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

White, Kristine N. & Reimer, James Davis, 2012, Commensal Leucothoidae (Crustacea, Amphipoda) of the Ryukyu Archipelago, Japan. Part III: coral rubble-dwellers, ZooKeys 173, pp. 11-50 : 17-20

Leucothoe akaisen sp. n. Figures 3 4

Type material.

Holotype male, 2.8 mm RUMF-ZC-1854, Sunabe Seawall, Okinawa–jima Island, Okinawa, spur and groove reef (26°19'25"N, 127°44'43"E), among coral rubble, 6-9 m, K.N. White and N.S. White, col., 16 October 2010 (KNWOkinawa12E). Paratype female, 3.4 mm, RUMF-ZC-1855, Yona, Kunigami, Okinawa–jima Island, Okinawa, reef wall (26°45'56"N, 128°11'46"E), among coral rubble, 9 m, K.N. White and N.S. White, col., 23 October 2010 (KNWOkinawa15F).

Type locality.

Sunabe Seawall, Okinawa–jima Island, Okinawa, Japan (26°19'25"N, 127°44'43"E).

Additional material examined.

3 specimens, NSMT-Cr 21995, KNWOkinawa12E; 1 specimen, RUMF-ZC-1856, KNWOkinawa15F; 1 specimen, RUMF-ZC-1857, KNWOkinawa44H; 1 specimen, NSMT-Cr 21996, KNWTokuno4E; 1 specimen, RUMF-ZC-1858, KNWIshigaki4H; 2 specimens, NSMT-Cr 21997, KNWIshigaki2F; 1 specimen, RUMF-ZC-1859, KNWIriomote3C; 4 specimens, RUMF-ZC-1860, KNWYaku3O; 2 specimens, NSMT-Cr 21998, KNWYaku1D; 2 specimens, NSMT-Cr 21999, KNWYaku5J.

Diagnosis (male).

Head anterior margin rounded. Maxilla 1 palp 1-articulate. Gnathopod 1 coxa anterodistal margin produced, subquadrate, with 1 long medial facial seta; dactylus reaching 0.3 × propodus length. Gnathopod 2 propodus mediofacial setal row displaced past midline. Pereopods 5-7 bases broadly expanded. Epimeron 1 with tuft of anteroventral setae. Telson apex rounded.

Description (male).

Head. Anterior margin rounded, anterodistal margin evenly rounded, distal margin straight; ventral cephalic keel anterior margin transverse, anteroventral margin rounded, ventral margin straight; eyes present with more than 10 ommatidia, round. Antenna 1 0.3 × body length, flagellum 5-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum absent. Antenna 2 0.2 × body length, shorter than antenna 1, flagellum 3-articulate. Mandibular palp ratio of articles 1-3 1.0: 2.6: 1.0, article 2 with 5 distal setae, article 3 with two distal setae, incisors weakly dentate; left mandible with 11 raker spines, lacinia mobilis large, weakly toothed; right mandible with 8 raker spines, lacinia mobilis small. Upper lip asymmetrically lobate, anterior margin setose. Lower lip inner lobes fused, setose; outer lobes with large gape, anterior margins setose. Maxilla 1 palp 1-articulate, with 4 distal setae; outer plate with 6 distal robust setae and 2 distal setae. Maxilla 2 inner plate with 9 distal and 1 proximal setae; outer plate with 4 distal and 11 marginal setae. Maxilliped inner plates distal margin rounded with v-shaped indentation, with large and small robust setae; outer plate inner margin smooth, reaching 0.4 × palp article 1, with simple marginal setae, facial setae present; palp article 4 subequal in length with article 3, distally acute.

Pereon. Coxae 1-4 relative widths 1.0: 1.2: 0.7: 1.6. Gnathopod 1 coxa smooth, with tiny marginal setae, anterodistal margin produced, subquadrate, distal margin straight, posterior margin excavate, facial seta present; basis slightly inflated, anterior margin with 1 short and 2 medium setae, posterior margin bare; ischium bare; carpus linear, distal length 10.7 × width, proximal margin smooth, distal margin with 2 setae; propodus straight, palm dentate with 2 large and several small distal setae; dactylus smooth, reaching 0.3 × propodus length. Gnathopod 2 coxa longer than broad, slightly larger than coxa 3, smooth, with tiny marginal setae, anterior margin straight, anterodistally rounded, distal and posterior margins straight, facial setae absent; basis slightly inflated, anterior margin with 4 setae, posterior margin with 1 posterodistal seta; ischium with posterodistal seta; carpus 0.4 × propodus length, curved, distally tapered, anterior margin smooth; propodus with 1 mediofacial setal row displaced past midline, reaching 0.8 × propodus length, with 1 row of submarginal setae, posterior margin smooth, palm convex, with 3 small rounded tubercles; dactylus curved, reaching 0.5 × propodus length, proximal margin smooth, bare, anterior margin distally acute. Pereopod 3 coxa length 1.9 × width, anterodistal corner overriding distal face of coxa 2 and extending below it, smooth, with tiny marginal setae, anterior margin straight, distal margin oblique, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, with tiny marginal setae, anterior margin tapered, distal margin produced, posterior margin excavate, facial setae absent. Pereopods 5-6 coxae, facial setae present, pereopod 7 coxa, facial setae absent. Pereopods 5-7 bases width length ratios 1: 1.2, 1: 1.3, 1: 1.0, posterior margins smooth, setose.

Pleon. Epimeron 1 with anteroventral tuft of setae, epimeron 2 with ventral setae, epimeron 3 bare, posteroventral corner subquadrate, produced. Uropods 1-3 relative lengths 1.0: 0.7: 1.0. Uropod 1 peduncle subequal in length with inner ramus, outer ramus 0.9 × inner ramus length; inner and outer rami each with 2 robust setae. Uropod 2 peduncle subequal in length with inner ramus, outer ramus 0.8 × inner ramus length; inner and outer rami each with 2 robust setae. Uropod 3 peduncle 0.9 × inner ramus length, outer ramus subequal in length with inner ramus; inner ramus with 3 robust setae, outer ramus with 1 robust seta. Telson 2.2 × longer than wide, apex rounded.

Female (sexually dimorphic characters).

Gnathopod 1 basis anterior margin with 5 short and 3 medium setae; carpus distal margin with 3 setae; propodus palm with 4 large and several small distal setae. Gnathopod 2 basis anterior margin with 8 setae; ischium with 2 short anterodistal setae; propodus mediofacial setal row extended proximally with 3 very short setae.

Etymology.

After the Japanese words ‘akai’, meaning ‘red’ and ‘sen’, meaning ‘line’ and referring to the red stripes along the antenna 1 peduncle (pronounced ah-ky-sen).

Ecology.

Host unknown, presumably in sponges in coral rubble.

Relationships.

Leucothoe akaisen sp. n. is similar to Leucothoe trulla White & Reimer, 2012a, Leucothoe commensalis Haswell, 1879, Leucothoe wuriti Thomas & Klebba, 2007, Leucothoe epidemos White & Thomas, 2009, and Leucothoe thula White & Thomas, 2009. The members of this " Leucothoe commensalis group" share a rounded head, long gnathopod 1 dactylus, a displaced gnathopod 2 propodus mediofacial setal row, and wide pereopod 5-7 bases. Leucothoe akaisen sp. n. shares several additional characters with Leucothoe thula , including a maxilla 1 palp with an unclear articulation, a tapered gnathopod 2 carpus, and the gnathopod 2 propodus palm with small tubercles, all of which differ from the other species in this group. Leucothoe akaisen sp. n. is unique in having a longer antenna 1 flagellum, gnathopods 1 and 2 dactylus with proximal setae, and a rounded telson apex.

Remarks.

Leucothoe akaisen sp. n. is very unique in coloration. This species has deep red stripes along the peduncle of antenna 1, a large yellow eye, a yellow “saddleback” pattern, and a deep red dot on coxa 4 (Figure 15D). This species is endemic to the Ryukyus Archipelago, having been collected throughout the island chain. The color pattern of this species resembles that of an undescribed species collected in Guam from polychaete worm tubes (Thomas, pers.com.).

Distribution.

East China Sea: Ishigaki–jima Island, Iriomote–jima Island, Okinawa–jima Island (both Okinawa), Tokunoshima Island, Yakushima Island (both Kagoshima), Japan.