- Kingdom: Animalia
- Phylum: Chordata
- Subphylum: Tunicata
- Class: Ascidiacea
- Order: Stolidobranchia
- Family: Styelidae
- Scientific name: Botryllus schlosseri
- Norwegian: kolonisekkedyr
These colonial sea squirts form 2-4 mm thick sheets. The zooids (animals) are positioned in star shaped formations. In the center of each star there is a common cloak siphon (opening). Each formation includes between 6 and 12 individuals. The color may vary, but white or pale yellow stars on a brown background is common.
These beautiful formations encrust hard surfaces or algae, from the intertidal zone and down to 40 meters depth.
It is widespread in the Atlantic Ocean, on both hemispheres.