Description: Colonies are usually thick crusts, divided into lobes. There are two colour forms, a white one and a pink one, this colour emanating from the test. The zooids are rather irregularly arranged around a series of large conspicuous cloacal openings in the upper surface of the colony. The six lobes of the oral siphon are heavily pigmented in white, as is the large atrial languet. The upper part of the branchial basket and endostyle are pigmented with white to a variable degree. 5mm thick x 20-50mm across.

Habitat: A typical surge-gully, upper infralittoral exposed water species. Usually on rock surfaces, also in more sheltered situations on vertical rock faces.

Ecology: Probably overwintering in a dormant form like most other polyclinids.

Distribution: Western coasts from Scotland to Cornwall and south to the Mediterranean. East coast records would be interesting.

Similar Species: The most distinctive, conspicuous and easily recognised polyclinid. Most likely to be confused with Botryllus schlosseri or Botrylloides leachii, or with Sidnyum elegans. Aplidium proliferum is considered to be a distinct species by some authors. If it is a distinct entity then it looks very like Sidnyum elegans but has only 6 papillae around the oral siphon.

Key Identification Features:

• Flat-topped broad-based colonies.
• White pigmentation of oral lobes and atrial languet.
• Large conspicuous cloacal openings.

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

iNaturalist: Aplidium nordmanni at iNaturalist World Species Observations database.

WoRMS: Aplidium nordmanni at World Register of Marine Species. Accepted name: Aplidium nordmanni (Milne Edwards, 1841). AphiaID: 103656.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Aplousobranchia; Polyclinidae; Aplidium