(Figs 10–14)
Material examined. Holotype: male, 4.3 mm (OMNH-Ar- 7716), off Soneura, Kata Bay, Mie Prefecture (33 ° 58 ' 10 ''N, 135 ° 12 ' 35 ''E), 30 m deep, mud bottom, Ekman–Birge sampler, 27 August 1998, coll. H. Yokoyama. Allotype: ovigerous female, 4.1 mm (OMNH-Ar- 7717), same data as holotype. Paratypes: 3 males, 4.5, 3.1, 2.7 mm (OMNH-Ar- 7718–7720) and 1 female, 1.9 mm (OMNH-Ar- 7721), same data as holotype; 1 male, 2.4 mm (OMNH-Ar- 7722), same place, 31 m deep, sandy-mud bottom, Ekman–Birge sampler, 27 August 1998, coll. H. Yokoyama; 1 male, 6.0 mm (OMNH-Ar- 7723) and 1 female, 4.1 mm (OMNH-Ar- 7724), Owase Bay, Mie Prefecture, ca. 25 m deep, mud bottom, Ekman–Birge sampler, 13 May 1997, coll. H. Yokoyama.
Description. Male (based on holotype, 4.3 mm). Body (Fig. 10) roundish, urosomites 2 and 3 coalesced, eyes absent. Antenna 1 (Fig. 11 A), ratio of peduncular articles 1–3 1: 0.9: 0.4, laterodistal corner of article 1 with 2 penicillate setae, dorsodistal edge of article 2 with penicillate seta; accessory flagellum present, with 2 articles; primary flagellum with 5 articles, distal ends of articles 2–4 each with aesthetasc. Antenna 2 (Fig. 11 B), ratio of peduncular articles 3–5 1: 0.6: 0.3, ventral surface of article 3 with 3 penicillate setae; flagellum with 2 articles. Labrum (Fig, 11 C) triangular, without setae. Mandible (Fig. 11 D, E), molar reduced to several serrate spines; palp article length ratio 1: 3.5: 2.5, article 3 with 2 apical setae. Maxilla 1 (Fig. 11 G, G 1), inner plate with single apical seta, outer plate with various-typed apical setae, palp with 2 apical setae. Maxilla 2 (Fig. 11 H), inner and outer plates with 3 and 4 apical setae, respectively. Maxilliped (Fig. 11 I), inner plate with 2 fine apical setae, outer plate with 3 medial and 1 apical robust setae.
Gnathopod 1 (Fig. 12 A, A 1) small, weakly chelate; coxa rounded posterodistally; basis slender, with 4 setae on posterior margin; merus and carpus setose posteriorly; propodus projected posterodistally, projection with a pair of small robust setae, palm with 3 obtuse processes, distal part of posterior margin setose; dactylus narrow, strongly curved. Gnathopod 2 (Fig. 12 B, B 1) strongly chelate; coxa rounded posterodistally, gill absent; basis broadened distally, curved anteriorly; carpus long, 1.1 times as long as propodus; distal end of propodus with a pair of minute robust setae; tip of dactylus curved. Pereopods 3 and 4 (Fig. 12 C, D) slender, posterodistal corners of coxae square. Pereopod 5 (Fig. 12 E), coxa bilobed; basis rectangular; merus swollen in the middle; carpus 0.9 times as long as propodus. Pereopod 6 (Fig. 12 F), coxa bilobed, anterior lobe small; basis rectangular; merus relatively broadened; carpus 0.9 times as long as propodus. Pereopod 7 (Fig. 12 G), coxa triangular; basis greatly expanded, anterodistal corner protruded, posterior margin serrate, proximal part of medial surface with several setae; merus slender; carpus 0.8 times as long as propodus.
Epimeral plates 2 and 3 (Fig. 13 A) drawn out posteroventrally; ventral margins of plates 2 and 3 with 4 and 5 lateral spines, respectively. Pleopods (Fig. 13 B–D) long, pleopod 3 shortest; peduncles each with 2 coupling hooks and a few plumose setae; outer and inner rami each with 5 and 4 articles, respectively.
Seba latiquinta Holotype, male, 4.3 mm (OMNH-Ar- 7716). A, left antenna 1, dorsal view; B, left antenna 2, lateral view; C, labrum, anterior view; D, right mandible, medial view; E, left mandible, lateral view; F, labium, ventral view; G, left maxilla 1, ventral view; G 1, apical part of outer lobe of left maxilla 1, ventral view; H, left maxilla 2, ventral view; I, right maxilliped, ventral view. Scales: 0.05 mm.
Uropod 1 (Fig. 13 E), peduncle longer than both rami, with 1 dorsal and 2 distal robust setae; outer ramus shorter than inner, both rami bare. Uropod 2 (Fig. 13 F), peduncle shorter than that of uropod 1, with 2 distal robust setae; outer ramus shorter than inner, inner ramus with dorsal robust seta. Uropod 3 (Fig. 13 G), 1 st article of ramus with 1–2 fine setae, 2 nd article minute. Telson (Fig. 13 G) without setae.
Female (based on allotype, 4.1 mm). Gnathopod 1 (Fig. 13 H, H 1) small, weakly chelate; coxa rounded posterodistally; basis slender, with 2 long setae on posterior margin; merus and carpus setose posteriorly; propodus projected posterodistally, projection with a pair of small robust setae, palm almost straight, distal part of posterior margin setose; dactylus narrow, weakly curved. Gnathopod 2 (Fig. 13 I, I 1) strongly chelate; coxa square posterodistally, gill absent; basis slightly curved anteriorly; carpus 0.7 times as long as propodus; distal end of propodus with a pair of minute robust setae; tip of dactylus curved. Pereopods 5 and 6 (Fig. 14 A, B) almost same as those of holotype, but meri slender. Pereopod 7 (Fig. 14 C) almost same as that of holotype, but basis shorter and anterodistal corner not protruded.
Variation of male with growth. Paratype, 2.4 mm (OMNH-Ar- 7722): gnathopod 1 (Fig. 14 D) almost same as that of holotype; pereopods 5 and 6 (Fig. 14 E, F), bases shorter and meri narrower than those of holotype; pereopod 7 (Fig. 14 G), basis shorter than that of holotype, anterodistal corner not protruded. Paratype, 6.0 mm (OMNH-Ar- 7723): gnathopod 1 (Fig. 14 H), palm with 4 obtuse processes; pereopods 5–7 almost same as those of holotype.
Etymology. From the Latin latus (= broad) and quintus (= the fifth), referring to the wide merus of male pereopod 5.
Remarks. This new species is characterized by the male pereopod 5 with expanded merus. Seven Seba species have expanded meri in all of male pereopods 5–7: Seba aloe, S. antarctica Walker, 1906, S. chiltoni, S. gloriosae Ledoyer, 1986, S. hirsuta Ledoyer, 1978, S. saundersi, and S. subantarctica Schellenberg, 1931 (Walker, 1907; Schellenberg, 1931; Karaman, 1971; Griffiths, 1975; Ledoyer, 1978, 1986; Moore, 1987). However, there is no other species having such a wide merus only in pereopod 5.
Habitat. Mud or sandy-mud bottom, 25–31 m deep.
Distribution (Fig. 5). Japan: Kata Bay and Owase Bay in Mie Prefecture.