Paracaesicola nanshaensisn. gen., n. sp. (Monogenea, Microcotylidae) a gill parasite of Paracaesio sordida(Teleostei, Lutjanidae) from the South China Sea

Paracaesicolan. gen., is erected herein to accommodate a new microcotylid species, Paracaesicola nanshaensisn. sp., collected from the Yongshu Reef, South China Sea. This species is the first monogenean to be recorded from the gills of Paracaesio sordida. The new species is characterized by the following features: (i) haptor short, with clamps arranged in two equal bilateral rows; (ii) testes numerous, arranged in two roughly alternating longitudinal rows, extending into the haptor; (iii) genital atrium armed with 16 robust spines, which are vertically arranged on top of the sausage shaped muscular male copulatory organ; and (iv) single vagina, bottle-shaped, with a distinctly bulbous vaginal atrium. The terminals of the reproductive system discriminate Paracaesicolan. gen. from all other genera in the Microcotylidae. Molecular phylogenetic analyses, based on partial 28S rDNA, places Paracaesicola nanshaensisn. sp. within the microcotylid clade, but its sequence differs from all known available microcotylid sequences.