Apocepon leucosiae, Yu & Li, 2006

Yu, Jianmei An Haiyan & Li, Xinzheng, 2006, A review of the genus Apocepon Nierstrasz & Brender à Brandis (Isopoda: Epicaridea: Bopyridae) parasitic on purse crabs (Decapoda: Brachyura: Leucosiidae) from Chinese waters, with description of a new species, Zootaxa 1199, pp. 1-17 : 13-16

Apocepon leucosiae sp. nov.

( Figs 7 & 8 )

Material examined

Holotype: ♀, EL600401, infesting Leucosia anatum (Herbst) , Huilian Chen, det. of host; South China Sea, Stn. 6004, 117°30’’E, 23°30’’N, 37.9 m, Weiquan Zhang , Guangzong Wu , coll., 16 November 1959 .

Allotype: ♂, EL600402, infesting Leucosia anatum ( Herbst) , Huilian Chen , det. of host; the South China Sea, Stn. 6004, 117°30’’E, 23°30’’N, 37.9 m, Weiquan Zhang , Guangzong Wu , coll., 16 November 1959.

Description of female holotype ( Fig. 7 ) (EL600401)

Head length 1.9 mm, head width 2.5 mm, maximal width across pereomere 3 6.2 mm, pereon length 6.8 mm, rami of uropods different, longest, left ramus 3.5 mm, right ramus 2.5 mm. All body segments distinct except faint boundary of 4 and 5, almost symmetrical ( Fig. 7A, B ).

Head bilobate, frontal lamina short with slightly digitate margin and narrower than head, posterior edge of head round, without eyes. Antennae extending beyond frontal lamina and observable from dorsal view, first antenna with 3 articles, second antenna with 2 terminal setae and 5 articles ( Fig. 7C ). Barbula with two pairs of digitate pointed lateral projections, digitations of outer pair more sparse than inner pair and digitations are restricted to the basal portion of the projections, median region with two points near inner pair of lateral projections ( Fig. 7D ). Maxilliped with long curved, 3 articled, rounded, setaceous palp and blunt rounded plectron ( Fig. 7E, F ).

Pereon broadest across pereomere 3, no middorsal projections on pereon, pereomeres 1, 2 and 7 narrower than other pereomeres, pereomere 3 broadest. Dorsolateral bosses on pereomeres 1–4 prominent, tergal projections on pereomeres 2–4 distinct. Oostegites completely enclosing brood pouch, oostegite 1 smoothly round anteriorly, slightly digitate near pereopod 1, with digitate internal ridge, deeply crenulate margin posteriorly and laterally, with blunt smooth posterolateral point ( Fig. 7G, H ). Oostegites 2–5 posteriorly digitate. Pereopods subequal, carpi of pereopods 1–3 subround, but carpi of pereopods 4–7 rectangle, dactyli of pereopods 6 and 7 emend into their propodi ( Fig. 7 I–K).

Pleon of 6 pleomeres, first 5 bearing biramous pleopods and digitate lateral plates ( Fig. 7 L–P), last four lateral plates long, half as long as respective exopodites. Lateral plates of pleomere 1 as long as its endopodite. Digitate margin of lateral plates and exopodite are similar. Endopodites of pleopods 1 and 2 rudimentary and almost smooth ( Fig. 7L, M ), endopodites of pleopod 5 as long as their lateral plates and digitate ( Fig. 7P ), endopodites of pleopods 3 and 4 shorter than pleopod 5 ( Fig. 7N, O ), but digitate and longer than pleopods 1 and 2. Terminal pleomere with uniramous digitate unequal uropods with blunt round distal extremity directed posteriorly ( Fig. 7A ).

Description of male allotype ( Fig. 8 ) (EL600402)

All body regions and segments distinct, head length 0.3 mm, head width 0.5 mm. Pereon length 2.3 mm, maximal width across pleon 5 1.1 mm, pleon length 1.7 mm, pleomere 1 width 0.9 mm, pleomere 5 width 0.8 mm ( Fig. 8A, B ).

Head suboval, posterior edge round, narrower than pereomere 1, eyes absent. Antennae of three and five articles, respectively, second antenna longer ( Fig. 8C, D ). Antenna 1 with tuft of 4 or 5 setae distally, second segment with approximately 2 or 3 setae, basal segment bearing 2–4 setae. Antenna 2 with 5–7 terminal setae, third and fourth segment bearing 1 or 2 setae on distal edge.

Pereon. Pereomeres 3–7 almost equally wide, all pereomeres distinctly separated. Pereomeres 4–7 with midventral projections. All pereopods similar except longer posteriorly ( Fig. 8E ).

Pleon of 6 pleomeres, first five pleopods tuberculiform, with distinct pointed tubercles on them, pleomere 1 with square midventral projection, last pleomere suboval, bilobate with shallow median indentation, without uropods ( Fig. 8F ).

Etymology The specific name leucosiae is the genitive form of host’s generic name Leucosia .

Remarks

This species is placed in the genus Apocepon on the basis of the female’s characters: short frontal lamina, rudimentary endopodites of pleopods, digitate lateral plates and pleopods. These characters distinguish Apocepon from the other bopyrid genera ( Dactylokepon and Mesocepon ) known to infest leucosiid species.

The genus Apocepon contains three species, including the new species, all of them parasites of Leucosiidae . The new species shares general characters with the other two species of Apocepon . Its male is like that of other species of Apocepon in having similar pereopods, reduced tuberculiform pleopods on lateral extensions of pleomeres, and suboval head. This new species is most similar to Apocepon digitum Stock, 1959 , especially the males of the two species, while females of the former differ from the latter by its articulated maxilliped palp, and slightly digitate frontal lamina. This new species is also distinguished from Apocepon pulcher , as the former has digitate barbula, besides the two characters above. In addition, the new species can be distinguished from the other two species in its male having midventral projections on pereomeres 4–7 and pleomere 1.

Key to species of the genus Apocepon :

1. Maxilliped with articulated palp ...................................... Apocepon leucosiae sp. nov. ­ Maxilliped with nonarticulated palp ............................................................................. 2 2. Male with pointed V­shaped pleopod 6........................................................................... .............................................. Apocepon pulcher Nierstrasz & Brender à Brandis, 1930 ­ Male with rounded U­shaped plepod 6 ......................... Apocepon digitum Stock, 1959

Acknowledgments

This study was supported by the National Science Foundation of China (No. 30500055 and 30499341) and project (03BS111) of the Shandong Province Foundation for outstanding Young Scientist. The authors would like to thank Dr. Ruiyu Liu (J. Y. Liu, IOCAS) for his guidance of the research. We are indebted to Dr. John C. Markham, Arch Cape Marine Laboratory, USA, Dr. Christopher B. Boyko, American Museum of Natural History, USA, and Dr. Ramiro Román­Contreras, Instituto de Ciencias del Mar y Limnología, Laboratorio de Carcino­parasitología of Mexico, for their kind offers of references, much helpful advice and pre­submission manuscript review. Thanks are also due to Prof. Huilian Chen (IOCAS) for her identification of hosts and Prof. Yongliang Wang and other specialists from IOCAS for their help in material collection.

Figures

FIGURE 7. Apocepon leucosiae sp. nov. Holotype, female, EL600401. A, dorsal view. B, ventral view except pleon. C, right antennae. D, barbula, right side. E, right maxilliped. F, palp of right maxilliped. G, right oostegite 1, external view. H, same, internal view. I–K, right pereopod 2, 5 and 7, respectively. L–P, right pleopods and respective lateral plates 1–5 (endopodites of pleopods in gray, lateral plates of pleopod 2 are broken artificially in figure 7M). Scale = 2.0 mm for A, B; 0.32 mm for C, F; 1.37 mm for D; 0.66 mm for E; 1.37 mm for G, H; 0.40 mm for I–K; 2.18 mm for L–P.

FIGURE 8. Apocepon leucosiae sp. nov. Allotype, male, EL600402. A, dorsal view. B, ventral view. C, left antenna 1. D, left antenna 2. E, right pereopod 3. F, ventral view of pleon. Scale = 2.0 mm for A, B; 0.09 mm for C; 0.14 mm for D; 0.40 mm for E; 1.68 mm for F.