Species description: Although this is a solitary sea squirt it often forms clumps, with each individual reaching up to 4 cm in length. They are orange-red in colour with an oval-shaped, bulbous body, and are generally attached by a broad base. There are two fluted siphons with conspicuous white to cream markings on the inside which resemble the points of a compass. The stripes on the siphons can still be seen even when the siphons are partly closed. The siphons and the surface of the body may have several small warts.

Habitat: Found in and around harbours, marinas and aquaculture sites, where it fouls ships' hulls, pontoons and buoys.

Distribution: First reported in Northern Ireland in 2018 from Strangford Lough, and is now present at various marinas and harbours all around NI. Records from south of England and a few scattered records from Wales. So far no records from northern England or Scotland, aside from some occurrences in Orkney.

Similar Species: Compass markings on the inside of the siphons are diagnostic. Could potentially be confused with native species Pyura microcosmus, although it is dirty-brown in colour.

Key Identification Features:

• Overall orange-red colouration.
• Compass-like marks on siphons.
• Small warts on outer parts of siphons and body.

Distribution Map from NBN: Asterocarpa humilis at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Asterocarpa humilis at iNaturalist World Species Observations database.

WoRMS: Asterocarpa humilis at World Register of Marine Species. Accepted name: Asterocarpa humilis (Heller, 1878). AphiaID: 250047.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Stolidobranchia; Styelidae; Asterocarpa