Three-dimensional visualisation of brooding behaviour in two distantly related brittle stars from South African waters

In South African waters, brooding occurs both in the very small amphiurid Amphipholis squamata , which is hermaphroditic, and in the large ophiodermatid Ophioderma wahlbergii , which is gonochoric. For the first time, microcomputed tomography was applied to visualise and compare brooding and brooded young of these two brittle star species from two distantly related families.

The scanned A. squamata brooded six young, whereas O. wahlbergii brooded 13 young. Volume measurements of the adults revealed that A. squamata dedicated about 25% of its disc volume to brooding and O. wahlbergii about 14%. Although the brooded young of O. wahlbergii are thought to be among the largest of all known ophiuroids, young of A. squamata were four times larger in relation to adult body disc volume.