Code IR999999

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Tardigrades are small animals, rarely and somewhat patchily collected from aquatic habitats but more usually found in the surface film of terrestrial bryophytes or in damp soil. Tardigrades move by sluggish crawling and are known as 'water-bears'.

The body is short and stout, usually with annulations, sometimes with more complex plates and spines. There is usually a single pair of simple eyes. There always are four pairs of stumpy, unjointed legs, terminating in claws, pegs or adhesive disks (sometimes on finger-like projections).

Body length may reach 1.2mm but rarely exceeds 0.5mm. The mouth is terminal or sub-terminal and is flanked by paired stylets. The pharynx is of sucking type, as in some flatworms (Platyhelminthes). The anus is located posteriorly, usually with a single genital duct (females) or paired ducts (males) in a cloaca.

The phylum is divided into three orders and eight families. Some families are wholly marine, others cosmopolitan in freshwater. Two orders and four families may occur in Australian inland waters:

Order Heterotardigrada:

1

Tentacles or 'antennae' on the head; four smooth claws on each leg.

2

Tentacles or 'antennae' on the head; heavily sculptured dorsal plates and either some claws with a spur or else some legs with other than four claws.

Order Eutardigrada:

3

No tentacles or 'antennae'. Four claws on each leg. Legs undivided.

4

No tentacles or 'antennae'. Four claws on each leg. Each leg divided at its base into two parts.