放ほう散さん虫ちゅう

noun

radiolarian

A type of marine plankton with intricate mineral skeletons; used in biology and earth science.

• 放ほう散さん虫ちゅうの化か石せきは、地ち層そうの年ねん代だいを決きめるのに役やく立だつ。

  Radiolarian fossils are useful for determining the age of geological strata.