Centrohelida and other heliozoan-like protists

Abstract

The Centrohelida has arisen through the dissolution of the Heliozoa and the gradual removal of morphologically similar, but ultrastructurally and genetically distinct taxa from the group. The taxonomy of these other heliozoan-like protists is still largely in flux, as are the groups within the Centrohelida. Centrohelida and heliozoan-like protists are heterotrophic, free-living species that are found in most aquatic benthic environments where they feed on bacteria and other protists, including algae. Morphologically the cells are conspicuous, generally round in shape with eye-catching raylike axopodia. They can be found in habitats that represent a wide range of temperatures and salinities, including extreme environ- ments. Most are free floating, but some attach to substrates by a stalk. Interest in the heliozoan-like protists ("sun animalcules") is largely in regard to cell biology. Their size (some can be 500 pm in diameter) and axopodial structure have made them useful subjects for biochemical and ultrastructural studies of microtubules.