Actinophrys (Protozoan) Videos

Originally named "Sun Animalcules," these predatory organisms belong to the protozoan class Heliozoa (superclass Actinopoda). They are found most often in freshwater, floating in the open water amongst reeds and filamentous algae. Actinophrys is notable for having more than one nucleus. In general, heliozoans are spherical and are frequently enveloped by a shell, or test, made of silica or organic material. Organisms secrete the shell in the form of scales or pieces in a gelatinous covering. The shells exhibit a wide variety of shapes, which can be used in species identification. Heliozoans reproduce asexually by binary fission or by budding, but several genera have flagellated forms that may possibly be sex gametes.

A unique feature of the superclass Actinopoda is the presence of specialized pseudopodia, called axopodia, that extend outward in a rayed pattern. These appendages are used for locomotion and for capturing food: protozoans, algae, and other small organisms. Axopodia are made of a central core containing a bundle of microtubules, surrounded by an outer layer of flowing cytoplasm. The microtubules are cross-linked in specific patterns that vary from species to another. The outer cytoplasm may contain organelles that can be extruded and used in capturing prey. Although some axopod species can retract their axopodia quickly while others are very slow, most are slow to re-extend them. The manner in which the axopodia move also differs amongst species.