Invertebrates
Tube Anemone
Ceriantharia · also called tube anemones, cerianthids
A crown of tentacles spreads gently above the sand, and the moment a shadow passes too close, the entire structure vanishes into the sediment below, a tube anemone retreating into a tube built from silk found in no other animal on the reef.
Overview
The tube anemone, order Ceriantharia, is a burrowing cnidarian found across soft-sediment ocean floor habitat worldwide. Its uniquely constructed tube, built from a type of stinging cell found nowhere else in nature, and its lightning-fast withdrawal set it apart from the true sea anemones it superficially resembles.
A look-alike with its own set of rules
Despite wearing a crown of tentacles that could easily be mistaken for a true anemone at a glance, the tube anemone plays by an entirely different set of biological rules, from its unusual tube-building silk down to the double ring of tentacles no true anemone possesses.
Status
Not Evaluated — present across suitable soft-sediment ocean floor habitat worldwide, with no documented widespread decline.
Tube Anemone: common questions
Is a tube anemone actually a sea anemone?
No, despite the common name and a broadly similar appearance, the tube anemone belongs to an entirely separate taxonomic order from true sea anemones, a distinction supported by real differences such as its unique tube-building silk and its two separate rings of tentacles rather than the single ring typical of true anemones.
What is a tube anemone's tube made of?
A tube anemone constructs its tube using specialised threads called ptychocysts, a type of modified stinging cell that is unique to this group and found in no other cnidarian, spinning them into a fibrous casing that houses and protects the animal's soft body within the sediment.
How fast can a tube anemone hide?
A tube anemone can retract into its protective tube with striking speed when threatened, disappearing from view almost instantly, a much faster withdrawal than the comparatively slow retreat typical of true sea anemones responding to disturbance.
Where does the tube anemone live?
A tube anemone lives buried within soft ocean-floor sediment in coastal and deeper waters worldwide, keeping only its crown of feeding tentacles extended above the surface while the majority of its body remains protected within the tube below.