Plankton may also be categorized according to how much of the life cycle is spent in the plankton. Holoplankton , for example, are planktonic their entire lives, while meroplankton spend only a part of their life cycle in the water column, usually as a larval stage. The planktonic larval stages of invertebrate animals often look very different from the non-planktonic adults. After a period of hours to weeks to months in the plankton, larvae settle on a surface and metamorphose into their more familiar adult forms, such as the cup coral pictured to the left. Animals such as these that live on or associated with the sea floor are called benthic.
Size is another way to categorize plankton.
Finally, plankton can be classified by the relationships among organisms. A list of common invertebrate phyla found in the local plankton is at the bottom of this page, with links to appropriate pages. For more information about plankton specifically, and invertebrates in general, see our page of references . After each plankton collecting trip, we brought the samples back to the lab to view them under a microscope. For this reason, we have focused on four themes concerning how organisms in the plankton relate to their habitat, and to each other.