Three new species of shell-boring Dipolydora (Annelida: Spionidae: Polydorini) from the South China Sea and the Gulf of Thailand, Vietnam, with comments on the modified spines in posterior notopodia and sperm morphology in polydorins.

Abstract

Three species of tube-dwelling polydorins (Annelida: Spionidae: Polydorini) from China have been reported for the South China Sea to date. Three new species of shell-boring Dipolydora are described and illustrated in the present study based on new material collected in the Gulf of Thailand and Nha Trang Bay, Vietnam. Dipolydora echinata sp. nov. and D. spinosa sp. nov. have awl-like spines in addition to capillary chaetae in the posterior notopodia, and cup-shaped pygidia with only dorsal incision. Dipolydora vietnamita sp. nov. has only capillary chaetae in the posterior notopodia, and three-lobed pygidium with one ventral lobe and two smaller dorsal lobes. Gradual transformation of capillary chaetae along the body and the morphology of modified spines in the posterior notopodia of polydorin spionids are briefly discussed. Gamete morphology is considered an underestimated trait used for the identification of spionids.