The Biology and Ecology of lotic Tardigrada

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1. Tardigrades comprise a micrometazoan phylum that is a sister group of the arthropods. 2. They are components of the meiobenthos in lotic habitats, and ≃ 50-70 species have been reported in such habitats world-wide. Approximately 800 species have been identified from all marine, freshwater, and terrestrial habitats. 3. Taxonomy is based primarily on the morphology of the claws, buccal-pharyngeal apparatus, cuticle and eggs. 4. Reproductive modes include sexual reproduction (amphimixis) and parthenogenesis. The sexual condition of individuals may be either gonochorism, unisexuality, or hermaphroditism. Moulting occurs throughout the life of the tardigrade. 5. Latent states (cryptobiosis, including encystment, anoxybiosis, cryobiosis, osmobiosis and anhydrobiosis) enable tardigrades to withstand unfavourable environmental conditions. 6. Population densities, life histories, dissemination and biogeography of freshwater species are poorly known.