Cirolana siamensis, 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 : 23-31

Cirolana siamensis sp. nov.

( Figures 12 – 16 )

Material examined

Holotype, ♂ (6.5 mm), Koh Talu , Prachuap Khiri Khan Province, 11°04 ’ 45"N, 99°33 ’ 23"E, 17 July 2011, trapped at a depth of 8 – 10 m, coral rubble, coll. E. Rodcharoen ( PSUZC – CR0284-01 ).

Paratypes, all material from eastern coast, Gulf of Thailand. 5 ♂ (6.4, 6.5, 6.2, 6.8, 6.3 mm [dissected]), 5 ♀ (6.6, 6.9, 6.9, 6.1, 6.0 mm [dissected]), same data as holotype ( PSUZC – CR0284-02; MTQ W34354).

Description of male

Body 3.3 times as long as greatest width, widest at pereonite 5. Body lateral margins subparallel ( Figure 12 A). Eyes black, separated by about 53% of width of head ( Figure 12 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 12 B). Pleon ( Figure 12 E) 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 4; 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 0.8 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 16 E, F).

Antennula ( Figure 12 F) peduncle articles 1 and 2 distinct, articulated; article 2 0.6 times as long as article 1; articles 3 and 4 0.8 times as long as combined lengths of articles 1 and 2; article 3 2.1 times as long as wide, flagellum with 11 articles extending to anterior of pereonite 1. Antenna ( Figure 12 G) peduncle article 4 1.9 times as long as wide, 2.0 times as long as article 3, article 5 1.1 times as long as article 4, 2.5 times as long as wide, inferodistal angle with 1 pappose seta, anterodistal angle with cluster of 2 pappose setae and 5 long simple setae, flagellum with 26 articles, extending to posterior of pereonite 4 to anterior of pereonite 5.

Frontal lamina ( Figure 12 D) pentagonal, 2.2 times as long as posterior width, 1.6 times as long as greatest width, lateral margins straight, diverging slightly towards anterior, anterior margin acute, with small median point.

Mandible molar process ( Figure 13 A, C) anterior margin with 23 flat teeth; with proximal cluster of long simple setae; right mandible spine row composed of 12 spines, left with 12 spines; palp articles 2 with 21 distolateral setae, palp article 3 with 21 robust biserrate setae ( Figure 13 B). Maxillule ( Figure 13 E) mesial lobe with 3 large and circumplumose RS; lateral lobe with 10 RS. Maxilla ( Figure 13 D) lateral lobe with 6 long simple setae, middle lobe with 12 long simple setae, mesial lobe with 14 simple setae and plumose setae. Maxilliped palp ( Figure 13 F) article 2 mesial margin with 7 slender setae, lateral margin distally with 1 slender seta; article 3 mesial margin with 13 slender setae, lateral margin with 5 slender setae, article 4 mesial margin with 17 slender setae, lateral margin with 4 slender setae, article 5 distal margin 19 setae, lateral margin with 5 setae; endite ( Figure 13 G) with 3 long CPS and 2 coupling setae.

Pereopod 1 ( Figure 14 A, B) basis 2.3 times as long as greatest width, inferior distal angle with cluster of 2 acute setae; ischium 0.7 times as long as basis, inferior margin with 1 acute seta, 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 3 setae. propodus 2.0 times as long as wide, inferior margin with 2 RS; dactylus ( Figure 14 C) 0.7 times as long as propodus, inferior margin with setal fringe on carpus and propodus. Pereopod 2 ( Figure 14 D) ischium inferior margin with 3 stout, bluntly rounded RS, superior distal margin with 3 RS, merus inferior margin with 7 stout RS (set in rows of 4 and 3, superior distal margin with 4 acute RS; carpus inferodistal angle with 3 RS (plus 1 long slender seta). Propodus 2.3 times as long as wide, with 2 clusters of acute RS. dactylus 0.7 times as long as propodus. Pereopod 3 similar to pereopod 2. Pereopod 4 ( Figure 14 E) intermediate in from between pereopod 3 and pereopod 5. Pereopod 6 similar to pereopod 7. Pereopod 7 ( Figure 14 F) basis 2.2 times as long as greatest width, superior margin weakly convex, inferior margin with 2 palmate setae; ischium 0.6 times as long as basis, inferior margin with 5 RS (set in groups of 2 and 3), superior distal angle with 6 RS (2 biserrate), inferior distal angle with 3 RS; merus 0.8 times as long as ischium, 1.7 times as long as wide, inferior margin with 2 RS, superior distal angle with 14 RS (10 biserrate), inferior distal angle with 7 RS; carpus 0.9 times as long as ischium, 2.5 times as long as wide, inferior margin with 2 RS, superior distal angle with 11 RS (6 biserrate), inferior distal angle with 11 RS (5 biserrate); propodus 1.0 time as long as ischium, 4.1 times as long as wide, inferior margin with 4 clusters of RS (set in groups of 2 and 2), superior distal angle with 2 slender setae (plus 2 RS and 1 plumose), inferior distal angle with 2 RS, dactylus 0.4 times as long as propodus.

Penes ( Figure 12 H) low tubercles, penial openings separated by 13% of sternal width.

Pleopod 1 ( Figure 15 A) exopod 1.7 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 14 PMS on distal margin only; peduncle 1.8 times as wide as long, mesial margin with 5 coupling hooks. Pleopod 2 ( Figure 15 B) exopod with 35 PMS, endopod with 16 PMS; appendix masculina laterally curved, 1.6 times as long as endopod, distally acute. Pleopod 3 ( Figure 15 C) exopod with 37 PMS, endopod with 13 PMS. Pleopod 4 ( Figure 15 D) exopod with 38 PMS, endopod with 9 PMS. Pleopod 5 ( Figure 15 E) exopod with 34 PMS. Pleopods 2 – 5 peduncle distolateral margin with prominent acute RS, endopods 3 – 5 with distomesial serrate scales.

Uropod ( Figure 16 A, B) peduncle ventrolateral margin with 2 RS (plus 3 long setae), 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 ( Figure 16 A) apically deeply and equally bifid ( Figure 16 D), lateral margin weakly convex, without prominent excision, with 3 RS, mesial margin weakly convex, with 4 RS. Exopod ( Figure 16 A) not extending to end of endopod, 0.8 times as long as endopod, 2.8 times as long as greatest width, apically deeply and equally bifid ( Figure 16 C), lateral margin weakly convex, with 6 RS, mesial margin convex, with 3 RS.

Female

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

Size

Adult males (n = 5) 6.2 – 6.8 mm (mean 6.4 mm); females (n = 5) 6.1 – 6.9 mm (mean 6.5 mm).

Variation

Pleotelson (n = 10 [5 ♂ and 5 ♀]) with 7 – 9 RS, with 8 RS (4 + 4) most frequent (80%), 7 (10%) and 9 (10%) occurring only once. Uropod endopod mesial margin with 4 – 5 RS, with 4 (60%) most frequent and 5 (40%), lateral margin with 3 RS (100; exopod mesial margin with 3 RS (100%), lateral margin with 6 – 7 RS, with 6 (50%) and 7 (50%).

Remarks

Cirolana siamensis sp. nov. can be identified by having antennula peduncle articles 1 and 2 distinct and articulated; antenna extending to posterior of pereonite 4 to anterior of pereonite 5; 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; the penes are two low tubercles, with the openings separated by 13% of sternal width; pleopod 1 endopod lateral margin is straight; the appendix masculina is laterally curved, 1.6 times as long as endopod and distally acute; uropod peduncle ventrolateral margin has two robust setae (plus three long setae), rami extending beyond pleotelson; endopod apically deeply and equally bifid, lateral margin with three robust setae, mesial margin with four robust setae; exopod apically deeply and equally bifid, lateral margin with six robust setae, mesial margin with three robust setae; pleotelson with eight robust setae.

Three Indo-Pacific species are similar to Cirolana siamensis sp. nov. – Cirolana paraerodiae Müller and Salvat, 1993 ( French Polynesia), Cirolana erodiae Bruce, 1986 (Great Barrier Reef) and Cirolana portula Bruce, 1986 (Western Australia). Shared characters between C. siamensis sp. nov. and those three species are the presence of setal fringe on pereopod 1 on male, antennula peduncle with four articles and a laterally curved appendix masculina. Cirolana siamensis sp. nov. can be separated from C. paraerodiae by the antenna flagellum extending to pereonite 5 (vs pereonite 3), and C. siamensis sp. nov. has a distinctly longer appendix masculina than C. paraerodiae does (1.6 vs 1.3 times as long as endopod). Cirolana siamensis sp. nov. differs from C. erodiae in having pereopod 1 with a setal fringe on carpus and propodus, while C. erodiae is without or with setal fringe on merus, carpus and propodus. Moreover, the antenna of C. siamensis sp. nov. is slightly longer than that of C. erodiae (antenna extending beyond pereonite 5 vs pereonite 4). Cirolana siamensis sp. nov. differs from C. portula by having a shorter appendix masculina than C. portula (1.6 vs 1.8 times as long as endopod) and C. siamensis sp. nov. with uropod rami lateral margin weakly convex (vs uropod rami lateral margin sinuate).

In comparison to the other species occurring in Thailand Cirolana siamensis sp. nov., is most similar to the sympatric Cirolana thailandica sp. nov., both species with antennula peduncle four articles, having a setal fringe on the male pereopod 1, and pleopod 1 of endopod with a straight lateral margin. However, the two species differ in the characters of appendix masculina and rami apex of uropod. Cirolana siamensis sp. nov. has the appendix masculina 1.6 times as long as the endopod, laterally curved; uropodal rami with the apices deeply and equally bifid, whereas C. thailandica sp. nov. has the appendix masculina 1.9 times as long as the endopod, laterally straight; uropodal rami with apices deeply divided and lateral process prominent.

Etymology

The epithet is derived from Siam, the previous name of Thailand, alluding to the type locality in the Gulf of Siam.

Figures

Figure 12. Cirolana siamensis sp. nov., male holotype PSUZC – CR 0284 - 01 (6.5 mm). (A – E, H), male paratype PSUZC – CR 0284 - 02 (6.4 mm) (F, G). (A) dorsal view; (B) lateral view; (C) head; (D) frons; (E) pleon; (F) antennula; (G) antenna peduncle; (H) penial opening, sternite 7.

Figure 13. Cirolana siamensis sp. nov., male paratype PSUZC – CR 0284 - 02 (6.4 mm). (A) right mandible; (B) dorsal view of article 3 of right mandible palp; (C) distal part of left mandible; (D) right maxilla; (E) right maxillule; (F) right maxilliped; (G) endite.

Figure 14. Cirolana siamensis sp. nov., male paratype PSUZC – CR 0284 - 02 (6.4 mm). (A) pereopod 1; (B) mesial view of pereopod 1; (C) mesial view of dactylus of pereopod 1; (D) pereopod 2; (E) pereopod 4; (F) pereopod 7.

Figure 15. Cirolana siamensis sp. nov., male paratype PSUZC – CR 0284 - 02 (6.4 mm). (A – E) pleopods 1 – 5, respectively.

Figure 16. Cirolana siamensis sp. nov., male paratype PSUZC – CR 0284 - 02 (6.4 mm). (A) uropod; (B) ventral view of uropod peduncle and exopod; (C) uropod exopod apex; (D) uropod endopod apex; (E) pleotelson; (F) pleotelson apex.