Silicoflagellates are planktonic marine chromists that are both photosynthetic and heterotrophic. Their internal silica skeletons are composed of a network of bars, and resemble those of radiolarians but are generally much less complex. Silicoflagellate skeletons usually comprise 1-2% of the siliceous component of marine sediments; they are thus much less abundant than diatoms. However, they are widely distributed throughout the world ocean. This specimen of Dictyocha, shown above right, was recovered from modern deep-sea sediments in the North Pacific.
Living silicoflagellates propel themselves with one long eukaryotic flagellum, or undulipodium. The spines on the skeleton may function in retarding sinking, which is of obvious importance to a photosynthetic organism. Only asexual reproduction is known. Silicoflagellate skeletons may vary considerably within a single species, making it difficult to define species.
Silicoflagellates first appear in the Early Cretaceous and become common in the Late Cretaceous. They were somewhat more diverse in the early Cenozoic than they are today.
See also some silicoflagellates from the Monterey Formation of California.
This silicoflagellate was provided by Dr. Daphne G. Fautin of the University of Kansas.