Description: Thin sheet forming extensive patches on rock surfaces. In encrusting form it can be easily detached from the substrate. The literature claims "Can become branched - erect, sometimes stalked", but BEP considers this to refer to a separate species. Watery orange to bright red. Fairly tough sheet, which holds together well when scraped off. Oscules conspicuous, spaced regularly across the surface, with slightly raised conical rims; circular and consistent in size. Ostia apparent on close examination. Excurrent channels are inconspicuous, not at the surface of the colony, but their ends are visible inside the oscules.

Habitat: Vertical or steeply inclined rock faces in both sheltered and exposed places.

Distribution: "South coast of England; France; Spain; Mediterranean etc." Known recently from Skomer; Rathlin Island. Confusion with Antho inconstans (q.v.) leaves previous records in doubt.

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

iNaturalist: Antho involvens at iNaturalist World Species Observations database.