Tube-dwelling anemones or ceriantharians look very similar to

sea anemone Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...

s but belong to an entirely different

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

anthozoa Anthozoa is a subphylum of marine invertebrates which includes the sea anemones, stony corals and soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plankton. The basic unit of ...

ns. 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 A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

-like

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

s 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. Ceriantharians were formerly classified in the taxon Ceriantipatharia along with the black corals but have since been moved to their own subclass, 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. A few species such as '' Anactinia pelagica'' are

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

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.

Taxonomy

;Order Spirularia * Family Botrucnidiferidae Carlgren, 1912 ** Genus '' Angianthula'' Leloup, 1964 ** Genus '' Atractanthula'' Leloup, 1964 ** Genus '' Botruanthus'' McMurrich, 1910 ** Genus '' Botrucnidiata'' Leloup, 1932 ** Genus '' Botrucnidifer'' Carlgren, 1912 ** Genus '' Calpanthula'' van Beneden, 1897 ** Genus '' Cerianthula'' Beneden, 1898 ** Genus '' Gymnanthula'' Leloup, 1964 ** Genus '' Hensenanthula'' van Beneden, 1897 ** Genus '' Ovanthula'' van Beneden, 1897 ** Genus '' Sphaeranthula'' Leloup, 1955 * Family Cerianthidae Milne-Edwards & Haime, 1852 ** Genus '' Anthoactis'' Leloup, 1932 ** Genus '' Apiactis'' van Beneden, 1897 ** Genus '' Bursanthus'' Leloup, 1968 ** Genus '' Ceriantheomorphe'' Carlgren, 1931 ** Genus '' Ceriantheopsis'' Carlgren, 1912 ** Genus ''

Cerianthus ''Cerianthus'' is a genus of tube-dwelling anemones in the Family (biology), family Cerianthidae. Members of the genus are found worldwide. They are Predation, predators, scavengers and omnivores. Characteristics Members of this genus do not hav ...

'' Delle Chiaje, 1830 ** Genus '' Engodactylactis'' Leloup, 1942 ** Genus '' Isodactylactis'' Carlgren, 1924 ** Genus '' Nautanthus'' Leloup, 1964 ** Genus '' Pachycerianthus'' Roule, 1904 ** Genus '' Paradactylactis'' Carlgren, 1924 ** Genus '' Parovactis'' Leloup, 1964 ** Genus '' Peponactis'' van Beneden, 1897 ** Genus '' Plesiodactylactis'' Leloup, 1942 ** Genus '' Sacculactis'' Leloup, 1964 ** Genus '' Solasteractis'' van Beneden, 1897 ** Genus '' Synarachnactis'' Carlgren, 1924 ** Genus '' Syndactylactis'' Carlgren, 1924 ** Genus '' Trichactis'' Leloup, 1964 ;Order Penicillaria * Family Arachnactidae McMurrich, 1910 ** Genus '' Anactinia'' Annandale, 1909 ** Genus '' Arachnactis'' Sars, 1846 ** Genus '' Arachnanthus'' Carlgren, 1912 ** Genus '' Dactylactis'' van Beneden, 1897 ** Genus '' Isapiactis'' Carlgren, 1924 ** Genus '' Isarachnactis'' Carlgren, 1924 ** Genus '' Isarachnanthus'' Carlgren, 1924 ** Genus '' Isovactis'' ** Genus '' Ovactis'' ** Genus '' Paranactinia'' A 2020 integrative study incorporating

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

reconstructions and morphological assessment across the three families recovered Arachnactidae as a well-supported

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

, but did not recover Cerianthidae and Botrucnidiferidae as

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

, drawing into question the validity of the Spirularia suborder

References

External links

Photos of Tube Anemones

Tube-dwelling anemone toxins have pharmacological potential, mapping study shows
on: Eurekalert!, 29 October 2020. Source: Fundação de Amparo à Pesquisa do Estado de São Paulo {{Taxonbar, from=Q245695 Anthozoa Animal classes