Sea Anemones

Details

Actiniaria (sea anemones) are anthozoan cnidarians that are typically solitary and lack a calcareous skeleton. The body comprises a pedal disc, column, oral disc and a crown of tentacles armed with nematocysts for prey capture. Many species form mutualisms with zooxanthellae and/or symbiotic fishes and crustaceans (e.g., anemonefishes and shrimps).

Ecology & Biology

• Feeding: ambush predators using nematocysts to immobilize small crustaceans, larvae and fish; detrital particles may supplement diet.

• Symbiosis: some host Symbiodiniaceae while others rely entirely on heterotrophy; iconic partnerships include anemonefish–anemone systems.

• Reproduction: sexual (spawning/planulation) and asexual (fission, pedal laceration, budding); strong regenerative capacity.

Identification

No rigid skeleton; soft body with radially arranged tentacles, sometimes with verrucae for debris adhesion. Colours range from translucent to vivid. Internal mesenteries and siphonoglyphs are diagnostic in taxonomy.

Size & Longevity

• Length/tentacle span: from sub‑centimetre species to large forms with 30–60+ cm spans.

• Life: generally long‑lived with notable regenerative abilities.

Range & Habitat

Occurs in all oceans, from intertidal zones to the deep sea; attaches to rock, rubble, sand, seagrass and artificial substrates via the pedal disc. Some species partially bury or can slowly relocate.

Role & Threats

• Ecological roles: small predators and habitat providers for symbiotic fishes/shrimps.

• Threats: coastal pollution, eutrophication, sedimentation, bottom‑trawling and marine heatwaves.

IUCN: this is a high‑level overview; conservation status is species‑specific. Marked here as Not Evaluated (NE) for the overview entry.