Pedinellales

Pedinellales is a group of heterokonts.

These are found in both freshwater and marine environments, and most genera are sessile, attached by posterior stalks. The flagellum is at the anterior of the cell, and the tentacles surround it, often capturing small prey drawn in by its current. The colored genera are Pedinella, Apedinella, Pseudopedinella, and Mesopedinella. Several more genera have lost their chloroplasts and feed entirely by phagocytosis. These are Parapedinella, Actinomonas, and Pteridomonas.

It also appears that certain heliozoa are actually derived pedinellids. Ciliophrys alternates between a mobile flagellate stage and a heliozoan feeding stage, where the body is contracted with extended axopods all over its surface, and the flagellum is curled up into a tight figure eight. The actinophryids, Actinophrys and Actinosphaerium, exist only in a heliozoan form with no flagellum and with more elaborate bundles of microtubules supporting their axopods. Their inclusion was argued by Mikrjukov and Patterson, who coined the term actinodine to refer specifically to this extended group.

The colored pedinellids were originally treated as a family of golden algae in the order Ochromonadales, promoted to an order Pedinellales by Zimmerman in 1984. Their relationship to the silicoflagellates became apparent some time later, and Patterson defined this rankless group for the two in 1994. Moestrup treated it as the class Dictyochophyceae, previously restricted to the silicoflagellates, while Cavalier-Smith defined a new class Actinochrysophyceae for them.

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