Botrylloides violaceus is a colonial tunicate of the genus Botrylloides. Its native range is in the Northwest Pacific from Southern China to Japan and Siberia. Colonies attach and grow on solid surfaces and substrates, and consist of individuals arranged in twisting rows. Outside its native range, it is considered an invasive species and are becoming more common in coastal waters of North America and other waters around the world, likely being spread by shipping industries.
In the San Francisco Bay area, B. violaceus can be readily found on boat docks in the Richmond Marina. The ecological impact of B. viollaceus in this region remains unknown.
Zooids are embedded in a transparent tunic and are all connected to one another by a network of blood vessels that terminate in ampullae (small sac-like structures) at the periphery of the colony. Their color varies from bright orange to reddish or dull purple. These tunicates usually have 8 branchial tentacles and 11 rows of stigmata.