 The actinotroch larva is transparent and has a ring of ciliated tentacles just behind the mouth, a straight gut and an anus at the posterior end.Metamorphosis is very rapid and in the course of half an hour, new tentacles appear and the body is transformed.The metasomal sac protrudes from the ventral surface and turns inside out, with the posterior end of the worm uniting with the anterior end while the previous ventral region becomes the new posterior end.