INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOA

SARCODINES

PHYLUM AMOEBOZOA

RADIOLARIANS

CLASS PHAEODAREA

Specialized deep-Water radiolarians possessing a monolithic silica-organic Skeleton of diverse shapes, supplemented by radial needles. A peripheral multi-layered zone of needles is frequently present. Instead of numerous pores, the central capsule features three openings: one Functions as a cytostome, while the other two serve for The Emergence of axopodia. Phaeodarians differ from representatives of other classes by the presence of a distinctive brown Structure known as the phaeodium. This is an accumulation of indigestible food remains and symbionts involved in silicon METABOLISM. Representative species of the Class include Castanidium variabile and Challengeron (Fig. 25, c, d).

Radiolarian skeletons settle to the ocean floor, forming deposits of sedimentary rocks known as radiolarites, which have industrial Applications such as siliceous clays, shales, tripoli, as well as semi-precious stones like jasper, opal, and chalcedony. The island of Barbados in the Caribbean Sea is composed primarily of tripoli. Radiolarians are known to have existed since the Cambrian period. Along with foraminifers, they serve as index fossils in stratigraphy (the branch of geology concerned with the sequence and spatial distribution of sedimentary rock strata, their geological age, and mutual relationships).