Two new species of Sigambra (Annelida, Pilargidae) from the Andaman coast and the Gulf of Thailand

Abstract

Two species of Pilargidae, Sigambra pakbaraensis sp. nov. and S. sirilukae sp. nov. are described from different coasts of Southern Thailand (Andaman Sea and the Gulf of Thailand). Both species belong to the subgroup of Sigambra which lack ventral cirri at chaetiger 2 and have capillary notochaetae. Sigambra pakbaraensis sp. nov. is described from the Andaman coast and can be distinguished from other species in the genus by the occurrence of the first dorsal hook at chaetiger 8, the presence of capillaries in notopodia, and 14 pharyngeal papillae. Sigambra sirilukae sp. nov. is described from the Gulf of Thailand and it is clearly distinguished from all other species in the genus by having 12 pharynx papillae, an elongate median antenna with a large ceratophore, dorsal hooks from middle chaetigers, and up to five capillary notochaetae from anterior most chaetigers (4-5). Molecular phylogenetic analyses, based on cytochrome oxidase subunit I (COI) and mitochondrial genes 16S, indicate S. pakbaraensis sp. nov. clusters within Sigambra Müller, 1858. Pores on the dorsal and ventral cirri of both species are herein described for the first time for the genus. An updated key to species of Sigambra from the Indo-Pacific region is also provided.