 |
Photograph of a Heliozoan taken with a X40 Nomarski objective. The large round object in the middle is the nucleus, while the outer part of the cell body are covered with large vacuoles.These protozoa can be found floating around filamentous algae and larger water plants. |
These microbes are found floating in the open water between reeds and the filamentous algae. With some 34 genera and nearly 100 species this is a very successful phylum. They are spherical in design with long filaments, which are primarily used for snaring prey, but can be used for movement. One of the commonest of all species of the heliozoa is actinophrys sol or the sun animalcule. Actinophrys can often be found lurking between the filaments of algae waiting to come into contact with some protozoan or motile algae. The specimens that I have collected have all come from a small pond in Epping Forest called Wake valley pond. I usually collect them from a set of reed beds to the north of the pond, with the best time being early spring through to summer. This year the pond was still yielding large amounts of this protozoan up until October. When searching for this microbe it is best to use a low power phase objective e.g. X10- X16. The average size of actinophrys is about 50um across the cell body. The cell nucleus can be difficult to see but is discernible easily with differential interference contrast and measures about 12um in diameter. The most distinguishing feature about this microbe is the long stiff radiating spines that give this animal its name.
 |
This photograph was taken with bright field optics at a magnification of X250. The bar at the base of the photograph represents 50um in length. The axopodia can be anything from 50um - 150um in length, and have what are called extrusomes that migrate along the axopodia. Extrusomes are sticky pads that attach to the prey preventing its escape. |
The axopodia are fine projections that are used for the capture of prey and also to a lesser degree for moving the animal around. It can be seen from Fig # 1 that the axopodia are of all different lengths and are all stiffened by a microtuble axoneme. Heliozoans feed by engulfing their prey by a method called phagocytosis, which is common to this type of animal. Many amoebas and (white blood cells found within the human body) also use this method of feeding. They will devour anything that comes within range and the size of the prey does not seem to deter them, a most fascinating animal to observe.
Actinophrys reproduce by a method called binary fission but they can also reproduce by autogamy, which is useful when a population needs to be established quickly.
 |
This photograph shows the extreme frothy nature of the outer cell body. Two large food vacuoles are also present with the remains of its last meal still visible. When large amounts of vacuoles appear like this it is a sure sign that the microbe is feeding very well. |
A few years ago I observed what appeared to be two actinophrys sharing a meal. They separated shortly afterwards with one protozoan taking off with the meal. A set of photographs were taken of this event.
 |
 |
 |
 |
 |
|
 |
This specimen, also from Epping forest, is also very common among the water weeds and is called Acanthocystist. Looking carefully at the axopodia, many of the extrusomes that the microbe uses to catch its prey with can be seen.This specimen was photographed with T-Max 100 using a X50 Leitz water immersion lens. |
One of my favourite heliozoans is the very large Actinosphaerium which can grow up to a width of 1mm. The largest specimen that I have recorded in the Wake valley pond was 280um in diameter. Spotting this large heliozoan is easy and once seen, never forgotten.
 |
 |
 |
 |
|
This Heliozoan was found in a sample of water from Wake valley pond and photographed with a X40 phase contrast objective. Again it is very difficult to put a name to this species. |