Paranamixis thomasi, 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 : 37-41

Paranamixis thomasi sp. n. Figs 1516

Type material.

Holotype male, 2.6 mm, RUMF-ZC-1690, Sunabe Seawall reef (26°19'25"N, 127°44'43"E), coral rubble, 7-10 m, K.N. White and N.S. White col., 5 October 2010 (KNWOkinawa12D). Paratype male, 2.6 mm, RUMF-ZC-1692, Toguchi Beach patch reef (26°21'47"N, 127°44'12"E), coral rubble, 1-3 m, K.N. White and N.S. White col., 3 February 2011 (KNWOkinawa28B). Paratype female, 2.3 mm, RUMF-ZC-1691, same station data as holotype.

Type locality.

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

Additional Material Examined.

2 anamorphs, 15 leucomorphs, RUMF-ZC-1693, KNWOkino1B; 2 anamorphs, 19 leucomorphs, NSMT - Cr21835, KNWJap10-9-8A; 1 anamorph, 3 leucomorphs, RUMF-ZC-1694, KNWOkinawa20A; 1 anamorph, 12 leucomorphs, NSMT- Cr21836, KNWOkinawa14G; 1 leucomorph, RUMF-ZC-1700, KNWOkinawa14G; 14 leucomorphs, RUMF-ZC-1695, KNWTokuno4F; 1 anamorph, RUMF-ZC-1696, KNWOkinawa36D; 1 anamorph, RUMF-ZC-1697, KNWOkinawa38D; 1 anamorph, NSMT - Cr21837, KNWIshigaki4J; 1 anamorph, RUMF-ZC-1694, KNWOkinawa47F.

Diagnosis (male).

Terminal anamorph head with lateral ridge, anterodistal margin quadrate with cusp. Maxilliped inner plates with small cleft. Coxa 1 anterodistally subtriangular, bi-cuspidate; gnathopod 1 absent. Gnathopod 2 coxa anterior margin expanded with cusp; basis with anterodistal serrate ridge; propodus with 2 mediofacial setal rows, posterior margin serrate; dactylus proximal margin with 1 tubercle and 2 plumose setae. Sub-terminal female Head. Anterior margin truncate. Mandibular palp 1-articulate. Gnathopod 1 carpus terminal ornamentation consisting of 2 serrate blades; propodus palm with 7 sets of 3 setae. Gnathopod 2 propodus palm with 6 major tubercles.

Description (Anamorph male).

Head with lateral ridge. Anterior margin oblique, anterodistal margin quadrate with cusp; ventral cephalic keel anterior margin excavate, anteroventral margin subquadrate, ventral margin excavate; eyes with more than 10 ommatidia, round. Antenna 1 0.4 × body length, flagellum 7-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum absent, aesthetascs present. Antenna 2 0.4 × body length, subequal in length with antenna 1, flagellum 3-articulate. Mouthparts reduced. Maxilliped inner plates with small cleft, bare; 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: 2.5: 1.6: 2.1. Gnathopod 1 coxa smooth, bare, anterodistal margin produced, subtriangular, bi-cuspidate, distal margin oblique, posterior margin straight, facial setae absent. Gnathopod 1 absent. Gnathopod 2 coxa broader than long, greatly enlarged, smooth, with tiny marginal setae, anterior margin expanded with cusp, anterodistally rounded, distal margin evenly rounded, posterior margin straight, facial setae absent; basis anterodistally expanded, with anterodistal serrate ridge, anterior margin 3 short setae, posterior margin bare; ischium bare; carpus 0.7 × propodus length, curved, distally tapered, anterior margin smooth; propodus with 2 mediofacial setal rows, primary mediofacial setal row above midline, reaching 0.4 × propodus length, secondary mediofacial setal row with 4 setae, with 1 row of submarginal setae, posterior margin serrate, palm convex with 3 major and several minor tubercles; dactylus curved, proximal margin with 1 tubercle and 2 plumose setae, anterior margin distally acute, reaching 0.4 × propodus length. Pereopod 3 coxa length 1.3 × width, anterodistal corner overriding distal face of coxa 2, not extending below it, smooth, with tiny marginal setae, anterior margin expanded, distal margin slightly convex with cusp, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, with tiny marginal setae, anterior margin produced, distal margin evenly rounded, posterior margin excavate, facial setae absent. Pereopods 5-7 coxae facial setae absent; bases width length ratios 1: 1.4, 1: 1.5, 1: 1.5; posterior margins smooth, setose.

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

Leucomorph (juvenile and sexually dimorphic characters).

Head. Anterior margin truncate, anterodistal margin subquadrate; ventral cephalic keel anterior margin truncate, anteroventral margin produced, ventral margin straight; eyes with more than 10 ommatidia, round. Antenna 1 0.3 × body length, flagellum 8-articulate. Antenna 2 0.3 × body length, shorter than antenna 1, flagellum 3-articulate. Mandibles lacking molars, palp 1-articulate with 2 distal setae, incisors weakly dentate, left mandible with 5 raker spines, lacinia mobilis large; right mandible with 5 raker spines, lacinia mobilis small. Upper lip asymmetrically lobate, anterior margin setose. Lower lip inner lobes fused, bare; outer lobes with small gape, anterior margins setose. Maxilla 1 palp 1-articulate with 3 distal setae; outer plate with 2 distal robust setae, 6 distal setae. Maxilla 2 inner plate with 2 distal setae; outer plate with 2 distal setae, facial setae present. Maxilliped inner plates fused, distal margin with v-shaped indentation, with short robust setae; outer plate inner margin smooth, reaching 0.2 × palp article 1, with 4 simple marginal setae; palp 4-articulate, article 4 subequal in length with article 3, distally acute.

Pereon. Coxae 1-4 relative widths 1.0: 1.4: 0.9: 1.4. Gnathopod 1 coxa smooth, bare, anterodistal margin rounded, distal margin oblique, posterior margin straight, facial setae absent; basis linear, anterior and posterior margins bare; ischium bare; carpus linear, length 16 × width, proximal margin smooth, with terminal serrate blades and bulbous tip, distal margin with 1 short seta; propodus proximally inflated, palm smooth with 7 sets of 3 proximal setae; dactylus smooth, with large proximal spine, reaching 0.1 × propodus length. Gnathopod 2 coxa equally as long as broad, slightly larger than coxa 3, smooth, with tiny marginal setae, anterior margin expanded, anterodistally subquadrate with cusp, distal margin straight, posterior margin tapered with posteroventral cusp; basis distally expanded, with 4 small anterodistal tubercles; ischium with 1 posterodistal seta; carpus 0.4 × propodus length, straight, distally tapered, anterior margin smooth; propodus with 1 mediofacial setal row displaced to midline, reaching 0.4 × propodus length, with 1 row of submarginal setae, posterior margin smooth, palm subtriangular with 6 major tubercles; dactylus proximal margin smooth, setose, anterior margin distally acute, reaching 0.3 × propodus length. Pereopod 3 coxa length 1.8 × width, smooth, with tiny marginal setae, anterior margin straight, distal margin slightly convex, posterior margin straight, facial setae absent. Pereopod 4 coxa smooth, with tiny marginal setae, anterior margin straight, distal margin evenly rounded, posterior margin tapered, facial setae absent. Pereopods 5-7 coxae facial setae absent; bases width length ratios 1: 1.2, 1: 1.1, 1: 1.2, posterior margins smooth, setose.

Pleon. Epimera 1-2 with ventral setae; epimeron 3 bare, posteroventral corner subquadrate. Uropods 1-3 relative lengths 1.0: 0.7: 1.3. Uropod 1 peduncle 0.6 × inner ramus; outer ramus 0.9 × inner ramus; inner and outer rami each with 3 robust setae. Uropod 2 peduncle and outer ramus 0.6 × inner ramus; inner and outer rami each with 3 robust setae. Uropod 3 peduncle subequal in length with inner ramus; outer ramus 0.6 × inner ramus length; inner ramus with 4 robust setae; outer ramus with 3 robust setae. Telson 1.6 × longer than wide, apex tridentate.

Etymology.

Named for Dr. James Darwin Thomas in recognition of his contribution to amphipod taxonomy, particularly regarding the Leucothoidae . Dr. T has been a mentor and friend for the past 10 years and the first author is very grateful for all his support.

Relationships.

Paranamixis thomasi is similar to Paranamixis aberro in having a cuspate anteroventral head margin and an enlarged gnathopod 2 coxa. Paranamixis thomasi differs in having a serrate ridge on the gnathopod basis instead of a large tubercle and in having plumose setae on the dactylus. Paranamixis thomasi is similar to Paranamixis misakiensis in having the head with a lateral ridge, maxilliped outer plate with a small cleft, an enlarged gnathopod 2 coxa, and a serrate ridge on the gnathopod 2 basis anterior margin. Paranamixis thomasi differs from this species in having a single cusp on the anteroventral head margin, a smaller serrate ridge on the gnathopod 2 basis, and smooth gnathopod 2 carpus and dactylus inner margins.

Ecology.

In the branchial chamber of the solitary ascidian, Pyura sp. (Fig. 18E); and coral rubble.

Remarks.

Both anamorphs and leucomorphs are translucent with magenta-pink stripes along the pereonite edges (Figs 17G, H). When collected in an ascidian, one anamorph and two leucomorphs were collected together from one branchial chamber.

Distribution.

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