Most species are known from inshore marine environments, tidepools in particular, but a few freshwater species are also known, and some marine invertebrates harbor exo- or endosymbiotic species.
Some species are also important in aquaculture as food organisms for juvenile fish and shellfish.
Tetraselmis belongs to the flattened clade. Postulated phylogenetic position of Tetraselmis , inferred from molecular and morphological data. Branch lengths are arbitrary and do not reflect phylogenetic distance.