Meiofauna is loosely defined as animals capable of passing through a 0.5-mm mesh. Those associated with various marine sediments include entire phyla (such as kinorhynchs and gastrotrichs), entire major clades of other invertebrate phyla (especially among the arthropods, nematodes, annelids and platyhelminthes), as well as miniaturized representatives of most other animal phyla. Meiofauna probably accounts for well in excess of half the diversity present in complex biotopes such as coral reefs, with most but not all of it associated with sediments. While the great phylum and class level diversity of meiofauna is well-known, the genus and species-level diversity remains largely un-explored and un-documented. Previous, mostly morphological studies of meiofauna have led to groundbreaking insights about evolution, adaptation, and functional biology (e.g., adhesive and sensory structures), as well as fundamental insights into the evolution of the major animal groups in the tree of life.
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