Image Information: This image nearly crashed my computer – it is a stack of 27 separate images to increase the depth of field. The computer worked nearly an hour on this picture. Without stacking, some of the tentacles would not be in focus. I think that less pictures would have given a similar result. The picture on the right shows the fresh-water polyp Hydra sp. The specimen is about 5mm in length, the picture shows about half of the organism.


Background Information: The Hydra belongs to the taxon Cnidaria and is a relative of the sea anemones, corals and jelly fish. Its tentacles are used to catch food. It is sessile, this means that it is attached to a solid surface and does not move. The mouth of the hydra is located towards the left of the image, where the tentacles attach to the body.