ABSTRACT
Having passed through the planktonic stage (prolonged in planktotrophic and short in lecithotrophic larvae), the larvae of invertebrates get ready for settlement and further development. The transition from planktonic (pelagic) to periphytonic existence (see Section 1.1) is the key moment in the life cycle of organisms inhabiting hard surfaces of natural and artificial origins. Indeed, in many species, the metamorphosis into an adult is possible only on a hard surface. In some cases, in the larvae of those species whose adults are attached, metamorphosis may also end during the free-swimming stage, according to laboratory observations (Berrill, 1931; Chia and Bickell, 1978; Cloney, 1978). In these cases, the organisms do not establish contact with the substrate, and, if they were in the sea milieu, they surely would be quickly eliminated.
