Nassellaria

Nassellaria, the third of the four orders into which Haeckel has divided the class Radiolaria (q.v.). The characteristics of the order are the siliceous skeleton and the fact that the pores in this are limited to a pore area (or porochora) at one end of the main axis of the body. The order includes many familiar forms, e.g. the helmet-shaped Cystoidea.