Some of the more important groups in this regard are the diatoms and dinoflagellates . These two groups are considered part of the Kingdom Protista. The key characteristics of protists are that they are unicellular and have a nucleus. Much of the phytoplankton is consumed by copepods . These small crustaceans, often referred to as the 'insects of the sea' are are extremely abundant in the oceans both in terms of numbers and biomass.
Copepods are important components of the food web.
They are soft-bodied carnivores that capture their prey with the aid of tentacles or sticky cells. The common term 'jellyfish' refers to a different taxonomic group of organisms that resemble ctenophores in being jelly-like. These are the scyphozoans of the phylum Cnidaria . These animals also capture their prey with the aid of tentacles. However, they also possess stinging cells called nematocysts that disable the prey with a 'barbed hook' and poison.