Seba latiquinta, Ariyama, Hiroyuki, 2009

Ariyama, Hiroyuki, 2009, Four species of the genus Seba from Japan, with descriptions of two new species (Crustacea: Amphipoda: Sebidae), Zootaxa 2159, pp. 44-68 : 55-61

Seba latiquinta sp. nov.

( 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. 11A), 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. 11B), 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, 11C) triangular, without setae. Mandible (Fig. 11D, 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. 11G, G1), inner plate with single apical seta, outer plate with various-typed apical setae, palp with 2 apical setae. Maxilla 2 (Fig. 11H), inner and outer plates with 3 and 4 apical setae, respectively. Maxilliped (Fig. 11I), inner plate with 2 fine apical setae, outer plate with 3 medial and 1 apical robust setae.

Gnathopod 1 ( Fig. 12 A, A1) 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, B1) 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; G1, 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), 1st article of ramus with 1–2 fine setae, 2nd article minute. Telson ( Fig. 13 G) without setae.

Female (based on allotype, 4.1 mm). Gnathopod 1 ( Fig. 13 H, H1) 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, I1) 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.

Figures

FIGURE 5. Distributions of Seba species dealt in the present study.

FIGURE 10. Seba latiquinta sp. nov. Holotype, male, 4.3 mm (OMNH-Ar- 7716), habitus, left lateral view. Scale: 0.5 mm.

FIGURE 12. Seba latiquinta sp. nov. Holotype, male, 4.3 mm (OMNH-Ar- 7716). A, left gnathopod 1, lateral view; A 1, palm of left gnathopod 1, lateral view; B, left gnathopod 2, lateral view; B 1, apical part of left gnathopod 2, lateral view, setae omitted; C – G, left pereopods 3 – 7, lateral views. Scales: 0.05 mm.

FIGURE 13. Seba latiquinta sp. nov. A – G, holotype, male, 4.3 mm (OMNH-Ar- 7716); H, H 1, I, I 1, allotype, female, 4.1 mm (OMNH-Ar- 7717). A, right epimeral plates 1 – 3, lateral view; B – D, left pleopods 1 – 3, posterior views; E, F, left uropods 1, 2, lateral views; G, uropods 3 and telson, dorsal view; H, left gnathopod 1, lateral view; H 1, palm of left gnathopod 1, lateral view; I, left gnathopod 2, lateral view; I 1, apical part of left gnathopod 2, lateral view, setae omitted. Scales: 0.05 mm.

FIGURE 14. Seba latiquinta sp. nov. A – C, allotype, female, 4.1 mm (OMNH-Ar- 7717); D – G, paratype, male, 2.4 mm (OMNH-Ar- 7722); H, paratype, male, 6.0 mm (OMNH-Ar- 7723). A – C, E – G, left pereopods 5 – 7, lateral views; D, H, propodi and dactyli of left gnathopods 1, lateral views, setae omitted. Scales: 0.05 mm.