Cirolana khamensis, Rodcharoen & Bruce, 2021

Rodcharoen, Eknarin & Bruce, Niel L., 2021, Two new species of the marine isopod genus Cirolana Leach, 1818 (Crustacea Isopoda: Cirolanidae) from the coast of the western Gulf of Thailand, Zootaxa 4950 (3), pp. 469-486 : 471-478

Cirolana khamensis sp. nov.

( Figs 2–7 )

Material examined. Holotype: ♂ (6.5 mm), Koh Kham , Songkhla Province, 6°58’18.84” N, 100°51’25.54”E, 9 July 2011, trapped at 8 m depth, coral reef, coll. E. Rodcharoen ( PSUZC-CR2087-01 ).

Paratypes: 9 ♂ (7.9, 8.2, 7.3, 7.7, 8.3, 7.1, 7.6, 8.2, 8.4 mm) [dissected]), 7 ♀ (7.4, 7.8, 8.5, 7.9, 8.3, 8.5, 7.8 mm [dissected]), same data as holotype, ( PSUZC-CR2087-02 ) .

Description of male. Body dorsal surfaces punctuate, widest at pereonite 5 or pereonite 6, lateral margins subparallel. Rostral point absent. Eyes colour brown in alcohol; eyes separated by about 80% width of head. Pereonites 1–3 each with a single transverse impressed line, pereonites 4–6 each with 2 transverse impressed lines; pereonite 7 with 3 tranverse lines with posterior line forming nodulose ridge. Pereonite 1 and coxae 2–3 each with posteroventral angle rounded; coxae 5–7 with entire oblique carina. Pleon with pleonite 1 largely concealed by pereonite 7; pleonites 3–5 with tubercles; posterolateral angles of pleonite 2 rounded, extending posteriorly to anterior of pleonite 4; pleonite 3 with row of 11–13 tubercles, posterolateral margins extending to but not beyond posterior margin of pleonite 5, narrow rounded; pleonite 4 with prominent median tubercles and 3–4 sublateral tubercles on each side, posterolater margins rounded, clearly extending beyond posterior margin of pleonite 5; pleonite 5 with prominent median tubercles and 2–3 sublateral tubercles on each side, posterolateral angles overlapped by lateral margins of pleonite 4. Pleotelson 0.7 times as long as anterior width, dorsal surface with paired submedian logitudinal carina, each of which has 4 tubercles; lateral margins weakly concave; margins smooth, posterior margin evenly rounded, with 8 robust setae.

Antennula peduncle articles 1 and 2 distinct articulated; article 2 0.5 times as long as article1; article 3 and 4 0.9 times as long as combined lengths of articles 1 and 2, article 3 1.8 times as long as wide; flagellum with 9 articles, extending to posterior margin of eye. Antenna peduncle article 4 1.8 times as long as wide, 2.6 times as long as article 3, posterodistal angle with 1 short simple seta; article 5 1 times as long as article 4, 2.5 times as long as wide, anterodistal angle with cluster of 4 setae (2 simple and 2 palmate setae), anterodistal angle with cluster of 2 simple setae and 2 palmate setae; flagellum with 20 articles, extending to middle of pereonite 3.

Frontal lamina pentagonal, 2.2 times as longer than greatest width, lateral margins straight, diverging slightly towards anterior, anterior margin acute.

Left mandible molar process anterior margin with 15 flat teeth; with proximal cluster of long simple setae; left mandible spine row composed of 8 spines; palp articles 2 with 14 distolateral setae, palp article 3 with 17 biserrate RS. Left maxillula mesial lobe with 3 large and circumplumose RS; lateral lobe with 12 RS. Right maxilla lateral lobe with 5 long setae; middle lobe with 13 long setae; mesial lobe with 3 distal long setae and 12 proximal long setae. Right maxilliped palp article 2 mesial margin with 7 slender setae, lateral margin distally with 1 slender seta; article 3 mesial margin with 14 slender setae, lateral margin with 9 slender setae; article 4 mesial margin with 13 slender setae, lateral margin with 5 slender setae; article 5 distal margin 17 setae, lateral margin with 4 setae; endite with 5 long CPS, and 1 coupling setae (both left and right).

Pereopod 1 basis 2.3 times as long as greatest width, infererior distal angle with cluster of 2 acute setae; ischium times 0.6 times as long as basis, inferior margin with 2 setae, superior distal margin with 1 RS; merus inferior margin with 6 molariform RS (set as in row of 4+2), superior distal angle with 4 setae (slender); carpus inferior distal margin with 2 setae (1 RS and 1 slender seta). Propodus 2.0 times as long as wide, inferior margin with 3 RS; dactylus 0.7 times as long as propodus. Pereopod 2 ischium inferior margin with 2 stout, bluntly rounded RS, superior distal margin with 3 RS (2 simple and 1 biserrate); merus inferior margin with 8 stout RS (set in row of 5 molariform and 3 acute), superior distal margin with 4 acute RS; carpus inferodistal angle with 3 RS (plus 1 slender seta); propodus 1.7 times as long as wide; dactylus 0.9 times as long as propodus. Pereopod 3 similar to pereopod 2. Pereopod 4 intermediate in form between pereopod 3 and pereopod 5. Pereopod 6 similar to pereopod 7. Pereopod 7 basis 2.8 times as long as greatest width, superior margin convex, inferior margin with 4 palmate setae; ischium 0.6 times as long as basis. inferior margin with 7 RS (set in groups of 3, 1 and 3), superior distal angle with 6 RS, inferior distal angle with 2 RS; merus 0.7 times as long as ischium, 1.3 times as long as wide, inferior margin with 4 RS (set in groups of 1 and 3), superior distal angle with 13 RS (2 simple and 11 biserrate), inferior distal angle with 6 RS; carpus times 0.9 times as long as ischium, 1.7 times as long as wide, inferior margin with 3 RS, superior distal angle with 13 RS (simple and biserrate), inferior distal angle with 10 RS (6 simple and 4 biserrate); propodus 1.0 time as long as ischium, 4.4 times as long as wide, inferior margin with 4 RS (set in group 2 and 2), superior distal angle with 3 RS, 1 slender seta and 1 palmate seta, inferior distal angle with 2 RS; dactylus 0.4 times as long as propodus.

Penial openings two low tubercles, separated by 25% of sternal width.

Pleopod 1 exopod 1.4 times as long as wide, lateral margin straight, distally broadly rounded, mesial margin strongly convex, with 30 PMS from distal one-third; endopod 2.2 times as long as wide, distally broadly rounded, lateral margin sinuate, with 10 PMS on distal margin only; peduncle 1.6 times as wide as long, mesial margin with 4 coupling hook. Pleopod 2 exopod with 38 PMS, endopod with 13 PMS; appendix masculina with parallel margins, 1.1 times as long as endopod, distally narrowly rounded. Pleopod 3 exopod with 40 PMS, endopod with 11 PMS. Pleopod 4 exopod with 38 PMS, endopod with 9 PMS. Pleopod 5 exopod with 34 PMS. Pleopods 2–5 peduncle distolateral margin with prominent acute RS.

Uropod peduncle ventrolateral margin with 2 RS, lateral margin with 1 mesial short acute RS, posterior lobe about one-half as long as endopod; rami extending beyond pleotelson, marginal setae in single tier, apices broadly round. Endopod apically not bifid; lateral margin distally convex, without prominent excision, with 2 RS, mesial margin strongly convex, with 7 RS. Exopod not extending to end of endopod, 1.5 times as long as greatest width, apically shallowly and equally sub-bifid; lateral margin weakly convex, with 5 RS; mesial margin convex, with 4 RS.

Female. Similar to male but on average a little larger (see ‘Size’).

Variation. Pleotelson (n=17 [10♂ and 7♀]) with 7–8 RS, with 8 RS (4+4) most frequent (76%). Uropod endopod mesial margin with 6–8 RS, with 7 (76%) and 6 (18%) most frequent and 8 (6%) occurring only once, lateral margin with 2 RS (100%); exopod mesial margin with 4 RS (100%), lateral margin with 5 RS (100%).

Size. Adult males (n=10) 6.5–8.3 mm (mean 7.7 mm); females (n=7) 7.4–8.5 mm (mean 8.0 mm).

Remarks. Cirolana khamensis sp. nov. is characterized by pereonites 1–3 each with a single transverse impressed line; pereonites 4–6 with each with two transverse impressed lines; pereonite 7 with three transverse lines with the posterior line forming a nodulose ridge; the antennula peduncular articles 1 and 2 are distinct and articulated; pleotelson dorsal surface with two sub-median longitudinal carinae, each of which has four prominent tubercles, posterior margin evenly rounded, with eight robust setae; pereopod 1 merus inferior margin with six molariform RS; lateral margin of uropodal exopod having continuous row of PMS; and penes in the form of two low tubercles separated by 25% of sternal width.

We place Cirolana khamensis into the Cirolana ‘pleonastica -group’ as the species shows all the characters for that group, with the exception of the uropodal exopod lateral margin, which has setae along the distal two-thirds of its length, though not the entire length. Nonetheless, the morphology and setation of the uropodal exopod is closer to that of the Cirolana ‘pleonastica -group’ than to the other clades, and furthermore C. khamensis lacks the defining characters of the other groups (see Sidabalok 2019). In their diagnosis of the ‘pleonastica -group’, Sidabalok & Bruce (2018a) state the uropod exopod lateral margin character is usually present.

Similar South-East Asian species in the Cirolana ‘pleonastica -group’ are Cirolana phuketensis Rodcharoen et al., 2017 ( Thailand) , C. merlion Sidabalok & Bruce, 2018 ( Singapore) , C. fasfes Sidabalok & Bruce 2018 ( Indonesia) ( Sidabalok & Bruce 2018a). However, the new species can be distinguished from those species by lateral margin of uropodal exopod having a more continuous row of PMS (vs uropodal exopod lateral margin with widelyspaced and acute robust setae). Moreover, C. khamensis sp. nov. can be separated from the allopatric species C. bruscai Bruce & Olesen, 2002 by the head not being produced and overriding the antennular bases; and the inferior margins of pereopods 6 and 7 are smooth (vs head weakly produced and overriding the antennular bases; inferior margins of pereopods 6 and 7 serrate in C. bruscai ).

Etymology. The epithet is taken from the type locality.

Figures

FIGURE 2. Cirolana khamensis sp. nov., holotype male (6.5 mm, PSUZC–CR0288-01), A, D; paratype male (8.4 mm, PSU- ZC–CR0288-02),B, E); paratype female (7.8 mm, PSUZC–CR0288-02), C; paratype male (7.9 mm, PSUZC–CR0288-02), F, G, H. A, dorsal view; B, lateral view; C, head; D, frons; E, pleon; F, antennula; G, antenna peduncle; H, penial opening, sternite 7.

FIGURE 3. Cirolana khamensis sp. nov., paratype male (7.9 mm, PSUZC-CR2088-02). A, left mandible; B, distal part of mandible; C, maxillule; D, maxilla E, maxilliped; G, maxilliped endite.

FIGURE 4. Cirolana khamensis sp. nov., paratype male (7.9 mm, PSUZC-CR2088-02). A, pereopod 1; B, dactylus of pereopod 1; C, mesial view of pereopod 1; D, pereopod 2; E, pereopod 4.

FIGURE 5. Cirolana khamensis sp. nov., paratype male (7.9 mm, PSUZC-CR2088-02), A, lateral of pereopod 6; B, mesial view of pereopod 6; C, lateral view of pereopod 7; D, mesial of pereopod 7.

FIGURE 6. Cirolana khamensis sp. nov., paratype male (7.9 mm, PSUZC-CR2088-02). A–E, pleopods 1–5 respectively.

FIGURE 7. Cirolana khamensis sp. nov., paratype male (7.9 mm, PSUZC-CR2088-02).A, uropod; B, ventral view of uropodal exopod; C, pleotelson; D, uropodal exopod apex.