from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Any of various organisms that spend part of their life cycle, usually the larval or egg stages, as plankton.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any organism that spends part of its life-cycle (especially the larval stage) as plankton
from 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.
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.
Examples of meroplankton include larvae of sea urchins, starfish, clams, crustaceans, worms and most fish.
Within the plankton, holoplankton are those that spend their entire life cycle in the plankton, while meroplankton are those organisms that are only planktonic for part of their lives (usually the larval stage), and then move into the nekton or a benthic habitat.
Post-transport ballast water contains high densities of both holoplankton, organisms such as dinoflagellates and jellyfish that spend their entire life as plankton, and meroplankton, the temporary larval stages of crustaceans, worms, and fish.