Styela clava

The stalked sea squirt (Styela clava), also known as the club sea squirt, club tunicate, Asian tunicate, leathery sea squirt or rough sea squirt, is a solitary, hermaphroditic, ascidian tunicate that is native to the Pacific coast of Asia, ranging from the Sea of Okhotsk to Japan, Korea and northeast China. It has been introduced widely around the world such as off Australia, New Zealand, both coasts of North America, and Europe. It is considered invasive outside the native range, as adults lack natural predators, can outcompete native animals, feed on their planktonic larvae, and foul fishing gear and boats. In the most extreme cases, it can reach densities of up to 1,500 per square meter (140 per square foot).

Styela clava is a hardy species that can live at temperatures between −2 and 27 °C (28–81 °F), but only breeds above 15 °C (59 °F). Additionally, adults can survive in both marine and brackish water at salinities down to 10 ppt, although breeding only occurs above 25 ppt.

These sea squirts are characterized by their brown or yellow, rough and wrinkled surface. They typically have a length of 8–12 cm (3.1–4.7 in), but can reach up to 20 cm (7.9 in). They can be found on virtually any hard surface (such as rocks, buoys, pilings and shells of mussels) and occasionally on seaweed. It may have been carried to New England waters from Europe (where it arrived in the early 1950s) in ballast water or ship fouling.

Styela clava is called mideodeok (미더덕) in Korea where it is eaten and part of the local dish agujjim.