One new species of Comesoma Bastian, 1865 (Nematoda: Araeolaimida: Comesomatidae) and redescription with molecular characterisation of Sphaerolaimus callisto Zograf, Pavlyuk, Trebukhova & Nguyen, 2020 (Nematoda: Monhysterida: Sphaerolaimidae) from the South China Sea

Abstract

Summary One new Comesoma Bastian, 1865 species and one known Sphaerolaimus species are described from the intertidal areas of a sand beach and mangrove wetland, respectively, in Beihai City, P.R. China (South China Sea) using morphological and molecular data. Comesoma sinica n. sp. is characterised by body length 2366-2925 μm, long cephalic setae 24-32 μm, cuticle without lateral differentiation, spiral amphids with 2.5 turns, bent spicules and 3.5-4.3 cloacal body diam. long, gubernaculum parallel with spicules, and males with 20 minute precloacal supplements in the form of small pores. Molecular analyses of 18S rDNA and 28S rDNA indicate that Comesoma sinica n. sp. is closely related to other Comesomatidae genera. Sphaerolaimus callisto Zograf, Pavlyuk, Trebukhova & Nguyen, 2020, which was originally described from an estuary of northern Vietnam, the South China Sea, is characterised by long spicules and vulva situated far posterior to mid-body (82% of body length from anterior extremity), and is recorded from mangrove wetlands in Beihai City. In addition, as Sphaerolaimus longispiculatus Yang, Liu & Guo, 2021 is highly similar to S. callisto in morphology, these two species should be synonymised. Phylogenetic analyses of 18S rDNA show that S. callisto is closely related to other species of Sphaerolaimus.