Leucothoe elegans, White, Kristine N. & Reimer, James Davis, 2012

White, Kristine N. & Reimer, James Davis, 2012, Commensal Leucothoidae (Crustacea, Amphipoda) of the Ryukyu Archipelago, Japan. Part I: ascidian-dwellers, ZooKeys 163, pp. 13-55 : 20-24

Leucothoe elegans sp. n. Figs 56

Type material.

Holotype male, 4.5 mm, RUMF-ZC-1658, Isso, Yakushima Island patch reef (30°27'29"N, 130°29'22"E), in grey-purple hard sponge, 10-12 m, K.N. White, col., 27 May 2011 (KNWYaku3A). Paratype female, 5.7 mm, RUMF-ZC-1659, same station data as holotype.

Type locality. Isso, Yakushima Island, Japan (30°27'29"N, 130°29'22"E).

Additional Material Examined.

8 specimens, NSMT-Cr21815, KNWYaku3B; 4 specimens, RUMF-ZC-1660, KNWYaku3L; 3 specimens, RUMF-ZC-1661, KNWYaku5C; 3 specimens, RUMF-ZC-1662, KNWOkinawa54A; 16 specimens, NSMT- Cr 21816, KNWOkinawa54I; 2 specimens, RUMF-ZC-1699, KNWOkinawa54I.

Diagnosis (male). Mandibular palp article 2 robust, with 4 setae. Right mandible lacinia mobilis distal margin with 3 rows of dentition. Maxilliped outer plate inner margin tuberculate. Eye large, covering most head. Gnathopod 1 basis proximally widened; carpus elongate. Gnathopod 2 propodus with one submarginal row of robust setae; dactylus proximal margin with 2 setae, distal margin with spine; epimeron 3 posteroventral margin with small sinus.

Description (male).

Head. Anterior margin truncate, anterodistal margin evenly rounded; ventral cephalic keel anterior margin transverse, anteroventral margin rounded, ventral margin straight; eyes with more than 10 ommatidia, large, round. Antenna 1 0.2 × body length, flagellum 6-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum 2-articulate. Antenna 2 0.2 × body length, subequal in length with antenna 1, flagellum 4-articulate. Mandibular palp ratio of articles 1-3 1.0: 3.5: 1.6, article 2 robust with 4 setae, article 3 with 2 distal setae, incisors strongly dentate; left mandible with 12 raker spines, lacinia mobilis large, strongly toothed; right mandible with 12 raker spines, lacinia mobilis small, weakly dentate, with 3 rows of dentition. Upper lip asymmetrically lobate, anterior margin bare. Lower lip inner lobes fused, setose, with facial setae; outer lobes with moderate gape, anterior margins setose. Maxilla 1 palp 1-articulate with 3 distal setae; outer plate with 6 distal robust setae and 5 distal slender setae. Maxilla 2 inner plate with 3 robust distal setae and 5 slender distal setae; outer plate with 4 robust distal marginal setae and 21 marginal setae. Maxilliped inner plates distal margin with arc-shaped indentation, with short robust setae and long plumose setae; outer plate inner margin tuberculate, reaching 0.2 × palp article 1, inner plate plumose marginal setae; palp article 4 subequal in length with article 3, distally acute.

Pereon. Coxae 1-4 relative widths 1.0: 1.6: 1.4: 1.7. Gnathopod 1 coxa smooth, with tiny marginal setae, anterodistal margin produced, subquadrate with cusp, distal margin rounded, posteroventral margin narrowly rounded, facial setae absent; basis centrally expanded, anterior margin with 2 short setae, posterior margin with 2 medium setae; ischium bare; carpus linear, length 14.2 × width, proximal margin dentate, distal margin with 3 short setae; propodus curved, palm dentate with 6 distal setae; dactylus with linear striation and 1 short seta, reaching 0.2 × propodus length. Gnathopod 2 coxa broader than long, subequal to coxa 3, smooth, with tiny marginal setae, anterior margin expanded anteriorly with cusp, anterodistally subquadrate, distal margin straight, posterior margin straight, facial setae absent; basis distally expanded, anterior margin with 6 short setae, posterior margin bare; ischium with 3 distal setae and 1 posterodistal seta; carpus 0.3 × propodus length, curved, distally tapered, anterior margin dentate; propodus with 1 mediofacial setal row displaced to palm, reaching 0.7 × propodus length, with 1 row of robust submarginal setae, posterior margin smooth, palm convex with 4 major tubercles; dactylus curved, proximal margin smooth with 2 setae, distal margin with 1 tooth, anterior margin distally acute, reaching 0.7 × propodus length. Pereopod 3 coxa length 1.1 × width, anterodistal corner overriding distal face of coxa 2, extending below it, smooth, with tiny marginal setae, anterior margin expanded, distal margin slightly convex with cusps, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, with tiny marginal setae, anterior margin produced with cusp, distal margin evenly rounded, posterior margin excavate, facial setae absent. Pereopods 5-7 coxae facial setae absent; bases oval, width length ratios 1: 1.3, 1: 1.4, 1: 1.4; posterior margins serrate, setose.

Pleon. Epimera 1-2 with ventral setae, epimeron 3 bare; epimeron 3 posteroventral corner with small sinus, subquadrate. Uropods 1-3 relative lengths 1.0: 0.7: 0.7; inner and outer rami lined with short marginal setae. Uropod 1 peduncle and outer ramus subequal in length with inner ramus; inner and outer rami each with 3 robust setae. Uropod 2 peduncle 0.9 × inner ramus length; outer ramus 0.8 × inner ramus length; inner and outer rami each with 2 robust setae. Uropod 3 peduncle 1.5 × inner ramus length; outer ramus 0.9 × inner ramus length; inner and outer rami each with 2 robust setae. Telson 1.9 × longer than wide, without facial or marginal setae, apex very weakly tridentate.

Female (sexually dimorphic characters).

Gnathopod 1 basis anterior margin with 3 short setae, posterior margin with 15 medium setae; ischium with 1 posterodistal seta; carpus distal margin with 4 short setae; propodus palm with 9 distal setae. Gnathopod 2 propodus with longer robust submarginal setae.

Etymology.

After the Latin ‘elegans’, meaning tasteful, choice, fine, and referring to the elegant, elongate gnathopod 1 of males and females of this species.

Ecology.

In branchial chamber of solitary ascidian, Rhopalaea circula (Fig. 18F); grey/purple hard sponge; dark red chimney sponge; orange flame sponge; purple brown soft sponge; and orange stubby sponge.

Relationships.

Leucothoe elegans is similar to Leucothoe germanalcyone Hirayama, 1992 in having an enlarged eye; similar to Leucothoe flammosa Thomas and Klebba, 2007 and Leucothoe uschakovi Gurjanova, 1951 in having an elongate gnathopod 1 with a centrally widened basis; and similar to Leucothoe nagatai in having short antennae, narrow pereopod 5-7 bases, and a sinuous epimeron 3. Leucothoe elegans differs from these species in having a dentate right mandible lacinia mobilis, female gnathopod 1 with many posterior setae, and gnathopod 2 propodus with submarginal row of robust setae.

Remarks.

Leucothoe elegans is translucent ivory in color (Fig. 17C). This species has only been collected on Yakushima Island and from Shioya Bay, on the east coast of Okinawa–jima Island, Okinawa.

Distribution.

East China Sea: Okinawa–jima Island, Okinawa and Yakushima Island, Kagoshima, Japan.