Most anemones attach to a firm substratum by the aboral end but some inhabit soft bottoms and do not attach. The periphery of the gastrovascular cavity is partitioned by abundant, longitudinal, sheetlike mesenteries which greatly increase the surface area for absorption of food and its subsequent intracellular digestion. The central region of the cavity is unpartitioned and is the site of extracellular digestion. The free edges of the mesenteries border the central region and secrete hydrolytic enzymes into it. There is no polymorphism or alternation of generations and the medusa is absent.
Anemones are hermaphroditic.
Aiptasia pallida is a common anemone on floating docks, oyster reefs, and other hard substrata in shallow water in the southeastern United States. It is best to use dark individuals if they are available. Another species, Metridium senile , is widespread and occurs in northeastern North America and in northern Europe. It inhabits shallow, subtidal water and lives attached to rocks. It is larger than Aiptasia and does not harbor zooxanthellae.