Introduction to some aquatic protozoa in Essex
Figures 6a and b. Beating cilia of Stentor polymorphus © Steve Durr
Heliozoans
Another interesting group of organisms that can be readily found in most ponds are the heliozoans.
These animals are spherical in nature and have axopodia, which radiate out in all directions and look
like miniature suns. They are commonly known as sun animalcules and they were first observed
hundreds of years ago. The two most common forms of this type of animal that you will see are
Actinophrys sol and Actinosphaerium both of which can be readily found if a pond net is employed.
The photograph below in Figure 7 was taken on a x40 DIC objective and shows the Heliozoan
Actinosphaerium. which is large enough to be seen with the naked eye. The axopodia arc used for
catching prey and also as a means of moving around.
Figure 7. The heliozoan Actinosphaerium showing its radiating axopodia © Steve Durr
Essex Naturalist (New Series) 18 (2001)
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