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Introduction to Tardigrades.
Tardigrade Gallery.

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Textbook Tardigrades.

  The Tardigrada (Water Bears).

"Tardigrades might have been specially designed for the delight and convenience of microscopists. They can be found almost anywhere, can be stored dry until required -- just adding water will revive them -- and they are without doubt the most engaging characters of the microscopic world."
Fitter and Manuel: Freshwater Life, Collins, 1986. P. 195.
Named water bears by the early microscopists, most tardigrades are about half a millimetre or less in length, although the larger species can reach a millimetre or so. They are unable to swim. Their cylindrical bodies have four pairs of short legs, each equipped with hooked claws.

Tardigrade means literally "slow stepper", which is not altogether accurate. They are usually in a state of vigourous activity, not always resulting in much forward motion between the glass surfaces of microscope slide and coverglass, but in their normal habitats where their claws find surfaces to thrust against, their progress can be forceful and rapid.
The shapes of the claws are important in the identification of species.

The internal organs are less easy to distinguish than those of rotifers, especially in mature individuals, but the head usually has a pair of small eyespots, and the muscular bulb of the pharynx can normally be seen. The mouth is a complex arrangement consisting of a sucking tube with a circular external part, and a pair of stylets which can be projected from the mouth orifice to penetrate the walls of the plant cells which are the food of the tardigrade.

Click for a diagram of a common tardigrade.

A Tardigrade. A tardigrade obtained by allowing dried moss to soak in water for an hour or two. They can, rather like rotifers, survive for long periods in a totally dried state.

This is a necessary adaptation to a life lived in the film of water which covers the leaves of wet moss -- a common habitat for both tardigrades and rotifers, and one prone to periods of dessication.

The oesophagus and the muscular pharynx can be clearly seen.
Darkfield, x400.
A Tardigrade. Another tardigrade from the same sample as the specimen above. The structural parts of the mouth can be seen more clearly in this picture, but not the pharynx.
Rheinberg, x400.

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