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Dr Alan Channing

Hot spring environments and ecosystems through time
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Heliozoans in Extremis!
 
The hot springs, run-off streams and geothermally influenced wetlands of Yellowstone are also homes for extremophile protozoans. At present the most complete records of their occurrence are from very acidic environments. My research has revealed the presence of the heterotrophic protozoan Acanthocystis in alkali geothermal wetlands where they occur as subfossils within decaying and partially permineralised plant fragments. As so often occurs in my research this was an unexpected find!

During investigations of the process of plant fossilization with a scanning electron microscope, I began to find associated groups of shield-shaped silica scales and rods with bifurcating tips. The origin of these very beautiful objects were a real mystery to me! They were clearly not part of the plants I was studying and they were not fossilised fungi or bacteria that are responsible for decay of the plants and that are also commonly preserved along with the plant tissues.
 
Eventually a mornings googling (sorry web based research) led me to images of silica scaled protozoans such as chrysophytes and heliozoans - and to the research work of Daniel E Wujek who had published on both groups. There are a limited number of accounts of heliozoa in thermal areas - as in Yellowstone most examples come from acid water bodies few from alkaline waters and none from inside decaying plants.
 
The fossil record of heliozoa is even more scant. A few examples are reported from very young (Pleistocene) lake sediments - though the molecular record suggests a much longer record of their existence. The reason for the lack of a fossil record? Well they are small, a few 10s of microns across, the spine and scale clusters disagregate on the animals death, they thus have a relatively low preservation potential and a low chance of being discovered in older rocks. Maybe fossils of hot spring wetland plants offer a possible taphonomic trap to explore for their fossil record.