Cirolana phuketensis, a new species of marine isopod (Crustacea, Isopoda, Cirolanidae) from the Andaman Sea coast of Thailand

Abstract Cirolana phuketensis sp. n. was collected from coral rubble from the Andaman sea coast of Thailand. C. phuketensis sp. n. is described and fully illustrated; C. phuketensis sp. n. can be recognized by the presence of transverse sutures on pereonites 2–4, pereonite 7 having three transverse sutures forming a nodulose ridge, antennula peduncle with articles 1 and 2 fully fused; pleotelson dorsal surface with 2 sub-median longitudinal carinae, each of which has one prominent tubercle, lateral margins weakly convex, and posterior margin narrow and rounded; 6 molariform robust setae pereopod 1 on inferior margin of merus and the penial openings are two low tubercles. A dichotomous key to species of Cirolana in Thailand is given.


Introduction
Thailand lies in the tropical zone between Pacific Ocean and Indian Ocean. This region has high marine biodiversity (Briggs 2000(Briggs , 2005Briggs and Bowen 2013;Carpenter et al. 2011) but knowledge of marine crustaceans still remains minimal in the region,
Antennula ( Figure 2F) peduncle articles 1 and 2 entirely fused; articles 3 and 4 0.8 times as long as combined lengths of articles 1 and 2; article 3 1.6 times as long as wide, flagellum with 9 articles, antennula extending to anterior margin of pereonite 1. Antenna ( Figure 2G) peduncle article 4 2.2 times as long as wide, 2.4 times as long as article 3, inferior margin with 1 plumose setae, inferodistal margin1 short simple setae; article 5 1.0 times as long as article 4, 2.4 times as long as wide, inferodistal angle with cluster of 3 pappose setae, anterodistal angle with cluster of 4 short simple setae and 2 plumose setae; flagellum with 16 articles, extending to middle of pereonite 4.
Pereopod 1 ( Figure 4A, B) basis 2.0 times as long as greatest width, inferodistal angle with cluster of 2 acute setae; ischium 0.6 times as long as basis, inferior margin with 2 setae, superior distal margin with 2 RS; merus inferior margin with 6 molariform RS (set in row of 5 and 2), superior distal angle with 3 setae; carpus inferior margin with 1 RS (plus 1 slender seta); propodus 1.8 times as long as wide, inferior margin with 2 RS; dactylus ( Figure 4C) 0.7 times as long as propodus; inferior margin lacking setal fringe. Pereopod 2 ( Figure 4D) ischium inferior margin with 2 stout, bluntly rounded RS, superior distal margin with 2 RS; merus inferior margin with 4 stout RS (set in row 3 and 1), superior distal margin with 3 acute RS; carpus inferodistal angle with 2 RS (plus 1 slender seta); propodus 2.3 times as long as wide, with 3 cluster of acute RS; dactylus 1.3 times as long as propodus. Pereopod 3 similar to pereopod 2. Pereopod 4 ( Figure 4E) intermediate in form between pereopod 3 and pereopod 5. Pereopod 6 similar to pereopod 7. Pereopod 7 ( Figure 4F) basis 2.0 times as long as greatest width, superior margin convex, inferior margin with 3 palmate setae; ischium 0.6 times as long as basis, inferior margin with 7 RS (set in group 3 and 4), superior distal angle with 5 RS, inferior distal angle with 4 RS; merus 0.8 time as long as ischium, 1.5 times as long as wide, inferior margin with 3 RS, superior distal angle with 9 RS, inferior distal angle with 7 RS; carpus 0.8 time as long as ischium, 1.5 times as long as wide, inferior margin with 2 RS,  superior distal angle with 17 RS, inferior distal angle with 10 RS; propodus 0.8 times as long as ischium, 2.3 times as long as wide, inferior margin with 3 clusters of RS (set in group 1 and 2), superior distal angle with 2 slender setae (plus 1 plumose seta and 3RS), inferior distal angle with 2 robust setae; dactylus 0.6 times as long as propodus.
Uropod peduncle ( Figure 6A) ventrolateral margin with 2 RS ( Figure 6B), lateral margin with medial short acute RS, posterior lobe about one-half as long as endopod; rami extending beyond pleotelson, marginal setae in single tier. Endopod apically not bifid, broadly round, lateral margin straight, without prominent excision, with 2 RS, mesial margin strongly convex, with 7 RS. Exopod extending beyond end of endopod, 2.4 times as long as greatest width, apically not bifid, notched, lateral margin straight, with 5 RS, mesial margin weakly convex, with 4 RS.
Remarks. Cirolana phuketensis sp. n. is characterized by pereonites 2-4 each with a single transverse suture; pereonites 5-6 each with 2 transverse sutures; pereonites 7 with 3 transverse sutures that also form a nodulose ridge; antennula peduncular articles 1 and 2 fused; pleotelson dorsal surface with 2 sub-median longitudinal carinae, each of which has one prominent anterior tubercle, lateral margin weakly convex and posterior margin narrow rounded; pereopod 1 merus inferior margin with 6 molariform RS; penes in the form of two low tubercles.
Cirolana phuketensis sp. n. belongs to a group of species within Cirolana that is characterised by dorsal is characterised by dorsal nodular ornamentation on the pereon, pleon and pleotelson (Bruce 1986). This group of species has few widely separated robust setae on the uropodal exopod lateral margin, and the pleotelson posterior mar- gin is truncate to narrowly rounded and has 6 or 8 robust seta; there is often clear sexual dimorphism in this group of species, with females more weakly ornamented that males, and dimorphic uropod shape.
Etymology. The epithet is taken from the type locality.