Allokepon monodi Bourdon 1967

Allokepon monodi (Bourdon, 1967)

(Fig. 2)

Portunicepon monodi Bourdon, 1967: 112 –116, figs. 4–6. Allokepon monodi Markham, 1982: 357.

Material examined. Infesting Portunus pelagicus, Hainan province, 20° 0 2ˏ N, 110° 35ˏ E, 29 April 1980, CIEP 800401, Ψ. Infesting Portunus trituberculatus (Miers), Qukou, Hainan province, 20° 0 0ˏ N, 110° 30ˏ E, 4 November 1990 CIEP 901101, 2 Ψ. Infesting Thalamita sp. Linchen. Intertidal sand, 4 December 1990, CIEP 901201, Ψ, ɗ.

Descriptive note. Reference female (CIEP 901201). Length 9.14 mm (excluding uropods), maximal width 8.4 mm, head length 2.13 mm, head width 2.67 mm. Body outline round, almost symmetry (Fig. 2 A, B).

Head bilobate, frontal lamina extending beyond both sides of head. Eyes absent (Fig. 2 A). Antennae of 3 and 5 articles (Fig. 2 C), basis two articles stout. Maxilliped (Fig. 2 D) with prominent non-articulating, curved and setose palp; plectron short, pointed. Barbula (Fig. 2 E) with two falcate projections on each side, outer pairs larger than inner pairs, a pair of cone-shaped tubercles on the middle region.

Pereon broadest across pereomere 3. Prominent middorsal projections on last two pereomeres. Brood pouch entirely covered by oostegites. Oostegite 1 (Fig. 2 F, G) smoothly rounded anteriorly, posterior edge with setae; internal ridge slightly crenulate. Pereopods similar in structure except increasing in length posteriorly.

Pleon of six pleomeres, first five with biramous pleopods and lateral plates, all digitate and abound of tubercles on ventral surface (Figs. 2 B, H). Uniramous uropods similar in structure to lateral plates of pleomere 5, but longer than lateral plates.

Reference male (CIEP901201). Length 2.69 mm, maximal width across pereomere 4, 0.80 mm, head length 0.19 mm, pleonal length 1.59 mm. Pleon narrower than pereon, all segments distinct (Fig. 2 I, J).

Head semicircular, broader than long. No eyes. Head and first pereomere distinctly separated (Fig. 2 I). Antenna 1 of 3 articles, antenna 2 of 5 articles, each setose distally.

Pereomeres deeply separated. Prominent midventral tubercles on each pereomere. Pereopods all about same size and structure (Fig. 2 J).

Pleon of six segments, midventral tubercles on pleomere 1. Pleomeres 1–5 with tuberculiform pleopods (Fig. 2 J), final pleomere produced into two backward projections, with obscure tubercular structure similar to pleopods indicating uropods.

Immature female (CIEP901101). Proportionately much narrower, body segments distinctly separated (Fig. 2 K, L). Eyes absent. Antennae of 3 and 5 articles. Oostegites rudimentary, and brooch pouch open. Last two pereomeres with middorsal projections. Pleopods slender, slightly digitate, absence of tubercles on ventral surface of pleopods and lateral plates.

Remarks. Bourdon (1967) described Portunicepon monodi from a female specimen parasitic on Stenorhynchus seticornis (Herbst). Markham (1982) established the genus Allokepon and transferred P. monodi to Allokepon. This is the second record of the species, and the present females are very similar to the holotype (Bourdon, 1967), although the head is distinctly bilobate in the present specimens. The male of A. monodi has not earlier been reported and this is the first report of P. trituberculatus as host for parasitic isopods.

Distribution and hosts. In Senegal, on Stenorhynchus seticornis; in China, on Portunus pelagicus, Portunus trituberculatus and Thalamita sp.