Published online by Cambridge University Press: 17 July 2017
Radiolarians are marine zooplankton possessing a tough, central capsular membrane that divides the cytoplasm into intracapsular (containing the nucleus, organelles, and food reserves) and extracapsular (with food-gathering rhizopodia and digestive vacuoles) portions (Figure 1). They bear two kinds of pseudopodia, the axopodia and filopodia. The axopodia extend radially through the ectoplasm and capsular membrane to the interior of the endoplasm. The axopodia are inserted into a special structure, the axoplast (Figure 1). The development of the axoplast and its complex is of fundamental importance in radiolarian taxonomy. For a detailed description of radiolarian cytology, biology, and reproduction, see Anderson (1983).