Tube-dwelling anemones or ceriantharians look very similar to sea anemones but belong to an entirely different class of anthozoans. They are solitary, living buried in soft sediments. Tube anemones live inside and can withdraw into tubes, which are composed of a fibrous material made from secreted mucus and threads of nematocyst-like organelles known as ptychocysts. Within the tubes of these ceriantharians, more than one polyp is present, which is an exceptional trait because species that create tube systems usually contain only one polyp per tube.[1] Ceriantharians were formerly classified in the taxon Ceriantipatharia along with the black corals[2] but have since been moved to their own class, Ceriantharia.
Ceriantharians have a crown of tentacles that are composed of two whorls of distinctly different-sized tentacles. The outer whorl consists of large tentacles that extend outwards. These tentacles taper to points and are mostly used in food capture and defense. The smaller inner tentacles are held more erect than the larger lateral tentacles and are used for food manipulation and ingestion.[3] The tentacles of Ceriantharians are also venomous, similar to Cnidarians, which allows them to protect themselves from predators. The recent exploration of Ceriantharians and their venomous tentacles permits the exploration of the lineage of venom genes in Anthozoas. [4]
A few species such as Anactinia pelagica are pelagic and are not attached to the bottom; instead, they have a gas chamber within the pedal disc, allowing them to float upside down near the surface of the water.[5][6]
^Molodtsova, T. (2015). Cerianthidae. In: Fautin, Daphne G. (2011) Hexacorallians of the World. Accessed through: World Register of Marine Species on 2016-02-10
