Cirolana thailandica, Eknarin Rodcharoen, Niel L. Bruce & Pornsilp Pholpunthin, 2016

Eknarin Rodcharoen, Niel L. Bruce & Pornsilp Pholpunthin, 2016, Description of four new species of the Cirolana ‘ parva group’ (Crustacea: Isopoda: Cirolanidae) from Thailand, with supporting molecular (COI) data, Journal of Natural History 50 (31 - 32), pp. 1935-1981 : 31-40

Cirolana thailandica sp. nov.

( Figures 17 – 22 )

Material examined

Holotype, ♂ (6.9 mm), Ao Karang, Koh Samet , Yayong Province, 12°31 ’ 33"N, 101°26 ’ 46"E, 1 August 2012, trapped at a depth of 1 m, coral rubble, coll. E. Rodcharoen ( PSUZC – CR0285-01 ).

Paratypes, all material from eastern coast, Gulf of Thailand, 9 ♂ (7.7, 7.8, 7.7, 6.9, 7.4, 7.6, 7.6, 7.6, 8.0 mm [dissected], 67 specimens unmeasured, same data as holotype ( PSUZC – CR0285-02). 7 ♂ (7.2, 6.8, 7.6, 5.9, 6.3, 5.8, 6.2 mm [dissected]), 1 ♀ (6.2 mm [dissected]), 17 specimens unmeasured, Pratiw, Chumphon Province, 10° 43 ’ 11"N, 99°51 ’ 23"E, 14 July 2011, trapped at a depth of 2 – 3 m, dead coral and seaweed bed, coll. E. Rodcharoen ( PSUZC – CR0285-03; MTQ W34352). 5 ♂ (unmeasured), Koh Chang, Trat Province (12°08 ’ 29"N, 102°17 ’ 0 1"E), 4 August 2012, trapped at a depth of 1 m, coral rubble, coll. E. Rodcharoen ( PSUZC – CR0285-04). 13 ♂ (unmeasured), Samae San, Chonburi Province, 12°36 ’ 21"N, 100°57 ’ 32"E, 30 July 2012, trapped at a depth of 7 m, coral reef, coll. E. Rodcharoen ( PSUZC – CR0285-05).

Description of male

Body 3.1 times as long as greatest width, widest at pereonite 5, lateral margins subparallel ( Figure 17 A). Eyes dark brown, separated by about 63% width of head ( Figure 17 C). Pereonite 1 and coxae 2 – 3 each with posteroventral angle rounded; coxae 5 – 7 with entire oblique carina; posterior margins of pereonites 5 – 7 smooth ( Figure 17 B). Pleon ( Figure 17 D) with pleonite 1 largely concealed by pereonite 7; pleonites 3 – 5 posterior margins smooth; posterolateral angles of pleonite 2 forming acute point, extending posteriorly to anterior of pleonite 5; pleonite 3 with posterolateral margins extending clearly beyond posterior margins of pleonites 4 and 5, acute; posterolateral margin of pleonite 4 rounded, clearly extending beyond posterior margin of pleonite 5; pleonite 5 with posterolateral angles overlapped by lateral margins of pleonite 4. Pleotelson 0.9 times as long as anterior width, dorsal surface without longitudinal carina; lateral margins weakly convex; margins smooth, posterior margin converging to caudomedial point, with small distinct median point, with 8 RS ( Figure 22 E, F).

Antennula ( Figure 17 F) peduncle articles 1 and 2 distinct, articulated; article 2 0.8 times as long as article 1; article 3 and 4 0.9 times as long as combined lengths of articles 1 and 2, article 3 2.4 times as long as wide; flagellum with 9 articles extending to anterior of pereonite 1. Antenna ( Figure 17 G) peduncle article 4 2.0 times as long as wide, 2.1 times as long as article 3, inferior margin with 1 plumose seta; article 5 1.0 time as long as article 4, 2.3 times as long as wide, inferodistal angle with cluster of 2 pappose setae and 1 long simple seta, anterodistal angle with cluster of 2 pappose setae and 4 simple setae; flagellum with 24 articles, extending to middle of pereonite 4.

Frontal lamina ( Figure 17 E) pentagonal; 1.9 times as long as posterior width; 1.7 times as long as greatest width, lateral margins straight, diverging slightly towards anterior, anterior margin acute, with small median point.

Mandible molar process ( Figure 18 A, C, D) anterior margin with 25 flat teeth; with proximal cluster of long simple setae; left spine row with 11 spines; palp article 2 with 11 distolateral setae; palp article 3 lateral margin with 14 robust biserrate setae ( Figure 18 B), distal margin with 3 biserrate setae and 1 long simple seta. Maxillule ( Figure 18 E) mesial lobe with 3 large and circumplumose RS; lateral lobe with 13 RS (weakly serrated). Maxilla ( Figure 18 F) lateral lobe with 5 long simple setae, middle lobe with 9 long simple setae, mesial lobe with 5 distal simple setae and 9 proximal simple and plumose setae. Maxilliped palp ( Figure 18 G) article 2 mesial margin with 6 slender setae, lateral margin distally with 1 slender seta; article 3 mesial margin with 14 slender setae, lateral margin with 6 slender setae; article 4 mesial margin with 15 slender setae, lateral margin with 4 slender setae, article 5 distal margin with 17 setae, lateral margin with 4 setae; endite ( Figure 18 H) with 5 long CPS and 2 coupling setae.

Pereopod 1 ( Figure 19 A, C) basis 2.4 times as long as greatest width, inferior distal angle with cluster of 4 acute setae; ischium 0.5 times as long as basis, inferior margin with 1 acute seta and 1 RS, inferior distal angle with 3 RS, superior distal margin with 2 RS; merus inferior margin with 5 molariform RS (set in rows of 3 and 2), superior distal angle with 4 setae; carpus inferior distal margin with 1 long simple seta; propodus 1.7 times as long as wide, inferior margin with 2 slender setae; dactylus ( Figure 19 B) 0.8 times as long as propodus, inferior margin with setal fringe on propodus and carpus. Pereopod 2 ( Figure 19 D) ischium inferior margin with 2 stout, bluntly rounded RS, superior distal margin with 3 RS; merus inferior margin with seven stout RS (set in rows of 4 and 3), superior distal margin with 6 acute RS; carpus inferodistal angle with 3 RS (2 simple and 1 biserrate) and 1 simple long seta; Propodus 2.5 times as long as wide; dactylus 0.7 times as long as propodus. Pereopod 3 similar to pereopod 2. Pereopod 4 ( Figure 19 E) intermediate in form between pereopod 3 and pereopod 5. Pereopod 6 ( Figure 20 A, B) similar to pereopod 7. Pereopod 7 ( Figure 20 C, D) longer than pereopod 6, basis 2.2 times as long as greatest width, superior margin convex, inferior margin with 2 palmate setae; ischium 0.7 times as long as basis, inferior margin with 6 RS (set in groups of 2, 3 and 1), superior distal angle with 6 RS (3 biserrate), inferior distal angle with 4 RS; merus 0.7 times as long as ischium, 1.6 times as long as wide, inferior margin with 2 RS, superior distal angle with 11 RS (6 biserrate), inferior distal angle with 7 RS (only simple); carpus 0.7 times as long as ischium, 2.2 times as long as wide, inferior margin with 2 RS, superior distal angle with 9 RS (5 simples and 4 biserrate), inferior distal angle with 12 RS (6 biserrate); propodus 1.0 time as long as ischium, 4.2 times as long as wide, inferior margin with 5 RS (set in groups of 2 and 3), superior distal angle with 5 setae (2 RS, 2 simple and 1 plumose), inferior distal angle with 2 RS. Dactylus 0.3 times as long as propodus.

Penes ( Figure 17 H) 2 low tubercles, penial openings separated by 12% of sternal width.

Pleopod 1 ( Figure 21 A) exopod 1.6 times as long as wide, lateral margin weakly convex, distally broadly rounded, mesial margin strongly convex, with 25 PMS from distal one-third; endopod 2.2 times as long as wide, distally broadly rounded, lateral margin straight, with 12 PMS on distal margin; peduncle 1.6 times as wide as long, mesial margin with 5 coupling hooks. Pleopod 2 ( Figure 21 B) exopod with 28 PMS, endopod with 16 PMS; appendix masculina with parallel margins, 1.9 times as long as endopod, distally acute. Pleopod 3 ( Figure 21 C) exopod with 32 PMS, endopod with 10 PMS. Pleopod 4 ( Figure 21 D) exopod with 33 PMS, endopod with 9 PMS. Pleopod 5 exopod ( Figure 21 E) with 31 PMS. Pleopods 2 – 5 peduncle distolateral margin with prominent acute RS, endopods 3 – 5 with distomesial serrate scales.

Uropod ( Figure 22 A, D) peduncle ventrolateral margin with 2 RS (plus 3 long setae), lateral margin with mesial short acute RS, posterior lobe about one-half as long as endopod; rami extending beyond pleotelson, marginal setae in single tier. Endopod ( Figure 22 A, C) apically deeply bifid, lateral process prominent; lateral margin straight, without prominent excision, with 2 RS, mesial margin weakly convex, with 4 RS. Exopod ( Figure 22 A) not extending to end of endopod, 0.9 times as long as endopod, 2.5 times as long as greatest width, apically deeply bifid, lateral process prominent ( Figure 22 B); lateral margin weakly convex, with 7 RS; mesial margin weakly convex, with 3 RS.

Sub-adult male

Pereopod 1 has a less well-developed setal fringe than in adult males.

Female

Of similar appearance to male but lacks a setal fringe on pereopod 1.

Variation

Pleotelson (n = 18 [17 ♂ and 1 ♀]) with 7 – 9 RS, with 8 RS (4 + 4) most frequent (82%), 7 (12%), and 9 (6%) occurring only once. Uropod endopod mesial margin with 3 – 5 RS, with 4 (76%) most frequent, 3 (12%) and 5 (12%), lateral margin with 2 – 4 RS, with 3 (88%) most frequent, 2 (6%) and 4 (6%) occurring only once; exopod mesial margin with 2 – 3 RS, with 3 (94%) most frequent and 2 (6%) occurring only once, lateral margin with 7 – 8 RS, with 7 (65%) most frequent and 8 (35%).

Size

Adult males (n = 17) 5.8 – 8.0 mm (mean 7.1 mm); females (n = 1) 6.2 mm.

Remarks

Cirolana thailandica sp. nov. is characterised by antennula peduncle articles 1 and 2 distinct, articulated; antenna flagellum extending to middle of pereonite 4; pereopod 1 on male with setal fringe on carpus and propodus; pleonite 3 with posterolateral margins extending clearly beyond posterior margins of pleonites 4 and 5; penes two low tubercles, penial openings separated by 12% of sternal width; pleopod 1 endopod lateral margin straight, appendix masculina distally acute, with parallel margins, 1.9 times as long as endopod; uropod peduncle ventrolateral margin with two robust setae (plus three long setae), rami extending beyond pleotelson; endopod apically deeply bifid, lateral process prominent, lateral margin with two robust setae, mesial margin with four robust setae; exopod apically deeply bifid, lateral process prominent, lateral margin with seven robust setae, mesial margin with three robust setae; pleotelson with eight robust setae.

Cirolana thailandica sp. nov. is similar to Cirolana arafurae Bruce, 1986 from the Kei Islands, Indonesia, in having the antennula peduncle with four articles and a similar numer of robust setae on lateral margin of uropod rami. However, C. arafurae differs from C. thailandica sp. nov. in having pereopod 1 of male with a setal fringe on merus, carpus and propodus, whereas all male of C. thailandica sp. nov. have the setal fringe on carpus and propodus only. Moreover, the appendix masculina of C. arafurae is 1.6 times as long as endopod (vs 1.9) and lateral margin of uropodal exopod with six robust setae (vs seven robust setae).

The other similar species of Cirolana with a setose fringe on the male pereopod 1 carpus and propodus is the cool-water New Zealand species Cirolana kokoru Bruce, 2004 . However, Cirolana thailandica sp. nov. can be clearly distinguished from C. kokoru by the body size; C. kokoru is larger than C. thailandica sp. nov. (male average at 9.5 vs 7.1 mm, female at 8.6 vs 6.2 mm). Additional distinguishing characters include the appendix masculina, which in C. thailandica sp. nov. has 1.9 times as long as endopod, narrowing gradually to an acute point (vs 1.3 times as long as endopod, distally notched in C. kokoru ). Moreover, C. thailandica sp. nov. generally has less numerous robust setae on the uropodal rami and pleotelson than C. kokoru does; uropod exopod lateral margin with seven robust setae (vs nine robust setae); endopod mesial margin with four robust setae (vs eight robust setae) and pleotelson with eight robust setae (vs ten robust setae).

Etymology

Cirolana thailandica sp. nov. is named for the type locality.

Molecular analysis

The target gene region of mitochondrial protein-coding gene cytochrome – c – oxidase (CO1, ~700 bp) of Cirolana ‘ parva group ’ species occurring in Thailand was analysed to investigate the relationship between those species. The tree is shown in Figure 23 A, B). Both ML and bayesian analysis reveal the same tree topology that is strongly supportive of a monophyletic clade within Cirolana ‘ parva group ’ species (ML = 100% and BI = 1). The tree of ML analysis ( Figure 23 A) clearly showed two principal clades within Cirolana ‘ parva group ’ species. Clade 1 includes only specimens of C. andamanensis sp. nov., and clade 2 includes three species ( C. thailandica sp. nov., C. phangnga sp. nov. and C. siamensis sp. nov.). Bayesian analysis ( Figure 23 B) also shows C. andamanensis sp. nov. is sister to the clade of the three other species, while the relationship of C. thailandica sp. nov. to the other two species within the second clade is unresolved.

The uncorrected p-distances (COI) between the species members of the Cirolana ‘ parva group ’ from Thailand are shown in Table 3 . The genetic distance within the same species ranges from 0 to 1.6%, whereas the differences between species ranged from 22.5 to 32.1%. The highest value of 32.1 is between C. thailandica and C. andamanensis , while the lowest value of 22.5 is between C. phangnga and C. siamensis .

Figures

Figure 17. Cirolana thailandica sp. nov., male holotype PSUZC – CR 0285 - 01 (6.9 mm). (A, C), male paratype PSUZC – CR 0285 - 03 (7.1 mm) (B, D – E, H), male paratype PSUZC – CR 0285 - 02 (7.4 mm) (F, G). (A) dorsal view; (B) lateral view; (C) head; (D) pleon; (E) frons; (F) antennula; (G) antenna peduncle; (H) penial opening, sternite 7.

Figure 18. Cirolana thailandica sp. nov., male paratype PSUZC – CR 0285 - 02 (7.4 mm). (A) left mandible; (B) robust seta; (C) distal part of left mandible; (D) distal part of right mandible; (E) right maxillule; (F) right maxilla; (G) right maixlliped; (H) endite.

Figure 19. Cirolana thailandica sp. nov., male paratype PSUZC – CR 0285 - 02 (7.4 mm). (A) pereopod 1; (B) dactylus of pereopod 1; (C) mesial view of pereopod 1; (D) pereopod 2; (E) pereopod 4.

Figure 20. Cirolana thailandica sp. nov., male paratype PSUZC – CR 0285 - 02 (7.4 mm). (A) lateral of pereopod 6; (B) mesial of pereopod 6; (C) lateral of pereopod 7; (D) mesial of pereopod 7.

Figure 21. Cirolana thailandica sp. nov., male paratype PSUZC – CR 0285 - 02 (7.4 mm). (A – E) pleopods 1 – 5, respectively.

Figure 22. Cirolana thailandica sp. nov., male paratype PSUZC – CR 0285 - 02 (7.4 mm). (A) uropod; (B) uropod exopod apex; (C) uropod endopod apex; (D) ventral view of uropod peduncle and exopod; (E) pleotelson; (F) pleotelson apex.

Figure 23. Phylogenetic relationships of the Cirolana ‘ parva group ’ taxa described in this study. (A) phylogenetic tree of ML analysis; (B) phylogenetic tree of Bayesian analysis. Number above each node shows ML bootstrap percentages and Bayesian posterior probability, respectively. Cirolana sp. 1 and sp. 2 are representatives of the Cirolana ‘ tuberculate group ’ which were used as the outgroup.