Diversity of Protists III

Rhizaria represent a diverse group of protists that possess threadlike pseudopodia. There are three major subgroups — Chlorarachniophyta, Foraminifera, and Radiolaria.

Chlorarachniophyta are phototrophic protists found in both freshwater and marine environments.

They have chloroplasts with four membranes due to algal endosymbionts that were acquired during secondary endosymbiosis.

Foraminiferans are strictly marine protists that build shell-like structures called tests, composed of calcium carbonate and organic material.

Most foraminiferans extend outward from their tests to feed on decaying organic matter, bacteria, or other small protists on the ocean floor.

Some foraminiferans are planktonic and host endosymbiotic algae for nutrients.

Radiolarians are marine planktonic chemoorganotrophs. They possess tests composed of silica.

Radiolarians inhabit the upper 100 m of the ocean, where they remain suspended by lipid droplets, large cytoplasmic vacuoles, and needle-like pseudopodia.

They feed on bacteria and organic matter. In contrast, some other species establish symbiotic, but not endosymbiotic, relationships with algae.