an organism that spends only a part of its life cycle as a member of the plankton community (e.g., the barnacle or starfish, in which only the larval stages are planktonic)
See meroplankton in American Heritage Dictionary 4
(mĕrˌə-plăngkˈtən)
noun
Any of various organisms that spend part of their life cycle, usually the larval or egg stages, as plankton.