| Tanaidacea Temporal range:
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|---|---|
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| Tanaissus lilljeborgi (a tanaid from the North Sea) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Superorder: | Peracarida |
| Order: | Tanaidacea Dana, 1849 |
| Suborders | |
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The crustacean order Tanaidacea (known as tanaids) make up a minor group within the class Malacostraca. There are about 940 species in this order.
Tanaids are small, shrimp-like creatures ranging from 0.5 to 120 millimetres (0.020 to 4.7 in) in adult size, with most species being from 2 to 5 millimetres (0.08 to 0.2 in). Their carapace covers the first two segments of the thorax. There are three pairs of limbs on the thorax; a small pair of maxillipeds, a pair of large clawed gnathopods, and a pair of pereiopods adapted for burrowing into the mud. Unusually among crustaceans, the remaining six thoracic segments have no limbs at all, but each of the first five abdominal segments normally carry pleopods. The final segment is fused with the telson and carries a pair of uropods.[1]
The gills lie on the inner surface of the carapace. The thoracic limbs wash water towards the mouth, filtering out small particles of food with the mouthparts or maxillipeds. Some species actively hunt prey, either as their only food source, or in combination with filter feeding.[1]
Most are marine, but a handful are also found in freshwater. They live buried in bottom sediments, sometimes in self-built tubes.[2]
Tanaids do not undergo a true planktonic stage. The early developmental period is spent while young are within the marsupium of the mother. Subsequently, post-larvae, called mancas, emerge as epibenthic forms. Some species are hermaphroditic.[1]
The oldest representatives of the group are known from the Carboniferous, with modern forms emerging during the Mesozoic.[2]
The order Tanaidacea is divided into the following sub-orders, superfamilies and families:[3]
