Rhopalione kali, Ahyong & Boyko, 2019

Ahyong, Shane T. & Boyko, Christopher B., 2019, Rhopalione kali sp. nov., first known epicaridean parasite on the Malaysian pinnotherid crab, Serenotheres besutensis (Serène, 1967), Zootaxa 4590 (2), pp. 283-288 : 284-286

Rhopalione kali sp. nov.

( Fig. 1 )

isopod parasite.— Serène 1967: 819.

Rhopalione sp.— Ahyong & Ng 2005: 124.— An et al. 2014: tab. 1.

Type material. HOLOTYPE: MNHN-IU-2013-19983 , non-ovigerous female (bl 4.00 mm, bw 3.95 mm), from abdominal cavity of Serenotheres besutensis ( Serène, 1967) (cl 7.0 mm, cw 9.0 mm, from Lithophaga sp. ex Platygyra sp., MNHN IU-2008-11151 , MNHN B.21778 ), Perhentian Besar , South China Sea , east coast of Peninsular Malaysia, 05°55’N, 102°45’E, 4 m, coll. R. and P. Serène, 22 July 1965 . ALLOTYPE: MNHN-IU-2013-19984 , mature male (bl 2.70 mm, bw 1.23 mm), collected together with holotype .

Description. Female holotype ( Fig. 1 A–H). Length 4.00 mm; width (pereomeres 4, not including extended coxal plates) 3.95 mm; head length 0.85 mm; head width 1.39 mm. Body nearly straight ( Fig. 1A, B ), subcircular in outline but wider than long (0.9 × width) when including coxal plates, distortion angle less than 5°; all somites distinct.

Head subquadrate, separated from pereon, 1.6 × wider than long, anterior and posterior margins convex, lateral margins almost straight; wide frontal lamina. Eyes absent. Antennules ( Fig. 1C ) of 3 articles each, antennae of 5 articles each, both visible dorsally, neither with setae. Maxilliped ( Fig. 1D ) longer than wide; broad non-articulated palp with short, recurved, digitate apex; plectron short, slender, straight. Barbula ( Fig. 1D, E ) laterally with outer elongate, smooth, slender falcate projection and inner short acute projection, shallowly concave medially.

Pereon nearly straight ( Fig. 1A ). Pereomeres dorsally distinct, produced laterally into blunt, rounded lobes; widest at pereomere 4; margins straight or weakly curved, mid-dorsal bosses or projections absent; irregularly-shaped dorsolateral bosses and coxal plates on all 7 pereomeres, fusion of dorsolateral bosses and coxal plates in posterior 2 pereomeres. Oostegites completely enclosing brood pouch, strongly vaulted ventrally, not protruding beyond anterior margins of body, not visible dorsally. Oostegite 1 ( Fig. 1G, H ) longer than wide; anterior lobe rounded, with shallow emargination, longer than distal lobe; internal ridge with few irregular slender digitations and rounded lobes ( Fig. 1H ); posterior lobe with acute, slightly recurved distal projection on margin. Oostegite 5 ( Fig. 1B ) posterior margin fringed with fixed setae. Pereopods isomorphic, subchelate ( Fig. 1F ).

Pleon short ( Fig. 1A ), 5 pleomeres, all dorsally distinct, each with lateral plates produced into slender, distally rounded lobes, similar in size and shape to corresponding 5 pairs of biramous pleopods ( Fig. 1B ). Uniramous uropods ( Fig. 1A ) similar in size and shape to pleopods and adjacent lateral plates of pleonite 5.

Male allotype ( Fig. 1 I–L). Length 2.70 mm; width (at pereomeres 5) 1.23 mm; head length 0.43 mm; head width 0.73 mm. Body elongate, fusiform, slightly curved, distortion angle 16°, length 2.2 × width; all somites distinct.

Head transversely ovate in dorsal view, about twice as long as pereomere 1 (along midline) ( Fig. 1I ); anterior margin broadly curved, almost straight medially; posterior margin broadly curved; eyes present but weakly pigmented. Antennules of 3 articles each, antennae of 5 articles each, both with terminal setae ( Fig. 1K ).

Pereomeres 1–7 ( Fig. 1I ) subequal in length, lateral margins rounded, posterior margins straight or at most weakly sinuous, mid-dorsal bosses or projections absent; pereomere 1 0.9 × width of pereomere 2; pereomeres 2–4, 6, 7 subequal in width, narrower than pereomere 5; midventral projections absent (Fig, 1J). Pereopods isomorphic in size and shape, subchelate ( Fig. 1L ).

Pleon ( Fig. 1I ) broadly tapering to rounded general outline; pleomeres distinct, distal margins produced as slen- der tapering lobes, posteriorly recurved, apices blunt; pleopods 1–5 ( Fig. 1J ) bulbous, uniramous. Pleotelson ( Fig. 1I, J ) deeply bifurcate posteriorly.

Colouration. Completely faded except for traces of eye pigmentation in male allotype.

Host. The type material of the new species was hosted by the holotype of the pinnotherid crab Serenotheres besutensis ( Serène, 1967) , itself hosted by the bivalve mollusc, Lithophaga sp. ( Mytilidae ) collected from the scleractinian coral, Platygyra sp. (originally recorded by Serène 1967 as Coeloria sp.) ( Merulinidae ).

Etymology. The species is named for the similarity in outline of the female with her extended coxal plates to that of Kali, the Hindu Goddess of death and time, who is often depicted holding swords in her multiple arms. The name is given as a noun in apposition.

Distribution. Perhentian Besar, eastern Peninsular Malaysia; 4 m depth. Note that the latitude of Perhentian Besar originally cited by Serène (1967) was incorrectly given as 60°55’N, rather than 05°55’N.

Remarks. Rhopalione kali sp. nov. is the fifth species of the genus to be formally recognized. Of the named species of Rhopalione , R. kali closely resembles R. uromyzon in several features, sharing similarly blunt, dorsolateral bosses and coxal plates in females that are partially fused on the posterior segments, and clear demarcations between all pereomeres and pleomeres. The two species are readily separated, however, by shape of the head in females (subquadrate with a straight frontal laminar margin in R. kali , ovate with a medially emarginate frontal laminar margin in R. uromyzon ), female body proportions (slightly wider than long in R. kali versus longer than wide in R. uromyzon ), and in males, the pleotelson (bilobate in R. kali , undivided in R. uromyzon ). Females of R. kali are readily separated from those of R. atrinicolae and R. incerta by the blunt instead of sharply pointed coxal plates and sharply pointed lateral plates of the pleomeres, respectively; and from R. sinensis by the presence of the maxilliped palp (absent in R. sinensis ) and subquadrate (versus ovate) head. Males of R. kali readily differ from those of R. atrinicolae by the straight instead of distinctly angular posteromedian margins of pereomeres 2–4, and from R. sinensis in the straight instead of medially concave anterior margin of the head. The male of R. incerta is currently unknown.

Rhopalione kali is the first bopyrid to be recorded from a host species of the genus Serenotheres Ahyong & Ng, 2005 . Species of Rhopalione are seldom collected, and with regard to host, may be species-specific, or at least genus-specific ( An et al. 2014). The most frequently reported species, R. sinensis from East Asia, infests Arcotheres sinensis ( Shen, 1932) ( Kuo et al. 2018) . Rhopalione uromyzon infests the Persian Gulf endemic, Discorsotheres spondyli ( Nobili, 1905) ( Ahyong 2018) , and R. atrinicolae from New Zealand infests Nepinnotheres atrinicola ( Page, 1983) ( Page 1985) . The host of R. incerta from Madagascar remains unknown ( Bonnier 1900). In addition to the named species of Rhopalione , an undescribed species is known from South Australia as a parasite of Discorsotheres subglobosus ( Baker, 1907) ( Ahyong 2018) , and an undetermined form, R. pelseneeri Pérez, 1920 (nomen nudum) from a pinnotherid obtained from a bivalve, Arca sp., was reported from Lombok, Indonesia ( Pérez 1920). The close geographic proximity of the known localities of “ R. pelseneeri ” and R. kali invites the question of whether they could be conspecific. Unfortunately, Pérez (1920) provided no further information on either the isopod or the host crab. Given the locality and the strongly taxonomically correlated host associations exhibited by pinnotherid crabs, however, the pinnotherid host, being from Arca sp., was probably a species of Arcotheres Manning, 1993 ( Ahyong & Ng 2007). As such, Pérez’s “ R. pelseneeri ” is almost certainly not referable to R. kali , which is hosted by Serenotheres besutensis , which itself infests the burrowing bivalve, Lithophaga sp. ( Mytilidae ) ( Ahyong & Ng 2005). Although “ R. pelseneeri ” might be referable to R. sinensis , which also infests a species of Arcotheres , R. sinensis has so far been confirmed only from East Asia (mainland China, Hong Kong, Taiwan). “ Rhopalione pelseneeri ” may therefore represent an undescribed species.

Keys to both sexes of the species of Rhopalione are presented below. The key to females includes all described species but note that the key to males excludes R. incerta .

Figures

FIGURE 1. Rhopalione kali sp. nov., Perhentian Besar, Malaysia: A–H, holotype female, length 4.00 mm, MNHN-IU-2013- 19983; I–L, allotype male, length 2.70 mm, MNHN-IU-2013-19984. A, I, dorsal view; B, J, ventral view; C, K, left antennule and antenna, ventral view; D, left maxilliped with lateral lobe of barbula, external view; E, barbula, median region; F, L, right pereopod 1 of female and male, respectively; G–H, left oostegite 1, external and internal views. Scale: A–B = 1.0 mm; C–J =0.5 mm; K–L = 0.25 mm.