Description: This group encompasses calcareous species that form extensive, thin, pink or purplish crusts (white when dead). Crusts usually range from 1-5 mm (0.04-0.2 in) thick, and their surface can appear smooth, pitted, or have rounded protuberances. Habitat: These perennial crusts are found on rock or shell in the high intertidal (uncommon) to the low intertidal and subtidal (very common) of semi-protected to exposed habitats. Included taxa: Boreolithothamnion, Bossiella, Chamberlainium, Clathromorphum, Leptophytum, Lithophyllum, Mesophyllum.