Actiniidae

Actiniidae is a family of sea anemones in the order Actiniaria, class Anthozoa, phylum Cnidaria. It includes a large and ecologically important group of sessile, polyp-form cnidarians that typically attach to hard substrates by a flat pedal disc and extend a cylindrical body with a crown of tentacles surrounding a central mouth. Like other anthozoans, members of Actiniidae lack a rigid skeleton; their soft tissue relies on cnidocytes with nematocysts to capture prey.

Most actiniids occur in marine environments from shallow subtidal zones to offshore habitats, with a cosmopolitan distribution in temperate and tropical seas. They are found on rocky shores, coral reefs, and on soft sediments, often forming solitary individuals or aggregations in crevices, crests, or tidepools. They are opportunistic carnivores that feed on small invertebrates, using nematocysts to immobilize prey.

Reproduction in Actiniidae is variable. Species may reproduce sexually, releasing eggs and sperm into the water column, and producing planula larvae that settle as new polyps. Many species can also reproduce asexually by pedal laceration, budding, fragmentation, or fission, enabling rapid colony expansion.

Some Actiniidae form symbiotic relationships with photosynthetic algae (zooxanthellae) or other organisms, which can contribute to nutrition in well-lit habitats. The family is taxonomically diverse, with many genera and species, and its composition has been reshaped by molecular studies. Actiniidae species are sometimes kept in aquariums and are of interest in studies of cnidarian physiology and venom.