Styela clava (Clubbed Tunicate)

Animal Tunicate/Sea-squirt
Family: Styelidae
Classification: Unlisted Invasive Species

Clubbed tunicates (Styela clava) attached to a boat's propeller at Pleasant Harbor in Puget Sound. Photo by Charley Waters

State aquatic managers ask the public to report sightings of tunicates and other aquatic invasive species. To report sightings contact:

Allen Pleus
A quatic nuisance species coordinator for WDFW
(360) 902-2724

Pam Meacham
WDFW Assistant aquatic nuisance species coordinator
(360) 902-2741


A native species to the Pacific coasts of Asia, notably Japan, Korea, and the Philippines, Styela clava is a solitary ascidian (or “sea squirt”) that prefers coastal estuarine and protected marine waters.  It is not considered native to the Pacific Northwest.  Its tough leathery, brownish outer skin (or tunic) shows conspicuous bumps and often wrinkled swellings at the top (posterior) of the body and longitudinal ridges on the bottom (dorsal) part. There are two easily identifiable siphons, an incurrent and an excurrent.  The two siphons usually have longitudinal bands alternating between reddish purple and tan.  S. clava has a gradual to abruptly thin and sometimes flattened lower stalk with variable lengths of up to one-third of the total body length on adults. The younger tunicates, those under one inch in length, do not have a developed stalk. The tunicate attaches directly to a variety of substrates such as rock, wood, shells, but especially preferring artificial structures in protected waters such as pilings, docks, mooring lines, shellfish, aquaculture gear and boat hulls.

S. clava pumps water in through the incurrent siphon, filters out oxygen and feeds on small organisms such as phytoplankton, zooplankton, oyster and mussel larvae, and other suspended organic materials, and then pumps the water as waste out through the excurrent siphon.  The siphons are able to retract when the animal is disturbed.   

Stylela clava, like all sea squirts is hermaphroditic, meaning that it contains both male and female organs.  However the male and female parts of each individual do not mature at the same time, so it does not self fertilize.  Eggs and sperm are broadcast spawned into the water.  The larvae are planktonic for only one to three days before attaching to a hard substrate in spring and summer to metamorphose into a sessile adult.  The Club tunicate can live 2 to 3 years and grow to 6 inches in length. It reaches sexual maturity within 10 months at about 3.5 inches and is capable of reproducing several times during its lifetime.            

See the Tunicate information page for more information

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