Thursday, July 20, 2017

Corallite type: Axial corallites vs. Radial corallites


A final distinction needs to be made; there are two main types of corallite on branching species.  The radial corallites are located along the length of the branches.  A single axial corallite is found at the branch tip; it may be paler than surrounding tissue and is the site of growth on the branch.  Generally axial corallites are larger than radial corallites, however this is not always the case.  Not all branching corals have axial corallites; it is a diagnostic feature of the genus Acropora (p. 1 of the Coral Finder) and one species of Cyphastrea (p. 1c of the Coral Finder).  You should also be aware that branching colonies start life as an encrusting base before the branches form; the axial corallites can be distinguished even at this stage of colony growth.

Branching corals may have two different types of corallite - axial and radial. Axial corallites form the axis of growth at the tip of the branch and are "differentiated" from the surrounding radials (i.e they look different). The genus Acropora is defined by having axial corallites.

Not all branching corals have axial corallites. Here the genus Anacropora has only radial corallites (i.e. the corallite at the branch tip is not differentiated).