noun
radiolarian
A type of marine plankton with intricate mineral skeletons; used in biology and earth science.
放散虫の化石は、地層の年代を決めるのに役立つ。
Radiolarian fossils are useful for determining the age of geological strata.
Compound of 放散 (hōsan, 'diffusion, scattering') and 虫 (chū, 'insect, worm, bug'), referring to the radiating pseudopodia of these organisms. The exact historical derivation is uncertain.