Metamorphosis in larvae of the temperate sea cucumber Australositchopus mollis

Abstract

Summary Holothurian larvae that feed on phytoplankton during development exhibit a dramatic metamorphosis involving extensive reorganisation of all larval tissue before adopting a benthic existence and assuming the juvenile form. During this process in the temperate sea cucumber Australostichopus mollis the combined axohydrocoel differentiated into the coelomic lining of the buccal podia and radii, both appearing early. Although podia primordia appeared shortly after, the podia themselves appeared later. This process appeared associated with differentiation of oral cavity tissue and formation of the water vascular ring canal. Oral cavity tissue was displaced temporarily but was not evidence of axial torsion. Tissue differentiation of the reorganised alimentary canal occurred post settlement and the mouth of the benthic juvenile opened well after settlement to initiate feeding. These larvae exhibit a variable and protracted transition to the benthic juvenile form rather than an abbreviated sequence of progressive anatomical events as in indirect non-feeding developers.