Cruoria is a genus of crustose red alga – that is, a seaweed.
It resembles the genera Ralfsia, Lithoderma and Hildenbrandtia.[herba.msu.ru/hyperkey/ws-algae/g2/hildenbr.htm]
References
External links http://www.algaebase.org/search/species/detail/?species_id=117 : Algaebase. Contains images.