Onkokepon articulatus, An & Yu & Li, 2006

An, Jianmei, Yu, Haiyan & Li, Xinzheng, 2006, Description of a new genus and two new species of Ioninae (Iso- poda: Epicaridea: Bopyridae) parasites of Leucosiidae (Decapoda: Brachyura) from Beibu Gulf, Zootaxa 1186, pp. 57-68 : 59-64

Onkokepon articulatus n. sp. ( Figs 1–4 )

Material examined. Holotype: ♀, EL627901, infesting Leucosia longibranchia Shen & Chen, Beibu Gulf Stn. 6279, 19°45ʹN, 106°00ʹE, 23.5 m, Xiutong Ma , coll., 5 December 1959 . Allotype: ♂, EL627902, infesting Leucosia longibranchia Shen & Chen, Beibu Gulf Stn. 6279, 19°45ʹN, 106°00ʹE, 23.5 m, Xiutong Ma , coll., 5 December 1959 . Paratypes: Infesting Leucosia longibranchia Shen & Chen. 1 ♀, EL619801, 1 ♂, EL619802, Beibu Gulf Stn. 6198, 20°45ʹN, 109°00ʹE, 35 m, Fuzeng Sun , coll., 16 July 1960 ; 1 ♀ immature, EL623601, Beibu Gulf Stn. 6236, 20°30ʹN, 108°00ʹE, 41.5 m, Fuzeng Sun coll., 15 July 1960 ; 1 ♀, EL620001, Beibu Gulf Stn. 6200, 20°15ʹN, 109°00ʹE, 34.5 m, Fuzeng Sun coll., 15 April 1960 ; 1 ♀, EL620002, Beibu Gulf Stn. 6200, 20°15ʹN, 109°00ʹE, 32.5 m, Fuzeng Sun , coll., 13 July 1960.

Infesting Leucosia unidentata de Haan. 1 ♀, EL626401, 1 ♂, EL626402, Beibu Gulf Stn. 6264, 18°30ʹN, 107°00ʹE, 62 m, Fuzeng Sun coll., 25 May 1960.

Description of female holotype: Length (not including uropods) 9.7 mm, maximal width 5.7 mm, head length 1.6 mm, head width 2.4 mm, head including front lamina length 2.3 mm, pleon length 2.2 mm, uropods length 3.9 mm. All body segments distinct, slightly asymmetrical ( Fig. 1A, B ).

Head deeply bilobate, white with radial yellow stria, covered anteriorly by well­developed, finely undulate, tuberculate and setiferous triangular frontal lamina. Frontal lamina extending beyond sides of head, its median part about half as long as head. Posterior edge of head curved. Eyes absent. Antenna 1 of 3 articles, bearing 2 terminal setae; antenna 2 of 5 articles with 1 terminal seta ( Fig. 1C ). Barbula with two complex digitate lateral projections on each side, outer sides of projections with prominent digitate margins, inner sides seldom digitate, middle region irregular ( Fig. 1D ). Maxilliped smooth with curved, articulated, pointed, setiferous palp and sharply pointed plectron ( Fig. 1E, J ).

Pereon broadest across pereomere 3, gradually tapering on each side posteriorly ( Fig. 1B ). Coxal plates absent. No middorsal projections on pereon. Dorsolateral bosses on pereomeres 1–4, tergal projections on pereomeres 2–4 prominent, those on pereomere 1 small. Small tubercles on the joint between pereomeres and pereopods on left side of last 3 pereomeres. Oostegites completely enclosing brood pouch, oostegite 1 round anteriorly, spiny laterally, with deeply digitate internal ridge, setose margin posteriorly and blunt posterolateral point ( Fig. 1F, G ). Oostegite 2 with setae along anterior margin, and oostegites 3–5 posteriorly setose, oostegite 4 largest. Pereopods essentially alike except progressively longer posteriorly ( Fig. 1H, I ).

Pleon of 6 pleomeres, of which 2–4 serrated, first 5 bearing biramous pleopods and elongate digitate lateral plates, last 3 lateral plates almost as long as respective exopods ( Fig. 2 A–E). Endopodites of pleopods rudimentary to thick and round patches, of various shapes. Margins of endopodites 1 and 5 entire, 2 and 4 slightly digitate, 3 deeply digitate. Terminal pleomere with long uniramous uropods, their outer sides with almost smooth margins and inner sides deeply indented ( Fig. 1A ).

Description of male allotype: Length 2.6 mm, maximal width across pleomere 4, 0.6 mm, head length 0.2 mm, head width 0.4 mm. All body regions and segments distinct ( Fig. 3A, B; Fig. 4A ).

Head suboval, posteriorly fused with first pereomere. Eyes small ( Fig. 3A, B ). Antenna 1 of 3 articles with 2 setae distally ( Fig. 3C ; Fig. 4B ), antenna 2 of 7 articles with distal tuft of about 5 setae, second segment bearing 2 setae, third segment bearing 2 setae ( Fig. 3D ; Fig. 4C ).

Pereomeres 2–5 almost equally wide, truncate margins. Pereomeres 5–7 with midventral elevated borders. Pereopod 1 largest, pereopod 2 the second largest; others similar, dactyli much larger on first 2 peropods than on the other 5, dactyli of pereopods evidently two­segmented ( Fig. 3E, F, G ; Fig. 4D ).

Pleon of 6 pleomeres, first 5 with tuberculiform pleopods, first 2 with midventral projections, last pleomere produced into 2 rounded divergent points, each bearing sparse tubercles. Uropods absent ( Fig. 3B ; Fig. 4E ).

Description of immature female (EL623601): Proportionately narrower than adult, segments of pleomeres less distinctly separated ( Fig. 2F ). Head subcircular, frontal lamina short, antennae extending beyond margin of frontal lamina, pereomeres without dorsolateral bosses, and tergal projections rudimentary, lateral plates of pleomeres with short and smooth margins, exopodites of pleopods long, narrow and digitate, endopodites of pleopods small globe­shaped; uropods similar to exopodites.

Etymology: The specific name articulatus refers to the articulated palp of the maxilliped of the females.

Variation: Females paratype agree in all respects with the holotype except that most paratypes lack radial yellow stria on their heads, and one female paratype has the posterior margin of the head cuspate (EL626401). One male paratype differs from the allotype in having its pereomere 1 as wide as its head and distinct posterior border of the head (no fusion with segment 1; EL626402) ( Fig. 3H ).

Figures

FIGURE 1. Onkokepon articulatus, n. sp. Holotype female, EL627901. A, dorsal view. B, dorsal view (except pleon). C, right antennae. D, barbula. E, right maxilliped, external view. F, left oostegite 1, external view. G, left oostegite 1, internal view. H, right pereopod 1. I, right pereopod 7. J, palp of right maxilliped. Scale = 2 mm for A, B; 0.4 mm for C; 1.10 mm for D; 1.54 mm for E; 1.83 mm for F, G; 0.76 mm for H, I; 0.57 mm for J.

FIGURE 2. Onkokepon articulatus, n. sp. A–E, Holotype female, EL627901. F, paratype immature female EL623601. A, right pleopod 1 and lateral plate (A–E: endopodites in grey). B, right pleopod 2 and lateral plate. C, right pleopod 3 and lateral plate. D, right pleopod 4 and lateral plate. E, right pleopod 5 and lateral plate. Scale = 2 mm for A–E; 1.55 mm for F.

FIGURE 3. Onkokepon articulatus, n. sp. A–G, Allotype male, EL627902. H, paratype male, EL626402. A, dorsal view. B, ventral view. C, left antennae 1. D, left antennae 2. E, left pereopod 1. F, left pereopod 2. G, left pereopod 3. H, dorsal view of paratype male. Scale = 1 mm for A; 0.72 mm for B; 0.11 mm for C, D; 0.23 mm for E–G; 0.68 mm for H. (B–G drawn according to photograph of SEM).

FIGURE 4. Onkokepon articulatus, n. sp. Allotype, EL627902, photograph by means of SEM. A, ventral view. B, two pairs of antennae. C, last three segments of antennae 2. D, first three pereopods show two­segmented dactyli. E, ventral view of pleon. Scale = 0.6 mm for A; 54.2 um for B; 9.9 um for C; 120 um for D; 217 um for E.