Rhopalione rusa, Boyko & Williams, 2024

Boyko, Christopher B. & Williams, Jason D., 2024, New records of bopyrid parasites (Crustacea, Isopoda, Epicaridea) of pea crabs (Crustacea, Decapoda, Pinnotheridae) with descriptions of two new species of Rhopalione Pérez, 1921 and a review of the genus, Zoosystema 46 (7), pp. 149-175 : 169-172

Rhopalione rusa n. sp.

( Figs 10 ; 11 )

urn:lsid:zoobank.org:act:C780B367-B63A-495A-9951-717DBE2F0549

“bopyrids under pleon” – Ng & Ahyong 2022: 173 [ex ZRC 2019.0534; specimens examined herein].

“unidentified bopyrid” [of Arcotheres similis ] – Williams et al. 2023: 533 [list].

TYPE MATERIAL. — Holotype. Singapore • ovigerous ♀ (6.8 mm TL), from left side of pleon of female Arcotheres similis (Bürger, 1895) ( ZRC 2019.0534; 6.0 mm CL, 7.6 mm CW), ex Modiolus philippinarum Hanley, 1843 ( Mytilidae Rafinesque, 1815 ); off Changi Beach, intertidal area next to Carpark 7, near ferry terminal; 22.IV.2019; S. K. Tan et al. leg.; ZRC 2023.0259.

Allotype. Singapore • Mature ♂ (4.1 mm TL), collected with holotype; off Changi Beach, intertidal area next to Carpark 7, near ferry terminal; 22.IV.2019; S. K. Tan et al. leg.; ZRC 2023.0260

Paratype. Singapore • 1 ovigerous ♀ (5.5 mm TL; male not present), from right side of pleon of female A. similis (ZRC 2019.0534; 5.6 mm CL, 7.5 mm CW), ex Modiolus philippinarum Hanley, 1843 ( Mytilidae ); off Changi Beach, intertidal area next to Carpark 7, near ferry terminal; 22.IV.2019; S. K. Tan et al. leg.; ZRC 2023.0261.

ETYMOLOGY. — The species is named after the type locality of Changi Beach which, in 1604, was originally called “Tanjong Rusa” (tanjong meaning cape and rusa being Malay for deer which could refer to the extinct Indian muntjac ( Muntiacus muntjak (Zimmerman, 1780)) or the once thought extinct Sambar deer (Rusa unicolor Kerr, 1792). The change of name from Tanjong Rusa to Tanjong Changi occurred between 1604 and 1828 ( Gibson-Hill 1954; Borschberg 2017; https://eresources.nlb.gov.sg/infopedia/articles/ SIP_245_ 2004-12-15. html). The name is a noun in apposition.

DESCRIPTION Female Holotype ( Figs 10 A-C; 11A-G). Length 6.8 mm; maximal width at posterior margin of pereomere 4 5.0 mm (not including extended coxal plates); head length 0.9 mm; head width 1.4 mm. Body nearly straight ( Fig. 10A, B ), subcircular in outline but approximately as wide as long when including coxal plates, not distorted; all somites distinct. Head ovate, separated from pereon, 1.6 × wider than long, anterior and posterior margins convex, lateral margins rounded; wide frontal lamina. Eyes absent. Antennules ( Fig. 11A ) of three articles each, antennae ( Fig. 11A ) of five articles each, both visible dorsally, few setae distally. Maxilliped ( Fig. 11D ) longer than wide; broad non-articulated palp with blunt apex; spur elongate, recurved, distally triangular ( Fig. 11D inset), covered by large round accessory lobe. Barbula ( Fig. 11B ) laterally with pair of elongate, smooth, broad falcate projections, distally tapering; shallowly convex medially. Pereon nearly straight ( Fig. 10B ). Pereomeres dorsally distinct, produced laterally into blunt, rounded lobes; widest at pereomere 4; margins weakly curved, mid-dorsal bosses or projections absent; ovoid dorsolateral bosses on pereomeres 1-6, round on pereomere 7, all dorsolateral bosses distinctly separated from lateral portion of pereomeres; ovoid coxal plates on all seven pereomeres, shorter than dorsolateral bosses on pereomeres 1-4, longer than dorsolateral bosses on pereomeres 5-7, dorsolateral bosses and coxal plates in posterior pereomeres not fused. Oostegites completely enclosing brood pouch ( Fig. 10C ), strongly vaulted ventrally, not protruding beyond anterior margins of body, not visible dorsally. Oostegite 1 ( Fig. 11E, F ) longer than wide; anterior lobe rounded, larger than distal lobe; internal ridge with few irregular low digitations ( Fig. 11F ); posterior lobe with acute, triangular distal projection on margin. Oostegite 5 ( Fig. 11C ) posterior margin fringed with setae. Pereopods isomorphic, subchelate ( Fig. 11E, G ), small curved dactylus, propodus ovate with scales around region that meets tip of dactylus, carpus and merus triangular, ischium and basis tubular, carpus with distal setae and scales. Pleon short

( Fig. 10B ), five pleomeres, all dorsally distinct, each with lateral plates produced into long, slender, distally rounded lobes, similar in size and shape to corresponding five pairs of biramous pleopods ( Figs 10B ; 11C ); endopodites with small basal swelling (observable in lateral view), decreasing in size on posterior pleomeres. Uniramous uropods ( Fig. 10B ; 11C ) similar in size and shape to pleopods and adjacent lateral plates of pleomere 5.

Male

Allotype ( Figs 10D ; 11 H-M). Length 4.1 mm; maximal width at pereomeres 2-5 1.3 mm; head length 0.4 mm; head width 0.8 mm. Body elongate, fusiform, straight, length 3.2 × width; all somites dorsally and ventrally distinct ( Figs 10D ; 11H ). Head transversely ovate in dorsal view, about half as long as pereomere 1 (along midline) ( Fig. 10D ); anterior and posterior margins weakly convex; irregularly shaped eyes. Antennules ( Fig. 11I ) of three articles each, antennae ( Fig. 11I ) of five articles each, both with terminal setae. Pereomeres 1-7 ( Figs 10D ; 11H ) subequal in length, lateral margins rounded, posterior margins straight or at most slightly concave; pereomeres 2-5 subequal in width; pereomeres 1, 6, 7 narrower, subequal in width; midventral projections absent ( Fig. 11H ). Pereopods isomorphic in size and shape, subchelate, dactyli of anterior two pairs longer than others, all dactyli with setae, propodus ovate, with setae along edge corresponding to region that meets distal end of dactylus, carpus and merus triangular, end of carpus with small setae and scales, ischium and basis tubular ( Fig. 11H, J, K ). Pleon ( Figs 8C ; 9I ) broadly tapering with triangular general outline; pleomeres dorsally and ventrally distinct, distal margins splayed, posteriorly slightly recurved, lateral margins rounded; pleomeres 1-4 with medioventral tubercles ( Fig. 11H ); pleopods 1-5 ( Fig. 11H, M ) reniform, uniramous, with minute setae in concave region ( Fig. 11M ). Pleotelson ( Figs 10D ; 11H ) narrow anteriorly, widening posteriorly, indented posteromedially.

REMARKS

Females of Rhopalione rusa n. sp. are most similar to R. racemus n. sp. in the shape of the pereomeres, which are greatly inflated laterally, forming a kind of barbell shape; however, the females differ in the form of the pleopods and lateral plates which are long and slender in R. rusa n. sp. but short and broad in R. racemus n. sp. Additionally, the barbula of females of R. rusa n. sp. bears two subequal lobes whereas that of females of R. racemus n. sp. have the outer lobe much longer than the inner. Males of the two species are also similar with both having five pairs of reniform pleopods but R. rusa n. sp. has midventral tubercles on pleomeres 1-4 whereas R. racemus n. sp. lack midventral tubercles. Rhopalione racemus n. sp. is known only from Discorsotheres subglobosus collected in South Australia (Temperate Australasia) vs Rhopalione rusa n. sp., which is only known from Arcotheres similis collected in Singapore (Central Indo-Pacific) (see Spalding et al. 2007 for discussion of marine ecoregions).

The material of Rhopalione cited by Ng & Ahyong (2022) comprises the type series as designated herein. The holotype female left approximately four puncture holes from the mouthparts in ventral pleomeres 1 and 2 (toward midline) of the host; the paratype female left puncture holes in ventral pleomeres 1 and 2 (toward midline) of the host.

Figures

FIG. 10. — Rhopalione rusa n. sp. holotype (ZRC 2023.0259) and allotype (ZRC 2023.0260) specimens: A, ventral view of host pinnotherid Arcotheres similis (Bürger, 1895) with Rhopalione sp. in situ on left side of pleon (posterior end of male shown by arrow);B, holotype female, dorsal view; C, holotype female,ventral view; D, allotype male, dorsal view. Scale bars: A, 2 mm; B-D, 1 mm.

FIG. 11. — Rhopalione rusa n. sp. holotype (ZRC 2023.0259, A-G) and allotype (ZRC 2023.0260,H-M) specimens (ZRC 2019.0534): A, left antennae; B, barbula, left side;C, dorsal view of terminus of pleon showing fifth pleomere with lateral plates on both sides and biramous pleopod shown only on right side and uropods; D, left maxilliped,outer view;inset shows inner view of anterior lobe and spur obscured by lobe of maxilliped (*); E, left oostegite 1 and pereopod 1, outer view; F, left oostegite 1, inner view; G, left pereopod 7; H, ventral view;I, left antennae; J, right pereopod 1; K, right pereopod 1, close-up of dactyl and propodus; L, right pereopod 7; M, pleomere showing pleopod 4 on right side and mid-ventral tubercule. Abbreviations: En, endopod; Ex, exopod; Lp, lateral plate; Uro, uropods. Scale bars: A, G, L, M, 100 µm; B, D-F, 250 µm; C, H, 500 µm; J-K, 50 µm.

FIG. 8. — Rhopalione racemus n. sp. holotype and allotype specimens (SAM C16386): A, holotype female, dorsal view; B, holotype female, ventral view; C, allotype male, dorsal view. Scale bars: A, B, 2 mm; C, 1 mm.

FIG. 9. — Rhopalione racemus n. sp. holotype (A-H) and allotype (I-L) specimens (SAM C16386): A, left antennae; B, barbula; C, left maxilliped, with base of barbular lobes shown; D, left oostegite 1, outer view; E, left oostegite 1, inner view; F, pereomere 7 and pleon, ventral view; G, left pereopod 1 and coxal plate; H, left pereopod 7; I, ventral view; J, right antennae, oral cone and maxilliped; K, right pereopod 1; L, left pereopod 7. Abbreviations: CP, coxal plate; IL, inner barbular lobe; Max, maxilliped; OL, outer barbular lobe; Or, oral cone. Scale bars: A, G, H, 100 µm; B, D, E, I, 500 µm; C, 250 µm; F, 1 mm; J-L, 50 µm.