Pedicellariae
The pedicellariae are appendages distributed over the whole sea-urchins test: on the ambulacral region, around the primary spines, on the aboral side, and on the oral side. These appendages end in a valved head, usually with three valves that open and close with their own set of muscles.
This is the main feature to distinguish Cidaris cidaris from Stylocidaris affinis (after Tortonese, 1965). C. cidaris have a hook at the tip of the pedicellaria and while S. affinis do not express this characteristic.
For instance, one of the main functions of the pedicellaria is the cleaning and removal of undesired epibionts. These particular appendages are subject to further research.
Cidaris cidaris
Clearly visible hook at the tip of of each valve
Stylocidaris affinis
No hook like structure at the tip of the pedicellaria
They can have different shapes:
Globular
0.97mm length (C. cidaris)
Tridactylous
0.908mm lenght (C. cidaris)
Tryphyllous
0.69mm length (S. affinis)