Anemones, Actiniaria

Detailed introduction

Actiniaria is a large group within the phylum Cnidaria and class Anthozoa, commonly known as sea anemones . They typically live solitary lives (unlike stony corals which form aggregate skeletons). Their bodies consist of a foot disc, column, oral disc, and tentacle crown . They prey on small crustaceans, fish larvae, and plankton using nematocysts , and can also form complex ecological relationships with symbiotic algae or organisms (such as clownfish, hermit crabs, and shrimp).

Ecology and Biology

• Feeding: The tentacles are covered with thorn sacs, which have an adhesive/paralyzing effect; they are mostly used to ambush predators , but can also ingest organic detritus.

• Symbiosis: Some genera and species live in symbiosis with zooxanthellae to enhance their energy acquisition; they also often establish mutually beneficial relationships with fish, shrimp, and crabs (such as the clownfish-anemone system).

• Reproduction: It can be sexual (spermatogenic eggs/larvae) or asexual (fission, transverse fission, basal plate budding, etc.); it has strong dispersal and regeneration capabilities.

Morphology and Recognition

Sea anemones lack calcified skeletons and have soft body walls; their tentacles are arranged radially symmetrically around the oral disc, and sometimes they have a distinct pharyngeal groove and internal septum. They come in a variety of colors, from translucent to brightly colored; some species have parapodia/warts on their body surface to help attach debris for camouflage.

Body size and lifespan

• Body length/tentacle span: from micro-species less than 1 cm to large species with a tentacle span of 30–60 cm or more (such as giant sea anemones).

• Lifespan: Mostly perennial , they can survive for many years or even longer in stable environments; they have significant regenerative capabilities.

Distribution and Habitat

Widely distributed in oceans worldwide , from the intertidal zone to the deep sea; commonly found on various substrates such as reef surfaces, sandy bottoms, seagrass beds, cave entrances, and wharf pile foundations, they attach through foot plates , and a few types are partially buried in sand or mud or can temporarily move freely.

Ecological significance and threats

• Ecological role: Small predator and sanctuary provider (the "home" for symbiotic fish and shrimp).

• Threats include: coastal pollution, eutrophication, rising sediment load, bottom trawling and harvesting, and abnormal sea surface temperatures.

IUCN: Anemones is a higher-level entry, and its specific conservation status needs to be assessed at the species level ; this site's overview is treated as Unassessed (NE) .