Didemnum vexillum
| Didemnum vexillum | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Tunicata |
| Class: | Ascidiacea |
| Order: | Aplousobranchia |
| Family: | Didemnidae |
| Genus: | Didemnum |
| Species: | D. vexillum |
| Binomial name | |
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Didemnum vexillum Kott, 2002 |
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| Synonyms | |
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Didemnum vexillum, the carpet sea squirt, is a species of colonial tunicate in the family Didemnidae. Believed to be native to the waters around Japan, it has been reported as an invasive species in a number of places in Europe, North America and New Zealand. It is sometimes given the nickname "D. vex" because of the vexing way in which it dominates marine ecosystems when introduced into new locations.
This bottom-colonizing tunicate can build over most substrates, including cobble, and grows over other organisms when it needs more room to expand. Its appearance has given rise to the common name marine vomit. It was first described from New Zealand as Didemnum vexillum in 2002 by Kott. At the time, he thought he was describing a species new to science.
A colony of Didemnum vexillum consists of a number of sac-shaped zooids connected by a common tunic. Each zooid is about 1 mm (0.04 in) long and has a buccal siphon through which water is drawn into the interior. The water then passes into a shared cavity from which it is pumped out through an atrial siphon. The surface of the colony is smooth, leathery, and often veined in appearance; the buccal siphons appear as numerous fine pores, and the atrial siphons as a smaller number of larger holes. The colony is firmly attached to a hard surface from which it can be difficult to detach.
D. vexillum has different forms in different locations. It can form a thin or thick encrusting mat, or form large or small lobes. The colour can be orange, pink, tan, creamy yellow or greyish-white and the tunic is sparsely strengthened by stellate spicules with nine to eleven rays. Where there is little water movement, the colonies may dangle in ropey masses from hard substrates, such as cables, docks, and the hulls of vessels. In places with stronger currents, they cover the surface of rocks, boulders, pebbles, gravel, and oysterbeds in a thin, encrusting layer.
Didemnum vexillum appears to be native to Japan, where it was recorded in Mutsu Bay in 1926. It is still common there and, as well as growing on rock surfaces and seagrasses (Zostera), it grows as a fouling organism on cultured bivalves, net cages, pilings and other man-made structures. Its depth range is from the intertidal zone down to a depth of about 80 m (262 ft).
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Wikipedia