Viviparity of larvae, a new type of development in phoronids (Lophophorata: Phoronida)

Abstract

A new type of phoronid development, viviparity of larvae, has been discovered in a new phoronid species that lives as a commensal of digging sand shrimps in Vostok Bay, the Sea of Japan. The embryos develop in the mother’s trunk coelom up to the young larva stage. During development, embryos increase in size twice and probably obtain nutriment from the mother’s coelomic fluid. Spawning occurs by young larvae, which are released through nephridiopores. The new type of development is described in a phoronid that has a small body size but a high fertility, producing large amounts of extremely small eggs. The combination of viviparity and large number of eggs increases the number of competent larvae that can undergo metamorphosis in the burrows of shrimps.