Rhopalione racemus Boyko & Williams 2024, n. sp.
Creators: name: Boyko, Christopher B.
name: Williams, Jason D.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Bopyridae
Rhopalione
Rhopalione racemus

description: Rhopalione racemus n. sp.
(Figs 8; 9)
urn:lsid:zoobank.org:act: 91BC048C-A4A0-4959-A322-504403BE1E36
“large parasitic Isopod (Epicarid)” – Hale 1927: 174 [ex Pinnotheres subglobosus Baker, 1907 (now Discorsotheres subglobosus (Baker, 1907), Gulf St. Vincent, South Australia; specimen examined herein]. — Silas & Alagarsiwami 1967: 1191 [reference to Hale’s findings].
“the isopod mentioned by Hale” – Page 1985: 201 [mention].
? “an undescribed species of Rhopalione ” – Poore et al. 2002: 124 [see Remarks below].
Rhopalione sp. – McDermott 2009: 792, table 2 [list]. — An et al. 2014: 2, table 1 [list]. — Ahyong 2018: 557 [ex Discorsotheres subglobosus (Baker, 1907), Gulf St. Vincent, South Australia]. — Williams et al. 2023: 533 [list].
TYPE MATERIAL. — Holotype. Australia • ovigerous ♀ (8.9 mm TL), from under pleon of ♀ Discorsotheres subglobosus (Baker, 1907) (10.5 mm CL, 11.7 mm CW), ex Equichlamys bifrons (Lamarck, 1819) (Pectinidae Rafinesque, 1815); South Australia, Port Willunga; 25.II.1990; N. Holmes leg.; SAM C16386.
Allotype. Australia • mature ♂ (3.8 mm TL), collected with holotype; South Australia, Port Willunga; 25.II.1990; N. Holmes leg.; SAM C16386.
Paratype. Australia • 1 mature ♀ (6.4 mm TL; male not present), from under pleon of female D. subglobosus (7.6 mm CL, 8.6 mm CW), ex E. bifrons; South Australia, Gulf St. Vincent; no date; A. Zietz leg.; SAM C1397.
ETYMOLOGY. — The specific name, racemus, is a Latin noun meaning a bunch of grapes, which the shapes of the pleopods and lateral plates resemble; it is used in apposition.
DESCRIPTION
Female
Holotype (Figs 8A, B, 9 A-H). Length 8.9 mm; maximal width at posterior margin of pereomere 46.9 mm (not including coxal plates); head length 1.5 mm; head width 1.8 mm. Body nearly straight (Fig. 8A, B), subcircular in outline but slightly longer than wide when including coxal plates, not distorted; all segments distinct. Head ovate, separated from pereon, slightly wider than long, anterior and posterior margins convex, lateral margins rounded; wide frontal lamina. Eyes absent. Antennules (Fig. 9A) of two articles each, antennae (Fig. 9A) of five articles each, both visible dorsally, few setae distally. Maxilliped (Fig. 9C) longer than wide; narrow non-articulated palp with blunt apex; spur elongate, slender, distally actute. Barbula (Fig. 9B) laterally with outer elongate, smooth, slender falcate projection and inner short acute curved projection; shallowly convex medially. Pereon nearly straight (Fig. 8A). Pereomeres dorsally distinct, produced laterally into blunt, rounded lobes; widest at pereomere 4; margins weakly curved, mid-dorsal bosses or projections absent; irregularly shaped dorsolateral bosses and coxal plates on all seven pereomeres, dorsolateral bosses and coxal plates in posterior pereomeres not fused. Oostegites completely enclosing brood pouch (Fig. 8B), strongly vaulted ventrally, protruding beyond anterior margins of body, visible dorsally. Oostegite 1 (Fig. 9D, E) longer than wide; anterior lobe rounded, subequal in length to distal lobe; internal ridge with numerous irregular slender digitations (Fig. 9E); posterior lobe with acute, triangular distal projection on margin. Oostegite 5 (Fig. 9F) posterior margin fringed with setae. Pereopods isomorphic, subchelate (Fig. 9G, H); small curved dactylus, propodus ovate, carpus and merus fused, ischium and basis tubular, relatively short (Fig. 9G). Pleon short (Fig. 8A; 9F), five pleomeres, all dorsally distinct, each with lateral plates produced into short, distally rounded lobes, similar in size and shape to corresponding five pairs of biramous pleopods (Fig. 9F). Uniramous uropods (Fig. 9F) similar in size and shape to pleopods and adjacent lateral plates of pleomere 5.
Male
Allotype (Figs 8C; 9 I-L). Length 3.8 mm; maximal width at posterior margin of pereomere 4 1.6 mm; head length 0.4 mm; head width 0.9 mm. Body elongate, fusiform, straight, length 2.4 × width; all segments dorsally and ventrally distinct (Figs 8C; 9I). Head transversely ovate in dorsal view, about two-thirds as long as pereomere 1 (along midline) (Fig. 8C); anterior and posterior margins nearly straight; eyes absent. Antennules (Fig. 9J) of three articles each, antennae (Fig. 9J) of five articles each, both with terminal setae. Pereomeres 1-7 (Figs 8C; 9I) subequal in length, lateral margins subquadrate, posterior margins straight or at most slightly concave; pereomeres 1 and 7 subequal in width, 0.85 × width of pereomere 2; pereomeres 2-6 subequal in width; midventral projections absent (Fig. 9I). Pereopods isomorphic in size and shape, subchelate; dactyli of anterior pair longer than others, setose; propodus ovate, with setae along edge corresponding to region meeting distal end of dactylus; carpus and merus fused, end of carpus with small setae; ischium and basis tubular, bases longer on posterior pereopods (Fig. 9K, L). Pleon (Figs 8C; 9I) broadly tapering to rounded general outline; pleomeres dorsally and ventrally distinct, distal margins produced, posteriorly slightly recurved, lateral margins rounded, medioventral tubercles absent; pleopods 1-4 (Fig. 9I) reniform, pleopods 5 rounded, uniramous. Pleotelson (Fig. 8C, I) slightly indented posteriorly.
REMARKS
Females of Rhopalione racemus n. sp. can be distinguished from all other species in the genus by the shape of the pleopods and lateral plates which are short and rounded; females of all other species have markedly elongate pleopods and lateral plates. The specimens reported by Hale (1927) are the paratypes examined and designated as such herein. We consider the specimens cited by Ahyong (2018; SAM C12813) that were collected from same host species in a known locality (Gulf St. Vincent) for R. racemus n. sp. to be this species, although they were not examined for this study.
Poore et al. (2002) noted that “an undescribed species of Rhopalione has been identified from Australia by J. Markham” but this has not been described; it may be conspecific with R. racemus n. sp. but given the lack of information on the locality and host, this is far from certain.
description: Published as part of 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, pp. 149-175 in Zoosystema 46 (7) on pages 167-169, DOI: 10.5252/zoosystema2024v46a7, http://zenodo.org/record/10863451