Little is known about coralligenous habitats. Besides acknowledging them as a typical Mediterranean marine habitat, biologists hardly agree on a common definition. Coralligenous habitats are characterized by encrusting calcareous algae and contain more than 1,500 identified species. Particularly beautiful, they can display red coral, gorgonians, bryozoans, and sponges. The species, shapes, and colors of these habitats differ from one region to another and, in particular, between the East and West and the North and South of the Mediterranean. Though they've been studied very little, they nevertheless are one of the Mediterranean’s richest habitats in terms of species, along with seagrass Posidonia oceanica (marine plants found close to the surface) and deep-sea coral (studied little due to it being inaccessible).