Asymmetrorbione, Boyko, 2003

Boyko, Christopher B., 2003, A new genus and species of bopyrid isopod (Crustacea, Isopoda, Bopyridae, Orbioninae) parasitic on Sicyonia (Crustacea, Decapoda, Penaeoidea) from New Caledonia, Zoosystema 25 (4), pp. 593-600 : 595

Asymmetrorbione n. gen.

Orbione – Chopra 1923: 444-447 (in part). — Markham 1994: 236 (non Orbione Bonnier, 1900 ).

TYPE SPECIES. — Asymmetrorbione drepanopleon n. sp.

ETYMOLOGY. — The generic name is given to emphasize the posterior asymmetry of the included species, in combination with the name of the type genus for the subfamily Orbioninae .

DIAGNOSIS. — Female: one side of pereon and pleon distinctly longer than other; head broad, weakly produced with strong anterior lamina. Maxilliped with thin distally rounded spur; upper margin subovate with rounded, non-articulating palp. First oostegite proximal lobe ovate, distal lobe subtriangular, tapering and rounded, internal ridge smooth. Pereon composed of seven pereomeres, broadest across pereomere III. Coxal plates well developed on longer side, posterior two differing in shape from anterior five. Dorsolateral bosses larger on longer side. Oostegites only partly enclosing marsupium. Basis of all pereopods bearing pronounced rounded medial boss with scales on distal half. Pleon with five pleomeres plus pleotelson; pleomeres I-V with biramous pleopods and uniramous lateral plates; short side of body with reduced lateral plates; long side of body with lateral plates elongated on pleomeres I and II, shorter on III, short and round- ed on IV and V; edges and surfaces of all lateral plates smooth; pleopodal exopodites and endopodites with lightly tuberculate surfaces, uropods uniramous.

Male: head subovate, distinct from first segment of pereon. Pereomeres 3-5 broadest; all pereomeres directed laterally. Pereopods all subequal. Pleon with all segments plus pleotelson fused into single segment, tapering posteriorly with rounded tip. No midventral tubercles, pleopods or uropods.

SYSTEMATIC POSITION

This new genus appears close to Anisorbione Bourdon, 1981 in overall morphology, especially in the pronounced asymmetry of the pleon and the lateral plates, as well as the asymmetry in the development of the coxal plates on the posterior pereonal segments. The most obvious differences between the two genera are that Anisorbione females have only five pleonal segments and biramous uropods while Asymmetrorbione n. gen. females have the primitive condition of five pleomeres plus pleotelson, but uniramous uropods. Asymmetrorbione n. gen. females can be separated from those of Orbione by the pronounced asymmetry of the pleon and lateral plates (symmetrical to slightly asymmetrical in Orbione ), by the relative size of the uropods (much shorter in Asymmetrorbione n. gen.), and by the lack of tubercles on the lateral plates of Asymmetrorbione n. gen. Asymmetrorbione n. gen. can also be separated from both Anisorbione and Orbione by the extreme reduction of the coxal plates on the shorter side, which are well developed in at least the first two pereomeres of both sides in those two genera. The first oostegites of Asymmetrorbione n. gen. appear to be unique in the Orbioninae in that they have smooth internal ridges without any projections whatsoever ( Chopra [1923] described this ridge in A. kempi n. comb. as having “a large lobe and two or three smaller ones” but illustrated it as smooth and almost identical to that of A. drepanopleon n. gen., n. sp. [ Fig. 2C, D ]). Males of Asymmetrorbione n. gen. are more anteroposteriorly compact than those of either Orbione or Anisorbione , and in this resemble males of Parapenaeon Richardson, 1904 .

Figures

FIG. 2. — Asymmetrorbione drepanopleon n. gen.,n. sp., holotype 4.43 mm (MNHN-Ep 898);A, right antenna (left) and antennule (right); B, left maxilliped; C, left oostegite 1, external; D, left oostegite 1, internal; E, left pereopod 1; F, left pereopod 7. Scale bars: 0.1 mm.