A tunicate is an exclusively marine invertebrate animal, a member of the subphylum Tunicata. This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still sometimes used for these animals. They are the only chordates that have lost their myomeric segmentation, with the possible exception of the seriation of the gill slits. However, doliolids still display segmentation of the muscle bands.
Ascidiacea, commonly known as the ascidians or sea squirts, is a paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of a polysaccharide.
Ciona intestinalis is an ascidian, a tunicate with very soft tunic. Its Latin name literally means "pillar of intestines", referring to the fact that its body is a soft, translucent column-like structure, resembling a mass of intestines sprouting from a rock. It is a globally distributed cosmopolitan species. Since Linnaeus described the species, Ciona intestinalis has been used as a model invertebrate chordate in developmental biology and genomics. Studies conducted between 2005 and 2010 have shown that there are at least two, possibly four, sister species. More recently it has been shown that one of these species has already been described as Ciona robusta. By anthropogenic means, the species has invaded various parts of the world and is known as an invasive species.
Molgula, or sea grapes, are very common, globular, individual marine tunicates roughly the size of grapes.
Corella willmeriana is a solitary tunicate in the family Corellidae. It is native to the eastern Pacific Ocean where it lives on the seabed at depths down to about 75 m (250 ft) between Alaska and California.
Clavelina picta, common name the painted tunicate, is a species of tunicate, in the genus Clavelina. These animals, like all ascidians, are sessile filter feeders.
Didemnum molle is a species of colonial tunicate in the family Didemnidae. It is commonly known as the tall urn ascidian, the green barrel sea squirt or the green reef sea-squirt. It is native to the Red Sea and the tropical waters of the Indo-Pacific region.
Ciona savignyi is a marine animal sometimes known as the Pacific transparent sea squirt or solitary sea squirt. It is a species of tunicates in the family Cionidae. It is found in shallow waters around Japan and has spread to the west coast of North America where it is regarded as an invasive species.
Ascidia mentula is a species of solitary tunicate. It is found in the north east Atlantic Ocean, the Mediterranean Sea and Black Sea. It occurs round the coasts of Britain but is seldom seen on the east coast of England or Scotland.
Molgula oculata, commonly known as the sea grape, is a species of solitary tunicate in the family Molgulidae. It is native to the north eastern Atlantic Ocean and the North Sea. The specific name oculata means "having eyes"; the species has orifices which "seem like dark eyes within a spectacle-formed frame".
Okenia leachii is a species of sea slug, a Dorid nudibranch, a marine gastropod mollusc in the family Goniodorididae.
Polycarpa fibrosa is a species of tunicate in the family Styelidae. It is brown and globular and its outer surface is covered with a mat of fibrils. It normally lies buried in soft sediment on the seabed with only its two siphons protruding. It occurs in the Arctic Ocean and northern Atlantic Ocean. P. fibrosa was first identified and described by the American malacologist William Stimpson in 1852.
Molgula citrina is a species of solitary tunicate in the family Molgulidae. It is found on both sides of the northern Atlantic Ocean and in the Arctic Ocean. In 2008 it was found in Kachemak Bay in Alaska, the first time it had been detected in the Pacific Ocean.
Polycarpa pomaria is a species of tunicate or sea squirt in the family Styelidae. It is native to the northeastern Atlantic Ocean where it lives on the seabed at depths down to about 450 metres (1,500 ft).
Phallusia mammillata is a solitary marine tunicate of the ascidian class found in the eastern Atlantic Ocean and the Mediterranean Sea.
Molgula occidentalis is a species of marine invertebrate of the family Molgulidae. The scientific name of the species was validated and published for the first time in 1883 by Traustedt. It is a soft-bodied, intertidal ascidian, sac-like filter feeders in the subphylum tunicate characterized by a hard outer covering known as a “tunic,” abundant in the shallow subtidal and intertidal zones of the Northern Gulf of Mexico, where they establish pseudopopulations.
Boltenia villosa is a species of tunicate, a marine invertebrate of the family Pyuridae. Common names include spiny-headed tunicate, hairy sea squirt, stalked hairy sea squirt and bristly tunicate. This species was first described in 1864 by the American marine biologist William Stimpson who gave it the name Cynthia villosa. It was later transferred to the genus Boltenia. The type locality is Puget Sound, Washington state, United States.
Pyura haustor is a species of sessile ascidian, or sea squirt, that lives in coastal waters in the north-eastern Pacific Ocean, attached to rocks or artificial structures. Common names for this species include the wrinkled seapump, the wrinkled sea squirt and the warty tunicate.
Tunicotheres is a monotypic genus of crabs in the family Pinnotheridae, and Tunicotheres moseri is the only species in the genus. This crab lives commensally in the atrial chamber of a small ascidian. It is found in the tropical western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico.
Clavelina ossipandae, the skeleton panda sea squirt or skeleton panda ascidian, is a species of colonial ascidian, a group of sessile, marine filter-feeding invertebrates. Originally discovered near Kume Island in Japan by local divers, pictures of the animal attracted attention in the media for its appearance prior to its formal taxonomic description in 2024.
