Abstract The term meiobenthos refers to a group of invertebrate organisms that are intermediate in size between macro- and microfauna, and inhabit all sediment types in all marine environments and in all climatic zones. They may occur at enormously high densities of millions of individuals per square metre; this means that 10 cm 3 of sediment in any given habitat may contain thousands of these organisms. Although meiobenthos in some extreme arctic habitats is uncommonly poor, the abundance and composition of the polar or subpolar meiobenthic assemblages are not essentially different from those found in boreal–tropical locations at corresponding sediments and depths.