Protozoa with amoeba-like bodies and radiating filamentous pseudopods

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Radiolarian \Ra`di*o*la"ri*an\ (r[=a]`d[i^]*[-o]*l[=a]"r[i^]*an), a. (Zo["o]l.) Of or pertaining to the Radiolaria. -- n. One of the Radiolaria.

Wiktionary Word definitions in Wiktionary
n. Any of many marine amoeboid protozoa, of subclass Radiolaria, having filamentous pseudopodia; they have intricate silica skeletons

WordNet Word definitions in WordNet
n. protozoa with amoeba-like bodies and radiating filamentous pseudopods

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1862, from Radiolaria , Modern Latin classification name, from Latin radiolus , diminutive of radius (q.v.).