Rhopalione incerta ( Bonnier, 1900 )

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 : 158-159

Rhopalione incerta ( Bonnier, 1900)

Orbione incerta Bonnier, 1900: 61 , 379 [list]. — Danforth 1970: 14 [mention].

Orbione (?) incerta Bonnier, 1900: 222 [list], 282-284, text fig. 50 [host unknown, Madagascar]. — Nierstrasz & Brender à Brandis 1923: 66 [list]. — Page 1985: 199 [mention].

Rhopalione incerta – Pérez 1920a: 1617 [mention]. — Nierstrasz & Brender à Brandis 1923: 68, 69 [mention]. — Bourdon 1976: 353 [mention]. — Page 1985: 201 [mention]. — Markham 1990: 562 [mention]. — Kensley 2001: 226 [list]. — An et al. 2014: 2, table 2 [list], 4 [key to species]. — Ahyong & Boyko 2019: 283, 286 [mention], 287 [key to species]. — Williams et al. 2023: 533 [list].

O. incerta – Richardson 1904a: 857 [discussion of generic placement]; 1904b: 52 [discussion of generic placement]. — Chopra 1923: 419, 446, 447 540 [discussion of generic placement]. — Cattley 1938: 240 [discussion of generic placement].

[ Orbione] incerta – Shiino 1949: 53 [mention].

“ Orbione? penei ” [sic] – Markham 1990: 563 (error for Orbione (?) incerta ).

TYPE MATERIAL EXAMINED. — Madagascar • holotype ♀ (4.35 mm, damaged), ex “ Pilumnus ” [sic] (= Pinnotheridae sp. indet.); NossiLava; 1896; Bastard leg.; MNHN-IU-2024-3186 (= Ep125).

REDESCRIPTION

Female (based on extant parts of holotype and description and figure in Bonnier (1900); measurements extrapolated from extant body segments).

Body length 7.68 mm, maximal width 9.19 mm, head length 1.53 mm, head width 2.85 mm. Pereon essentially straight, right side coxal plates more produced laterally. All body regions and pereomeres distinctly segmented. Head broader than long, strongly produced with frontal lamina equal to approximately one-twelfth length of head, pereomere 1 median not obscured by head; barbula with two thin projections. Eyes absent. Antennule of three articles, antenna of five articles. Maxilliped with palp. First oostegite proximal lobe ovate, distal lobe subtriangular with median acute projection, internal ridge with number of small projections. Pereon of seven pereomeres, broadest across pereomere 5, gradually tapering anteriorly and posteriorly; pereomeres 1-3 with slightly convex posterior margins, 4-7 with concave posterior margins. Coxal plates as large, bilobed lobes on pereomeres 1-5, clearly separated from pereomeres and with tapered distal margin on right side of body. Dorsolateral bosses on pereopods 1-5 large, oblong, and clearly demarcated with right ones slightly larger than left. Pereomeres 1-6 lacking clearly demarcated median region and tergal projections. Oostegites enclosing marsupium. Pereopods all subequal, posterior pairs slightly longer. Pleon with five distinct pleomeres plus pleotelson; posterior margins of all pleomeres concave and sinuous. Pleomeres 1-5 with biramous pleopods and uniramous lateral plates; endopodites and exopodites of all pleopods elongate and tapered, subequal in size; lateral plates strongly produced and distally tapered to subacute tips; edges and surfaces of all lateral plates smooth; uropods uniramous, subequal in shape and size to pleopods and lateral plates.

Male

Unknown.

KEY TO SPECIES OF RHOPALIONE PÉREZ, 1920 (BASED ON CHARACTERS OF MALES AND FEMALES)

l Females with short, rounded pleopods and lateral plates .......................................... Rhopalione racemus n. sp.

— Females with elongate pleopods and lateral plates ........................................................................................ 2

2 Females with pleopods and lateral plates acute distally ..... Rhopalione incerta ( Bonnier, 1900) , male unknown

— Females with pleopods and lateral plates rounded distally ............................................................................ 3

3 Females with coxal plates acute distally ......................................................... Rhopalione atrinicola Page, 1985

— Females with coxal plates rounded distally ................................................................................................... 4

4 Males with large, reniform pleopods and midventral tubercles ..................................... Rhopalione rusa n. sp.

— Males with rounded pleopods, midventral tubercles absent ......................................................................... 5

5 Males with pleopods displaced laterally ................................................... Rhopalione sinensis Markham, 1990

— Males with pleopods close to median of pleon ............................................................................................. 6

6 Male with pleotelson deeply bifurcated ............................................ Rhopalione kali Ahyong & Boyko, 2019

— Male with pleotelson small, rounded, not bifurcated .................................. Rhopalione uromyzon Pérez, 1920

REMARKS

The holotype specimen jar contains the same kind of label as found in many of the vials of the R. uromyzon syntypes and was in the house of Dr Pérez at the time of his death. Although its rediscovery is fortuitous, the holotype is in very poor condition. The head, oostegites, pereopods, lateral plates and pleopods of the left side, and both uropods are absent, presumably as the result of loss after dissection. However, the salient features of the pereomeres and pleomeres that remain allow for verification of Bonnier’s (1900) illustrated features. Although Bonnier (1900) wrote a fairly lengthy text description, he was somewhat imprecise in his descriptions of most of the appendages and provided an illustration of only the dorsal aspect of the whole specimen. It is clear, however, that R. incerta is indeed a Rhopalione , despite statements to the contrary by some other authors (e.g. Nierstrasz & Brender à Brandis 1923), and that it is most closely related to R. atrinicolae from New Zealand. Characters that the two species share include the maxilliped with distinct palp, oostegite 1 not produced over cephalon, and outer lobe of bilobed coxal plates on pereomeres 1-4 distally acute or subacute. The two species differ in the shape of the head (distinctly wider in R. incerta ), the degree of acute prolongation of outer lobe of bilobed coxal plates on pereomeres 1-4 (acute in R. atrinicolae vs. subacute in R. incerta ), internal ridge of oostegite 1 (smooth in R. atrinicolae vs. with several small digitations in R. incerta ), shape of the lateral plates and pleopods (distally rounded in R. atrinicolae vs. acute in R. incerta ), and the uropods (biramous in R. atrinicolae vs. uniramous in R. incerta ). This last character may not be a valid one to separate the species, given its variability in R. uromyzon .

Although Bonnier (1900) indicated that the host of R. incerta was a species of “ Pilumnus ”, the host pleon is still present in the vial with the holotype and is clearly that of a female pinnotherid.