Final answer:
Radiolarians are a subgroup of Rhizaria known for their silica-based intricate skeletons, which function in food capture and contribute to ocean sediment layers and the fossil record.
Step-by-step explanation:
Radiolarians are a subgroup of Rhizaria, which is a major group of mostly unicellular eukaryotes. They possess intricate exteriors composed of glassy silica and can exhibit either radial or bilateral symmetry. Their pseudopods, which radiate outward from the cell bodies, are supported by microtubules and function in capturing food particles. Radiolarians are notable in that their shells, made of silica, sink to the ocean floor upon death and can accumulate in thick layers, making them a significant part of the fossil record. A notable feature of radiolarians is their fossilized shells, which can be imaged using scanning electron microscopes to reveal detailed structures as depicted in Figure 23.19.