n. Any organism that spends part of its life-cycle (especially the larval stage) as plankton
The Century Dictionary and Cyclopedia
n. The organisms, considered collectively, that pass part of their lives in the depths of the ocean and part at or near the surface.
Word Usage
"Planktonic larvae, also known as "meroplankton" are the most common early life stage of marine invertebrates, many of whom live on the bottom as adults."