The slug-like larva of Phoronis ovalis swims for about 4 days, creeps on the sea-bed for 3 to 4 days, then bores into a carbonate floor.[27][28] Nothing is known about three species. The remaining species develop free-swimming actinotroch larvae, which feed on plankton. The actinotroch is an upright cylinder with the anus at the bottom and fringed with cilia. At the top is a lobe[1] or hood, under which are: a ganglion, connected to a patch of cilia outside the apex of the hood;[7] a pair of protonephridia(smaller and simpler than the metanephridia in the adult);[1] the mouth; and feeding tentacles that encircle the mouth.[7] After swimming for about 20 days, the actinotroch settles on the seabed and undergoes a catastrophic metamorphosis (radical change) in 30 minutes: the hood and larval tentacles are absorbed and the adult lophophore is created round the mouth, and both now points upward; the gut develops a U-bend so that the anus is just under and outside the lophophore.[1] Finally the adult phoronid builds a tube.[7]