus sp. nov. is characterized by the wider propodus of the gnathopod 2 in both sexes. The plumose setae on the bases posterior margins of the female gnathopod 2 and pereopods 3, 4 are probably unique in the genus, whereas Ariyama (2011) did not describe the female setation. In addition, the body coloration of P. sanguineus is distinctive in the genus.

Habitat. Found on a bryozoan Watersipora sp. , 0.1–0.5 m depth.

Distribution. Only Mihonoseki, Matsue City in Japan.

Figures

FIGURE 17. Postodius sanguineus sp. nov. Holotype: ovigerous female, 3.4 mm (OMNH-Ar-12241). Habitus.

FIGURE 18. Postodius sanguineus sp. nov. Holotype: ovigerous female, 3.4 mm (OMNH-Ar-12241). Scales: 0.05 mm.

FIGURE 19. Postodius sanguineus sp. nov. Holotype: ovigerous female, 3.4 mm (OMNH-Ar-12241). Gill on pereopod 6 lost, oostegites on pereopods 3–5 omitted. Scales: 0.1 mm.

FIGURE 20. Postodius sanguineus sp. nov. All but M: holotype, ovigerous female, 3.4 mm (OMNH-Ar-12241); M: paratype, male, 2.0 mm (OMNH-Ar-12243). Scales: 0.1 mm.

FIGURE 21. Postodius sanguineus sp. nov. Photograph of holotype, ovigerous female, 3.4 mm (OMNH-Ar-12241) by H. Ariyama.

FIGURE 22. Postodius sanguineus sp. nov. Photograph of paratype, male, 1.7 mm (OMNH-Ar-12244) by H. Ariyama.