a1 The Laboratory, Marine Biological Association, Citadel Hill, Plymouth PL1 2PB
Young vestimentiferans, ranging from 0.15 to 10 mm in length, were examined by light and electron microscopy (SEM and TEM). The newly settled stages have a functional gut and traces of larval ciliation, which suggests that they may have developed from a planktonic trochophore stage. The larval mouth becomes an elongated siphon and the ciliated gut persists for some time after the development of the bacterial symbiosis in the trophosome. The segmentation of the body in the earliest stages is similar to that in postlarval Pogonophora, and it is concluded that Vestimentifera and Pogonophora are closely related.