sperm are formed into little balls called spermatophores by specialist organs. When dispersed, they become amoeboid and make their way through the body wall of an adult worm before fertilising eggs in the metacoel. The resulting zygotes make their way out through the nephridiopores and become planktonic larvae. They may be brooded as an egg mass in the lophophoral cavity for a period. The larva is known as an actinotroch and was thought for a long time to be an adult organism in its own right and given the generic name Actinotrocha sabatieri. 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. In the process, the gut is bent double into the U-shape typical of this phylum. Asexual reproduction also takes place, usually by transverse fission, and may result in groups of individuals clustered in close proximity to each other, sometimes tangled together. References External links information & images Phoronids Animals described in 1889