Description: Thin sheets covering extensive areas, typically 3mm thick by up to 30cm diameter. In the literature it has been reported as a cushion, but this may be the result of the sponge growing over a saddle oyster (BEP). Typically looks like a patch of red paint. Bright red, scarlet or blood red. The blood-red sublittoral form is described here, and may be a distinct species from the scarlet one which seems to occur both in the littoral and sublittoral. Difficult to determine because of thinness of sheet but fairly soft; difficult to scrape off - it crumbles and tears. Oscules have slightly raised transparent rims, apparent mainly because of converging excurrent channels. These oscules are "numerous and regularly spaced over the surface".

Habitat: Vertical surfaces of rock or wrecks. Boulders in brackish conditions. Encrusting pebbles in areas of strong current (Menai Straits) in the Littoral zone.

Distribution: "Atlantic coasts of Europe (from Shetlands southwards), Mediterranean etc." Known recently from Strangford Lough; Rathlin Island; Menai Straits; Daucleddau, Milford Haven. Littoral or shallow sublittoral.

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

iNaturalist: Microciona atrasanguinea at iNaturalist World Species Observations database.