Leucothoe enko, 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 : 28-31

Leucothoe enko sp. n. Figures 9, 10

Type material.

Holotype male, 1.6 mm RUMF-ZC-1850, Omonawa, Tokunoshima Island, Kagoshima, reef wall (27°53'29"N, 128°56'10"E), among coral rubble, 21 m, K.N. White and N.S. White, col., 21 September 2010 (KNWTokuno3B). Paratype female, 1.7 mm, RUMF-ZC-1851, Toguchi Beach, Okinawa–jima Island, Okinawa, patch reef (26°21'47"N, 127°44'12"E), among coral rubble, 1-2 m, K.N. White and N.S. White, col., 20 October 2010 (KNWOkinawa14C).

Type locality.

Omonawa, Tokunoshima Island, Kagoshima, Japan (27°53'29"N, 128°56'10"E).

Additional material examined.

1 specimen, RUMF-ZC-1852, KNWTokuno3B; 4 specimens, NSMT-Cr 21993, KNWOkinawa24C; 1 specimen, RUMF-ZC-1853, KNWOkinawa24C; 1 specimen, NSMT-Cr 21994, KNWOkinawa71B.

Diagnosis (male).

Head anterior margin oblique, produced, distal margin excavate with rounded projection. Maxilla 1 palp 1-articulate, margins constricted. Gnathopod 1 propodus proximally inflated: dactylus reaching 0.1 × propodus length. Gnathopod 2 basis distally expanded, stout; propodus palm concave with 6 large tubercles. Pereopods 5-7 bases narrowly expanded, posterior margins serrate.

Description (male).

Head. Anterior margin oblique, produced, anterodistal margin rounded, distal margin excavate with rounded projection; ventral cephalic keel anterior produced, excavate; anteroventral margin quadrate, ventral margin excavate; eyes present with more than 10 ommatidia, round. Antenna 1 0.3 × body length, flagellum 6-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum absent. Antenna 2 0.3 × body length, subequal in length with antenna 1, flagellum 4-articulate. Mandibular palp ratio of articles 1-3 1.0: 2.4: 0.6, article 2 with 3 distal setae, article 3 with two distal setae, incisors weakly dentate; left mandible with 5 raker spines, lacinia mobilis large, weakly toothed; right mandible with 5 raker spines, lacinia mobilis small, weakly toothed. Upper lip asymmetrically lobate, anterior margin weakly setose. Lower lip inner lobes fused, setose; outer lobes with moderate gape, anterior margins setose. Maxilla 1 palp 1-articulate, margins constricted with 3 distal slender setae; outer plate with 5 distal robust setae. Maxilla 2 inner plate with 4 distal slender setae outer plate with 3 distal slender setae. Maxilliped inner plates distal margin rounded with v-shaped indentation, with short simple robust setae; outer plate inner margin smooth, reaching 0.2 × 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: 1.1: 0.9:1.0. Gnathopod 1 coxa smooth, bare, anterodistal margin produced, rounded, distal margin straight, posterior margin excavate, facial setae absent; basis distally expanded, anterior and posterior margins bare; ischium bare; carpus linear, distal length 9.1 × width, proximal margin dentate, distal margin with 4 long setae; propodus proximally inflated, palm dentate with 4 distal setae; dactylus smooth, reaching 0.1 × propodus length. Gnathopod 2 coxa broader than long, subequal in size with coxa 3, smooth, bare, anterior margin straight, anterodistally rounded, distal margin rounded, posterior margin straight, facial setae absent; basis distally expanded, stout, anterior margin with 3 setae, posterior margin bare; ischium bare; carpus 0.5 × propodus length, curved, distally tapered, anterior margin smooth; propodus with 1 mediofacial setal row above midline, reaching 0.7 × propodus length, without submarginal setae, posterior margin smooth, palm concave with 6 major and 3 minor tubercles; dactylus curved, proximal margin smooth, bare, anterior margin distally acute, reaching 0.6 × propodus length. Pereopod 3 coxa length 1.2 × width, anterodistal corner overriding distal face of coxa 2, not extending below it, smooth, bare, anterior margin straight, distal margin slightly rounded, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, bare, anterior margin straight, distal margin rounded, posterior margin straight, facial setae absent. Pereopods 5-7 coxae facial setae absent; bases width length ratios 1: 2.2, 1: 1.9, 1: 1.8, posterior margins serrate, bare.

Pleon. Epimera 1-2 with ventral setae, epimeron 3 bare, posteroventral corner subquadrate. Uropods 1-3 relative lengths 1.0: 0.6: 0.9. Uropods 1-2 peduncles 0.8 × inner rami lengths, outer rami 0.6 × inner rami lengths. Uropod 1 inner ramus with 2 robust setae, outer ramus with 1 robust seta. Uropod 2 inner and outer rami each with 1 robust seta. Uropod 3 peduncle and inner ramus 0.7 × inner ramus length; inner and outer rami bare. Telson 1.8 × longer than wide, apex rounded.

Female (sexually dimorphic characters).

Gnathopod 1 basis anterior margin with 3 short setae; carpus distal margin with 7 long setae. Gnathopod 2 basis anterior margin with 3 distal tubercules, with 3 short and 2 medium setae, posterior margin with 1 short seta; propodus with 2 rows of submarginal setae, palm 5 major tubercles; dactylus reaching 0.7 × propodus length.

Etymology.

After the Japanese word ‘enko’, meaning ‘arc’ and referring to the concave gnathopod 2 propodus palm (pronounced en-koh).

Ecology.

Host unknown, presumably living in sponges in coral rubble.

Relationships.

Leucothoe enko sp. n. fits into a distinct group of small species sharing a proximally inflated gnathopod 1 propodus and very strong dentition on the propodus palm of gnathopod 2. These species include Leucothoe adelphe White & Thomas, 2009, Leucothoe micronesiae Barnard, 1965, and Leucothoe minuscula Schellenberg, 1938. Leucothoe enko sp. n. differs from these species in having the maxilla 1 palp 1-articulate with margins constricted, a proximally dentate gnathopod 1 carpus and propodus, posteriorly serrate pereopods 5-7 bases, and telson with a rounded apex.

Remarks.

Leucothoe enko sp. n. is deep yellow in color with a small red eye (Figure 15C). This species is endemic to the central Ryukyu Islands. Upon further examination, this group of species may prove to be a part of a cryptic species complex, with different species inhabiting similar niches at different locations.

Distribution.

East China Sea: Okinawa–jima Island (Okinawa), Okinoerabu–jima Island and Tokunoshima Island (both Kagoshima), Japan.