The crustacean order Tanaidacea (known as tanaids) make up a minor group within the class Malacostraca. There are about 940 species in this order.
Description Tanaids are small, shrimp-like creatures ranging from in adult size, with most species being from . 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. The remaining six thoracic segments each bear a pair of pereiopods, and each of the first five abdominal segments normally carry pleopods. The final segment is fused with the telson and carries a pair of uropods.
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.
Habitat Most are marine, but a handful are also found in freshwater. They live buried in bottom sediments, sometimes in self-built tubes.
Life cycle 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.
Taxonomy The oldest representatives of the group are known from the Carboniferous, with modern forms emerging during the Mesozoic.
The order Tanaidacea is divided into the following sub-orders, superfamilies and families:
Suborder Anthracocaridomorpha † Family Anthracocarididae † Brooks, 1962 emend. Schram, 1979 Family Niveotanaidae † Polz, 2005 Suborder Apseudomorpha Superfamily Apseudoidea Leach, 1814 (incl. former superfamily Jurapseudoidea) Family Apseudellidae Gutu, 1972 Family Apseudidae Leach, 1814 Family Eucryptocaridae Heard et al. 2020 Family Gigantapseudidae Kudinova-Pasternak, 1978 Family Jurapseudidae † Schram, Sieg & Malzahn, 1986 Family Kalliapseudidae Lang, 1956 Family Metapseudidae Lang, 1970 Family Numbakullidae Gutu & Heard, 2002 Family Ophthalmapseudidae Heard et al. 2020 Family Pagurapseudidae Lang, 1970 Family Pagurapseudopsididae Gutu, 2006 Family Parapseudidae Gutu, 1981 Family Protoapseudoidae Heard et al. 2020 Family Sphaeromapseudidae Larsen, 2012 Family Sphyrapodidae Gutu, 1980 Family Tanzanapseudidae Bacescu, 1975 Family Whiteleggiidae Gutu, 1972 Genus Palaeotanais † Reiff, 1936 Superfamily Cretitanaoidea † Schram, Sieg, Malzahn, 1983 Family Cretitanaidae † Schram, Sieg & Malzahn, 1986 Suborder Tanaidomorpha Superfamily Neotanaoidea Sieg, 1980 Family Neotanaidae Lang, 1956 Superfamily Paratanaoidea Lang, 1949 Family Agathotanaidae Lang, 1971 Family Akanthophoreidae Sieg, 1986 Family Alavatanaidae † Vonk & Schram, 2007 Family Anarthruridae Lang, 1971 Family Colletteidae Larsen & Wilson, 2002 Family Cryptocopidae Sieg, 1977 Family Heterotanoididae Bird, 2012 Family Leptocheliidae Lang, 1973 Family Leptognathiidae Sieg, 1976 Family Mirandotanaidae Blazewicz-Paszkowycz & Bamber, 2009 Family Nototanaidae Sieg, 1976 Family Paratanaidae Lang, 1949 Family Pseudotanaidae Sieg, 1976 Family Pseudozeuxidae Sieg, 1982 Family Tanaellidae Larsen & Wilson, 2002 Family Tanaissuidae Bird & Larsen, 2009 Family Tanaopsidae Błażewicz-Paszkowycz & Bamber, 2012 Family Teleotanaidae Bamber, 2008 Family Typhlotanaidae Sieg, 1984 Superfamily Tanaidoidea Nobili, 1906 Family Tanaididae Nobili, 1906
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