Paranamixis Schellenberg, 1938

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 : 34-38

Paranamixis Schellenberg, 1938 Figures 13, 14

Paranamixis misakiensis Thomas, 1997: 89-91, fig. 26.

Material examined.

Anamorph male, 3.5 mm RUMF-ZC-1875, Haruta, Yakushima Island, Kagoshima, reef wall (30°18'12"N, 130°39'28"E), among coral rubble, 10 m, K.N. White and N.S. White, col., 27 May 2011 (KNWYaku4C).

Diagnosis (Anamorph male).

Head anterior margin oblique, anterodistal margin oblique with notch; ventral cephalic keel anterior margin oblique with projection and excavation. Antenna 2 longer than antenna 1. Maxilliped inner plates fused with apical notch. Gnathopod 1 coxa anterodistal margin subtriangular, bi-cuspidate. Gnathopod 2 coxa broader than long, greatly enlarged, distal margin with anterior and posterior cusps; basis anterior margin with distal serrate ridge; carpus distally tapered, anterior margin dentate; dactylus proximal margin dentate with 2 plumose setae. Telson apex rounded.

Description (Anamorph male).

Head. Anterior margin oblique, anterodistal margin oblique with notch, distal margin rounded; ventral cephalic keel anterior margin oblique with projection and excavation, anteroventral margin quadrate, produced, ventral margin oblique; eyes present with more than 10 ommatidia, round. Antenna 1 0.3 × body length, flagellum 7-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum 1-articulate. Antenna 2 0.4 × body length, longer than antenna 1, flagellum 3-articulate. Mouthparts reduced. Maxilliped inner plates fused with apical notch; outer plate inner margin smooth, reaching 0.1 × palp article 1, bare; palp 4-articulate, article 4 elongate, distally acute.

Pereon. Coxae 1-4 relative widths 1.0: 2.9: 1.7: 2.0. Gnathopod 1 absent, coxa smooth, with tiny marginal setae, anterodistal margin produced, subtriangular, bi-cuspidate, distal margin oblique, posterior margin straight, facial setae absent. Gnathopod 2 coxa broader than long, greatly enlarged, smooth, bare, anterior margin rounded, anterodistally rounded, distal margin rounded with anterior and posterior cusps, posterior margin rounded, facial setae absent; basis distally expanded, anterior margin with distal serrate ridge and 7 short setae, posterior margin with 1 posterodistal seta; ischium bare; carpus 0.8 × propodus length, curved, distally tapered, anterior margin dentate; propodus with 1 mediofacial setal row above midline, reaching 0.5 × propodus length, with 1 row of submarginal setae, posterior margin serrate, palm convex with 3 major and many small tubercles; dactylus curved, proximal margin dentate with 2 plumose setae, anterior margin distally obtuse, reaching 0.3 × propodus length. Pereopod 3 coxa length 1.4 × width, anterodistal corner overriding distal face of coxa 2, not extending below it, smooth, bare, anterior margin straight, distal margin straight with mid-distal cusp, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, bare, anterior margin straight, distal margin rounded with anterior and mid-distal cusps, posterior margin excavate, facial setae absent. Pereopods 5-7 coxae facial setae absent; bases width length ratios 1: 1.3, 1: 1.3, 1: 1.4, posterior margins smooth, setose.

Pleon. Epimera 1-3 bare; epimeron 3 posteroventral corner quadrate. Uropods 1-3 relative lengths 1.0: 0.8: 0.9. Uropod 1 peduncle 0.9 × inner ramus length, outer ramus 0.5 × inner ramus length; inner ramus with 4 robust setae, outer ramus with 2 robust setae. Uropod 2 peduncle 0.8 × inner ramus length, outer ramus 0.6 × inner ramus length; inner and outer rami each with 3 robust setae. Uropod 3 peduncle 1.3 × inner ramus length, outer ramus 0.7 × inner ramus length; inner ramus bare, outer ramus with one robust seta. Telson 1.1 × longer than wide, apex rounded.

Leucomorph (juvenile and sexually dimorphic characters).

Unknown.

Ecology.

Host unknown, presumably in sponges in coral rubble.

Relationships.

Paranamixis misakiensis appears most closely related to Paranamixis thomasi in the cuspate, oblique anterodistal head margin, excavate anterior ventral cephalic keel margin, apically cleft maxilliped inner plates, and enlarged gnathopod 2 coxa. Paranamixis misakiensis differs from Paranamixis thomasi in the following: ventral cephalic keel anterior margin with mid-distal projection; gnathopod 2 basis anterior margin with a much larger serrate ridge, propodus with one mediofacial setal row, dactylus proximal margin and dentate. Paranamixis denticulus Kim and Kim, 1991 and Paranamixis aberro Hirayama 1983 also share the oblique, cuspate anterior head margin, but differ in many other aspects.

Remarks.

Anamorph males of Paranamixis misakiensis is white in color with pink stripes along pereonite edges (Figure 15G). This species was collected from Yakushima Island, extending its known range approximately 1000 kilometers. The specimen from Yakushima closely agrees with Thomas’ 1997 description, differing slightly in the ventral cephalic keel, which is excavate with a mid-distal projection, versus excavate in Thomas’ 1997 material.

Distribution.

East China Sea: Yakushima Island (Kagoshima), Japan. Pacific Ocean: Misaki, Miura Peninsula (Kanagawa), Japan.