Seba ekepuu J.L. Barnard, 1970

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 : 51-55

Seba ekepuu J.L. Barnard, 1970

( Figs 6–9 )

Seba ekepuu J.L. Barnard, 1970: 246 , figs 162–163 (type locality: Kawela Bay, Oahu, Hawaii).— J.L. Barnard, 1971: 117, fig. 61.— Ledoyer, 1979: 130, fig. 83.— Ledoyer, 1986: 946, fig. 372A.

Material examined. Three males, 1.5, 1.4, 1.4 mm (OMNH-Ar-7705–7707), 5 females, 1.6, 1.6, 1.6, 1.6, 1.5 mm (OMNH-Ar-7708–7712), and 2 ovigerous females, 1.5, 1.4 mm (OMNH-Ar-7713, 7714), Tagurazaki, Wakayama City in Wakayama Prefecture, uppermost part of sublittoral zone, coarse sand bottom, using decantation method, 30 June 2007, coll. H. Ariyama. One male, 1.1 mm (OMNH-Ar-7715), Nezumi Island, Chita Town in Aichi Prefecture, 4 m deep, shell bottom, using decantation method, 5 August, 2001, coll. H. Ariyama.

Description. Based on male "2", 1.4 mm (OMNH-Ar-7706), female "1", 1.6 mm (OMNH-Ar-7707) for body and female gnathopods and pereopods, and female "2", 1.6 mm (OMNH-Ar-7708) for epimeral plates. Body ( Fig. 6 ) small, relatively slender, urosomites 2 and 3 coalesced, eyes absent. Antenna 1 ( Fig. 7 A), ratio of peduncular articles 1–3 1:0.8:0.4, ventrodistal corner of article 1 with 2 penicillate setae, dorsodistal and ventrodistal edges of article 2 each with penicillate seta, dorsodistal and ventrodistal corners of article 3 with penicillate seta and aesthetasc, respectively; accessory flagellum present, with 2 articles; primary flagellum with 4 articles, distal ends of articles 1 and 2 with 2 and 1 aesthetascs, respectively. Antenna 2 ( Fig. 7 B), ratio of peduncular articles 3–5 1:0.8:0.1, distal edge of articles 3 and 4 each with 2 penicillate setae; flagellum with 2 articles. Labrum (Fig, 7C) roundish triangular, without setae. Mandible ( Fig. 7 C), molar indistinct; palp article length ratio 1:3.1:1.1, article 2 with 1–2 short setae, article 3 with single apical seta. Maxilla 1 ( Fig. 7 E, E1), inner plate bare, outer plate with various-shaped apical setae and several fine medial setae, palp with 2 apical setae. Maxilla 2 ( Fig. 7 F), inner and outer plates with 2 and 3 apical setae, respectively. Maxilliped ( Fig. 7 G), inner plate with 3 apical setae, outer plate with 2 medial and 1 apical setae; palp weakly setose.

Gnathopod 1 ( Fig. 8 A, A1) small, chelate; coxa rounded posterodistally; basis slender, broadened distally, with seta on posterodistal corner; ischium, merus and carpus with 1, 2 and 1 pectinate setae posteriorly; propodus projected posterodistally, tip of projection with a pair of minute robust setae, palm smooth, posterior margin setose in the middle; dactylus narrow, weakly curved. Gnathopod 2 ( Fig. 8 B) slender, strongly chelate; coxa square posterodistally, gill absent; basis almost straight; carpus 0.4 times as long as propodus; propodus and dactylus long. Pereopods 3 and 4 ( Fig. 8 C, D), posterodistal corners of coxae roundish square; bases widened distally. Pereopod 5 ( Fig. 8 E), coxa bilobed; basis rectangular, but narrowed distally; merus narrow; carpus 0.7 times as long as propodus. Pereopod 6 ( Fig. 8 F), coxa bilobed, anterior lobe small; basis ovoid, broadened proximally, posterior margin serrate; merus narrow; carpus 0.7 times as long as propodus. Pereopod 7 ( Fig. 8 G), coxa ovoid; basis widely expanded, broadened proximally, anterior margin with several small robust setae, posterior margin serrate; merus narrow; carpus 0.6 times as long as propodus.

Epimeral plates ( Fig. 9 I), posteroventral corner rounded in plate 2 and pointed minutely in plate 3; ventral margin of plate 3 with short seta. Pleopods ( Fig. 9 A–C), peduncles each with 2 coupling hooks but without setae; outer and inner rami each with 3 and 2 articles, respectively, plumose setae of rami long. Uropod 1 ( Fig. 9 D), peduncle much shorter than both rami, with 2 distal setae; outer ramus shorter than inner, both rami curved dorsally, bare. Uropod 2 ( Fig. 9 E), peduncle longer than that of uropod 1, with distal robust seta; outer ramus subequal length to inner, both rami bare, but proximal margin of inner ramus pectinate. Uropod 3 ( Fig. 9 F), peduncle with short distal seta; 1st article of ramus with 2 short distal setae, 2nd article relatively stout. Telson ( Fig. 9 F) roundish triangular, with a pair of distal setae.

Female gnathopods 1 and 2 ( Fig. 9 G, H) and pereopods 5–7 almost same as those of male except for oostegites.

Remarks. This species has the proximally broadened bases of pereopods 5–7, and the peduncle of uropod 1 shorter than that of uropod 2. The present specimens share these characters with Seba ekepuu in J.L. Barnard (1970) and Ledoyer (1979, 1986). In the other characters, the specimens also agree with them; however, numbers of setae in maxilla 2 is different from J.L. Barnard (1970) (inner plate: 3, outer plate: 4). J.L. Barnard (1970) and Ledoyer (1979, 1986) described based on the materials of sex unknown, female and male?, respectively. In the present study, I described both of the correct male and female of this species, and revealed that the sexual dimorphism is indistinct.

Habitat. Coarse sand or shell bottom, 0–4 m deep (present study); a brown alga Sargassum , algae, rocks, corals, intertidal ( J.L. Barnard, 1970); sand, gravel, a red alga Melobesia , 3–36 m deep ( Ledoyer, 1979).

Distribution ( Fig. 5 ). Japan: Tagurazaki in Wakayama Prefecture, Nezumi Island in Aichi Prefecture; Hawaii ( J.L. Barnard, 1970, 1971); Madagascar ( Ledoyer, 1979, 1986).

Figures

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

FIGURE 6. Seba ekepuu J. L. Barnard, 1970. Female " 1 ", 1.6 mm (OMNH-Ar- 7708), habitus, left lateral view. Scale: 0.25 mm.

FIGURE 7. Seba ekepuu J. L. Barnard, 1970. Male " 2 ", 1.4 mm (OMNH-Ar- 7706). A, B, left antennae 1, 2, medial views; C, labrum and mandibles, anteromedial view; D, labium, ventral view; E, right maxilla 1, ventral view; E 1, apical part of outer plate of right maxilla 1, ventral view; F, left maxilla 2, ventral view; G, right maxilliped, dorsal view. Scales: 0.025 mm.

FIGURE 8. Seba ekepuu J. L. Barnard, 1970. Male " 2 ", 1.4 mm (OMNH-Ar- 7706). A, left gnathopod 1, lateral view; A 1, palm of left gnathopod 1, lateral view; B, left gnathopod 2, lateral view; C – G, left pereopods 3 – 7, lateral views (gills on pereopods 3 and 6 lost). Scales: 0.025 mm.

FIGURE 9. Seba ekepuu J. L. Barnard, 1970. A – F, male " 2 ", 1.4 mm (OMNH-Ar- 7706); G, H, female " 1 ", 1.6 mm (OMNH-Ar- 7708); I, female " 2 ", 1.6 mm (OMNH-Ar- 7709). A, B, left pleopods 1, 2, anterior views; C, left pleopod 3, posterior view; D, left uropod 1, dorsolateral view; E, left uropod 2, dorsomedial view; F, uropods 3 and telson, dorsal view; G, H, left gnathopods 1, 2, lateral views; I, left epimeral plates 1 – 3, lateral view. Scales: 0.025 mm.