Botryllus schlosseri, commonly known as the star ascidian or golden star tunicate, is an invasive, colonial ascidian tunicate that grows on slow-moving, submerged objects, plants, and animals in nearshore saltwater environments.
Individual zooids may grow to 3 millimetres (0.12 in) in size, with colonies reaching 50 millimetres (2.0 in) long.
Its range has spread over the last 100 years to a nearly worldwide extent. Ranging in the western Atlantic Ocean from the Bay of Fundy to North Carolina.
B. schlosseri zooids emanate from a center in the manner of the arms of a star. Also, there usually are fewer zooids per cluster (5–8 in B. schlosseri). The are many colors in which this species can be found, ranging from orange, blue and grey. A colony can be easily be separated from the main body to form an independent colony usually referred to as a subclone. Two colonies may also fuse together if they share a common allele for fusibility histocompactibility.
When sexually productive, these Botryllus are known to produce,"yellowish-white or pale orange tadpole larva" exhibiting an oval outline.
In a study conducted by Heather Boyd, from Stanford University, it was concluded by comparing morphological and genetic experiments that "Botryllus from the Monterey and from Woods Hole, Massachusetts, may be designated contingently as Botryllus schlosseri."