Rhopalione atrinicolae Page, 1985

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 : 163-165

Rhopalione atrinicolae Page, 1985

( Fig. 6 )

Rhopalione atrinicolae Page, 1985: 199-201 , figs 10, 11 (ex Pinnotheres atrinicola Page, 1983 (now Nepinnotheres atrinicola (Page, 1983)) , New Zealand). — McLay 1988: 329 [mentioned erroneously as a gill parasite]. — Markham 1990: 562 [mention]. — Taylor & Morrison 2008: 194, table 1 [ex N. atrinicola , New Zealand]. — McDermott 2009: 788, 790, 792, tables 1, 2 [mention, list]. — An et al. 2014: 2, table 1 [list], 4 [key to species]. — Ahyong & Boyko 2019: 283 [mention], 286, 287 [mention, key to species]. — Williams et al. 2023: 532 [list].

TYPE MATERIAL EXAMINED. — New Zealand • ovigerous (with epicaridium larvae) holotype ♀ (10.0 mm TL), from pleon of non-ovigerous female Nepinnotheres atrinicola Page, 1983 (14.6 mm CL, 15.8 mm CW), ex Atrina zelandica (Gray, 1835) ( Pinnidae ); Whangarei Harbour between High Island and mainland; 0-1 m; 13.V.1982; B. Dobson, G. Miles, C. Turbott & C. Worthington leg.; NMNZ Cr.3022 • Mature allotype ♂ (5.5 mm TL), collected with holotype; Whangarei Harbour between High Island and mainland; 0-1 m; 13.V.1982; B. Dobson, G. Miles, C.Turbott & C. Worthington leg.; NMNZ Cr.3022 • 1 ovigerous (with epicaridium larvae) paratype ♀ (9.1 mm TL), mature paratype ♂ (5.0 mm TL), non-ovigerous paratype ♀ (9.0 mm TL), mature paratype ♂ (4.3 mm TL), from pleon of non-ovigerous female N. atrinicola Page, 1983 (two hosts: 15.2 mm CL, 12.2 mm CW & unmeasurable CL (damaged), 17.8 mm CW (parasites separated from hosts so not possible to match them), ex A. zelandica (Gray, 1835) ( Pinnidae ); Hauraki Gulf, channel between Takatu and Kawau Islands, 23.IX.1971; M.V. Ikatere on R/V Grace, leg.; NMNZ Cr.3090.

OTHER MATERIAL EXAMINED. — New Zealand • 4 mature ♀ (10.6- 12.1 mm TL), from stomach of Mustelus antarcticus Günther, 1870 (Chondrichthyes, Triakidae ); Hauraki Gulf; c. 36.73°S, 175.05°E, 24.VII.1949; J. Morton leg.; NIWA 160626.

DESCRIPTION (modified from Page 1985)

Female

Body nearly straight, ovate in outline, longer than wide; all segments distinct. Head subquadrate, separated from pereon, wider than long, medially indented, anterior and posterior margins convex, lateral margins rounded; thin frontal lamina. Eyes present or absent. Antennules of three articles each, antennae of five articles each, both setose, neither visible dorsally. Maxilliped longer than wide; broad non-articulated palp, with distal recurved lobe, apex rounded; plectron short, slender, straight. Barbula with pair of smooth, slender falcate projections laterally, deeply concave medially. Pereon nearly straight. Pereomeres dorsally distinct, produced laterally into tapered, rounded lobes; widest at pereomere 5; margins straight or weakly curved, mid-dorsal bosses and projections absent; irregularly-shaped dorsolateral bosses and distally acute coxal plates on all seven pereomeres. Oostegites completely enclosing brood pouch, strongly vaulted ventrally, protruding beyond anterior margins of body, visible dorsally. Oostegite 1 longer than wide; anterior lobe rounded, with shallow emargination, subequal to distal lobe; internal ridge smooth; posterior lobe with acute, nearly straight distal projection on margin. Oostegite 5 posterior margin fringed with setae. Pereopods isomorphic, subchelate. Pleon short, five pleomeres, all dorsally distinct, each with lateral plates produced into slender, distally rounded lobes, similar in size and shape to corresponding five pairs of biramous pleopods. Uniramous uropods similar in size and shape to pleopods and adjacent lateral plates of pleomere 5.

Male

Body elongate, fusiform, straight, length 3.0 × width; all segments distinct. Head transversely ovate in dorsal view, shorter than pereomere 1; anterior margin broadly curved, almost straight medially; posterior margin broadly curved; eyes present. Antennules of three articles each, antennae of five articles each, both with terminal setae. Pereomeres 1-7 subequal in length, lateral margins rounded, 1-4 with posterior margins concave; all pereomeres subequal in width; midventral projections absent. Pereopods isomorphic in size and shape, subchelate. Pleon with subquadrate outline; pleomeres distinct, distal margins rounded, posteriorly recurved, apices blunt; pleopods 1-5 bulbous, uniramous. Pleotelson rounded posteriorly.

REMARKS

The description of Page (1985) is comprehensive, and his illustrations are sufficient to recognize the species; the female ( Fig. 6A ) and male ( Fig. 6B ) paratype specimens (NMNZ Cr. 3090) were examined and photographed. All female specimens of R. atrinicolae have distally acute coxal plates which distinguishes this species from all others in the genus. The specimens obtained from the stomach of a gummy shark, Mustelus antarcticus , are in surprisingly good condition ( Fig. 6C, D ) and match well the original description by Page (1985). Two specimens have bifid tips on some pleopods and one specimen has lateral plates with slightly crenulate edges ( Fig. 6D ). The gummy shark M. antarcticus feeds predominately on benthic crustaceans but can opportunistically feed on a wide range of species, including occasionally bivalves (e.g., Coleman & Mobley 1984; Yick et al. 2007). There do not appear to be any published records of the shark feeding on horse mussels, but to have four specimens of R. atrinicolae in its gut, it is most likely that the shark fed on one or more of these bivalves within which pea crabs parasitized by the bopyrids resided. It is unknown whether there were also specimens of the host pinnotherid in the shark’s gut; the bopyrid specimens were originally in the Dominion Museum (Wellington) but now in the NMNZ and there are no records of their host pea crabs or mussels (Mills, pers. comm.). There are previous records of pea crabs from the gut contents of bony fish ( Miller, 1967) but, to our knowledge, no records of bopyrids in any bony fish or sharks. This is surprising given that some bopyrid hosts are abundant food resources for their predators; this likely reflects an artifact of bopyrids being placed into the category of “other” during gut content analyses. These parasites may play a more important role in trophic interactions than previously thought (see Lafferty et al. 2008 for discussion of this across other parasite taxa and Sikkel & Welicky 2019 for discussion on crustacean parasites specifically).

Figures

FIG. 6. — Rhopalione atrinicolae Page, 1985 paratype specimens (A, B: NMNZ Cr. 3090) and non-type specimens (C, D: NIWA 160626): A, female, dorsal view; B, male, dorsal view. C, female, dorsal view; D, female, dorsal view, arrow shows lateral plate with slightly crenulate edge. Scale bars: A, C, D, 2 mm; B, 1 mm.