The
dimorphids are a small group of
flagellate heliozoa. There are two genera:
Dimorpha, a tiny organism found in freshwater, and the larger
Tetradimorpha, which is distinguished by having four rather than two flagella. Bundles of
microtubules, typically in square array, arise from a body near the flagellar bases and support the numerous axopods which project from the cell surface. Each cell has a single
nucleus, and
mitochondria with tubular cristae.