Ciona intestinalis (Linnaeus, 1767)
This species is a simple, solitary ascidian, with a thin outer covering or tunic. Overall shape is cylindrical, similar to a vase. The body measures 4-15 cm in length, and attaches to the substrate at its base. The oral and atrial siphons are positioned close together at the anterior end of the body. Overall, the tunic is smooth and translucent, lacking any pigment flecks. A diagnostic red spot at the end of the sperm duct is visible through the tunic.
In the Northeast Pacific, Ciona intestinalis is most similar to another non-native species found in the region, C. savignyi Herdman, 1882.
Ciona intestinalis has been introduced in the Northeast Pacific, with records ranging from Washington to Mexico. This species also has been collected from other locations around the world, including parts of South Africa, southeast Asia, Australia, New Zealand, Hawaii, and South America. In the Atlantic, the species is cryptogenic, with a geographical range that includes northeast United States, Canada, and Greenland, and stretches across northern Europe, Great Britain, and the Mediterranean. Its native geographical range likely includes northern Europe, but remains unclear (Therriault and Herborg 2008, Zhan et al. 2010).