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 defence. The smaller inner tentacles are held more erect than the larger lateral tentacles and are used for food manipulation and ingestion.[3]
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.[4][5]
^Molodtsova, T. (2015).
Cerianthidae. In: Fautin, Daphne G. (2011) Hexacorallians of the World. Accessed through: World Register of Marine Species on 2016-02-10