Anamixis sentan, 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 : 13-17

Anamixis sentan sp. n. Figures 1 2

Type material.

Holotype, anamorph male, 2.2 mm RUMF-ZC-1837, Sunabe Seawall, Okinawa–jima Island, Okinawa, spur and groove reef (26°19'25"N, 127°44'43"E), among coral rubble, 3-12 m, K.N. White and N.S. White, col., 17 February 2011 (KNWOkinawa31E). Paratype leucomorph female, 2.1 mm, RUMF-ZC-1838, Sunabe Seawall, Okinawa–jima Island, Okinawa, spur and groove reef (26°19'25"N, 127°44'43"E), among coral rubble, 6-8 m, K.N. White and N.S. White, col., 5 October 2010 (KNWOkinawa12D). Paratype leucomorph male, 1.2 mm, RUMF-ZC-1839, same station data as holotype.

Type locality.

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

Additional material examined.

1 anamorph male, RUMF-ZC-1840, KNWOkinawa24A; 1 anamorph male, NSMT-Cr 21985, KNWTokuno4F; 2 leucomorphs, RUMF-ZC-1841, KNWOkinawa24A; 1 leucomorph, RUMF-ZC-1842, KNWTokuno4F; 1 leucomorph, NSMT-Cr 21986, KNWTokuno4F; 1 leucomorph, RUMF-ZC-1843, KNWOkinawa13C; 4 leucomorphs, NSMT-Cr 21987, KNWOkinawa16H; 1 leucomorph, RUMF-ZC-1844, KNWOkino1B; 1 leucomorph, NSMT-Cr 21988, KNWOkino1B; 3 leucomorphs, RUMF-ZC-1845, KNWOkino2C; 2 leucomorphs, NSMT-Cr 21989, KNWOkino1A; 2 leucomorphs, NSMT-Cr 21990, KNWYoron1B.

Diagnosis.

Anamorph male head anterior margin truncate, anterodistal margin quadrate with cusp; ventral cephalic keel anteroventral margin quadrate with anteriorly projecting cusp. Maxilliped inner plates serrate with small cleft. Gnathopod 2 coxa distal margin with mid-distal projection and posterodistal cusp; propodus palm with 1 large and 1 small triangular projection; dactylus proximal margin setose with indentation. Leucomorph male or female head anterior margin truncate with anterodistal indentation; ventral cephalic keel anterior margin produced and distally excavate.

Description (Anamorph male).

Head. Anterior margin truncate, anterodistal margin quadrate with cusp; ventral cephalic keel anterior margin transverse, anteroventral margin quadrate with anteriorly projecting cusp, ventral margin excavate; eyes present with more than 10 ommatidia, round. Antenna 1 0.4 × body length, flagellum 9-articulate, peduncle article 1 width less than 2 × article 2, accessory flagellum 1-articulate. Antenna 2 0.3 × body length, shorter than antenna 1, flagellum 4-articulate. Mouthparts reduced. Maxilliped inner plates bare; outer plate inner margin smooth, reaching 0.1 × palp article 1, bare; palp 4-articulate, article 4 elongate, distally acute.

Pereon. Pereonite 1 with lateral locking ridge. Coxae 1-4 relative widths 1.0: 1.4: 1.5: 1.3. Gnathopod 1 coxa reduced, anterodistal margin produced, subtriangular, bi-cuspidate, distal margin excavate, posterior margin oblique, facial setae absent; basis linear, anterior and posterior margins bare; ischium bare; carpal lobe curved distally, distal length 7.7 × width, proximal margin smooth, distal margin bare, terminal ornamentation absent; propodus curved, palm serrate with several short proximal setae; dactylus absent. Gnathopod 2 coxa longer than broad, subequal in size with coxa 3, smooth, with tiny marginal setae, anterior margin expanded, anterodistally rounded, distal margin rounded, with mid-distal projection and posterodistal cusp, posterior margin straight, facial setae absent; basis distally expanded, anterior margin with 1 small distal tubercle and 2 short setae, posterior margin bare, ischium bare; carpus 0.9 × propodus length, straight, distally tapered, anterior margin smooth; propodus with 1 mediofacial setal row above midline, reaching 0.3 × propodus length, without submarginal setae, posterior margin smooth, palm linear, with 1 large and 1 small triangular projection distally; dactylus straight, reaching 0.3 × propodus length, proximal margin setose with indentation, anterior margin distally obtuse. Pereopod 3 coxa length 1.3 × width, anterodistal corner overriding distal face of coxa 2, not extending below it, smooth, bare, anterior margin expanded, distal margin oblique with posterodistal cusp, posterior margin rounded, facial setae absent. Pereopod 4 coxa smooth, bare, anterior margin produced, distal margin oblique with mid-distal cusp, posterior margin tapered, facial setae absent. Pereopods 5-7 coxae, facial setae absent; bases width length ratios 1: 1.4, 1: 1.4, 1: 1.3, posterior margins smooth, bare.

Pleon. Epimera 1-3 bare; epimeron 3 posteroventral corner quadrate, produced. Uropods 1-3 relative lengths 1.0: 0.8: 1.1. Uropod 1 peduncle 0.9 × inner ramus length, outer ramus length 0.4 × inner ramus length; inner ramus with 3 robust setae, outer ramus with 1 robust seta. Uropod 2 peduncle 0.8 × inner ramus length, outer ramus 0.4 × inner ramus length; inner ramus with 2 robust setae, outer ramus with 1 robust seta. Uropod 3 peduncle 1.1 × inner ramus length, outer ramus 0.8 × inner ramus length; inner ramus with 3 robust setae, outer ramus with 2 robust setae. Telson 1.1 × longer than wide, apex rounded.

Leucomorph (juvenile and sexually dimorphic characters).

Head. Anterior margin truncate, with small anterodistal indentation, anterodistal margin subquadrate, distal margin straight. Ventral cephalic keel anterior margin produced and distally excavate, anteroventral margin rounded, ventral margin projected downward. Antenna 1 0.3 × body length, flagellum 8-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. Mandibles, upper lip, and lower lip lost in dissection. Maxilla 1 palp 2-articulate with 3 distal setae; outer plate with 5 distal robust setae. Maxilla 2 inner plate with 4 slender setae and 1 robust distal seta; outer plate with 1 distal seta and 8 marginal setae. Maxilliped inner plates fused, distal margin with v-shaped indentation, with large and small robust setae; outer plate inner margin smooth, reaching 0.3 × palp article 1, with simple marginal setae.

Pereon. Coxae 1-4 relative widths 1.0: 2.1: 1.5: 2.2. Gnathopod 1 coxa smooth, with tiny marginal setae, anterior margin oblique, distal margin rounded with cusp, posterior margin oblique, facial setae absent; basis distally expanded, anterior and posterior margins bare; ischium bare; carpus linear, with unclear articulation at distal end, distal length 11.8 × width, proximal margin smooth, distal margin with 1 distal seta, with 2 terminal serrate blades, apically rounded; propodus straight, palm smooth with 8 sets of 2 slender and 1 robust proximal setae; dactylus smooth, reaching less than 0.1 × propodus length. Gnathopod 2 coxa longer than broad, larger than coxa 3, smooth, with tiny marginal setae, anterior margin produced, anterodistally rounded, distal margin rounded, with anterodistal cusp, posterior margin straight, facial setae absent; basis distally expanded, anterior margin with 2 setae, posterior margin with 1 distal seta; ischium bare; carpus 0.3 × propodus length, straight, distally rounded, anterior margin smooth; propodus with 1 mediofacial setal row above midline, reaching 0.3 × propodus length, with 1 row of submarginal setae, posterior margin smooth, palm subtriangular with 7 small and large pointed projections; dactylus curved, reaching 0.4 × propodus length, proximal margin smooth, setose, anterior margin distally acute. Pereopod 3 coxa length 1.5 × width, anterodistal corner overriding distal face of coxa 2 and extending below it, smooth, with tiny marginal setae, all margins straight, corners rounded, facial setae absent. Pereopod 4 coxa smooth, setose, anterior margin straight, distal margin rounded, posterior margin excavate. Pereopods 5-7 coxae facial setae absent; bases length width ratios 1: 1.2, 1: 1.1, 1: 1.2.

Pleon. Epimera 1-2 with ventral setae, epimeron 3 bare, posteroventral corner subquadrate. Uropods 1-3 relative lengths 1.0: 0.7: 1.4. Uropod 1 peduncle 0.7 × inner ramus length, outer ramus 0.4 × inner ramus length; inner ramus with 3 robust setae, outer ramus with 1 robust seta. Uropod 2 peduncle 0.7 × inner ramus length, outer ramus 0.6 × inner ramus length; inner ramus with 1 robust seta, outer ramus with 2 robust setae. Uropod 3 peduncle 1.1 × inner ramus length, outer ramus 0.9 × inner ramus length; inner ramus with 2 robust setae, outer ramus with 3 robust setae. Telson 1.9 × longer than width, apex with weak indentation.

Etymology.

After the Japanese word ‘sentan’, meaning 'pointy end’ and referring to the angular head and ventral cephalic keel (pronounced sen-tahn).

Ecology.

Host unknown, presumably living in sponges in coral rubble.

Relationships.

Anamixis sentan sp. n. fits into the Anamixis bazimut Thomas, 1997, Anamixis kateluensis Thomas, 1997, and Anamixis moana Thomas, 1997group introduced by Thomas (1997). These species share several characters, including a truncate anterior head margin with the ventral cephalic keel extending below the distal head margin and similar shape and morphology of gnathopod 2. Anamixis sentan sp. n. shares the cleft maxilliped inner plates with Anamixis bazimut and Anamixis kateluensis . Anamixis sentan sp. n. is distinct from all other Anamixis species in having serrate maxilliped inner plates in the anamorph; gnathopod 1 coxa anterodistal margin bi-cuspidate, distal margin excavate, and propodus palm smooth with 8 sets of 2 slender and 1 robust proximal setae in the leucomorph.

Remarks.

Anamorph males of Anamixis sentan sp. n. are white in color with 1 robust magenta-pink stripe on each pereonite segment (Figure 15A). Leucomorph males and females are translucent with very faint pink stripes along pereonite edges; some specimens appear to be translucent pink in color (Figure 15B). This species appears to be endemic to the central Ryukyu Islands. The anamorph and leucomorph of this species have not been collected together directly from their host, yet more than one year of collecting has revealed only two anamorph morphologies and two leucomorph morphologies. One anamorph and leucomorph morphology belong to Paranamixis thomasi White and Reimer, 2012a. The other anamorph and leucomorph morphology are described here as Anamixis sentan , although there is a very slight chance that this leucomorphbelongs to a different anamorph counterpart that has not been collected.

Distribution.

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