Generally hemispherical mass with deeply gouged valleys spearated by steep ridges. However where the top of these ridges normally feature narrow or relatively broader separation lines between opposing septa (like most other brain corals, see Symmetrical Brain Coral or Boulder Brain Coral) they can here feature very wide separation furrows - the grooves - as exemplified by one of the photos shown below, and in particular its red-dotted enlargement. Indeed some specimens can grow unusually wide-angled grooves between separating ridges, but in fact the polyps live in the narrow valleys where their mouths are fed by the many tentacles housed between the septa (the vertical plates).   

Colours, including brown (most common in Western Guadeloupe), green and sometimes grey - depend on zooxanthellae types which, depending on content of particular proteins, can even cause red fluorecence as seen in title photograph - in total absence of special fluo lights.

Zooxanthellae are microscopic photosynthetic algae that live in symbiosis with corals. The latter provide shelter in exchange of which the zooxanthellae supply certain nutriments (including glucose and aminoacids relutling from photosynthesis) that enable them to eventually produce the calcium carbonate used to form their structure.