Onkokepon beibuensis An & Yu & Li 2006, n. sp.

Onkokepon beibuensis n. sp. (Figs 5, 6)

Material examined: Holotype. ♀, EL627001, Infesting Leucosia longibranchia Shen & Chen, Beibu Gulf Stn. 6270, 19°30ʹN, 106°30ʹE, 33.5 m, Zhengang Fan, coll., 13 May 1960. Allotype. ♂, EL627002, Beibu Gulf Stn. 6270, 19°30ʹN, 106°30ʹE, 33.5 m, Zhengang Fan, coll., 13 May 1960. Paratypes. 1 ♀ EL627003, ♂, EL627004; Beibu Gulf Stn. 6270, 19°30ʹN, 106°30ʹE, 33.5 m, Zhengang Fan, coll., 13 May 1960; 2 ♀, EL624801, 2 ♂, EL624802, Beibu Gulf Stn. 6248, 20°30ʹN, 107°30ʹE, 37 m, Fuzeng Sun, coll., 14 February 1960.

Description of female holotype: Length (not including uropods) 8.5 mm, maximal width 4.9 mm, head length 2.0 (including frontal lamina), pleon length 1.5 mm. All body segments distinct, almost symmetrical (Fig. 5A).

Head deeply bilobate frontly, fringed by well­developed, digitate, tubercular frontal lamina, whose length exceeds half of head, its width completely along edge of head and three large tubercles with elaborated small tubercles on the anterior margin. Eyes absent. Antennae 1 with 4 articles, 1 terminal seta, and antennae 2 with 6 articles, 2 terminal setae (Fig. 5B). Barbula with two digitate lateral projections on each side, medially unornamented, outer sides of projections with prominent digitate margin, inner sides smooth (Fig. 5C). Maxilliped with slightly curved, non­articled, pointed, setose palp and sharply pointed plectron (Fig. 5D, E).

Pereon broadest across pereomere 3, gradually tapering on each side posteriorly. Coxal plates absent. No middorsal projections on pereon. Dorsolateral bosses on pereomeres 1–4, prominent tergal projections on pereomeres 2–4. Last 3 pereomeres with small tubercles on the joint between pereomeres and pereopods. White strip on middorsal region of pereon. Oostegites completely enclosing brood pouch, oostegite 1 smoothly rounded anteriorly, with complex digitate internal ridge, setae on posterior margin and sharp posterolateral point (Fig. 5F, G). Oostegites 2–4 with smooth edges, oostegite 5 posteriorly setose, oostegite 4 largest (Fig. 5H). Pereopods 1–6 essentially alike except progressively longer posteriorly, pereopod 7 merus as long as ischium (Fig. 5I, J).

Pleon of 6 pleomeres, first 5 bearing biramous pleopods and elongate digitate lateral plates, last 3 lateral plates almost as long as respective exopod (Fig. 5 L–P). Endopodite of pleopod produced into thick and blunt pointed distally, margin of endopodite 3 slightly digitate, others entire (Fig. 5 L–P; Fig. 5K). Terminal pleomere with long uniramous uropods outer sides with slightly digitate margins and inner sides with deeply indented margins (Fig. 5A).

Description of male allotype: Length 2.8 mm, maximal width, across pleomere 2, 0.6 mm, head length 0.3 mm, head width 0.5 mm, pleonal length 1 mm. All body regions and segments distinct (Fig. 6A, B).

Head suboval, eyes small. Antenna 1 with 3 articles, distal tuft of 3 setae, antenna 2 with 7 articles, distal tuft of about 7 setae, second segment bearing 1 seta, third segment bearing 2 setae (Fig. 6C, D).

Pereomeres almost equally wide, with rounded margins, lacking midventral projections. Pereopod 1 largest, others similar, but propodi of posterior pereopods attached more proximally than that of first pereopod (Fig. 6 E–G).

Pleon of 6 pleomeres, first 5 with tuberculiform pleopods, midventral projection absent, last pleomere produced into 2 rounded divergent points. No uropods.

Etymology: The specific name beibuensis refers to the Beibu Gulf, the type locality of this species.

Variations: The paratype females agree in all respects with the holotype.

Remarks: Oostegite 4 (Fig. 5H) of Onkokepon beibuensis with another parasitic isopods (unidentified) on the proximate portion of oostegite 4. The two new species can be differentiated based on the maxilliped palp, the posterolateral point of oostegite 1 and the shape of the frontal lamina of female. Another significant difference is the presence of midventral projections of pleomeres and articulated dactyli in males of Onkokepon articulatus. The two­segmented dactyli are not reported in any other bopyrid isopods, it is so unusual that Onkokepon articulatus can distinguish from other known bopyrid isopods.