based on either ecological characteristics or biogeochemical effects. While the prevailing categorization is based on the way bioturbators transport and interact with sediments, the various groupings likely stem from the relevance of a categorization mode to a field of study (such as ecology or sediment biogeochemistry) and an attempt to concisely organize the wide variety of bioturbating organisms in classes that describe their function. Examples of categorizations include those based on feeding and motility, feeding and biological interactions, and mobility modes. The most common set of groupings are based on sediment transport and are as follows: Gallery-diffusers create complex tube networks within the upper sediment layers and transport sediment through feeding, burrow construction, and general movement throughout their galleries. Gallery-diffusers are heavily associated with burrowing polychaetes, such as Nereis diversicolor and Marenzellaria spp. Biodiffusers transport sediment particles randomly over short distances as they move through sediments. Animals mostly attributed to this category include bivalves such as clams, and amphipod species, but can also include larger vertebrates, such as bottom-dwelling fish and rays that feed along the sea floor. Biodiffusers can be further divided into two subgroups, which include epifaunal (organisms that live on the surface sediments) biodiffusers and surface biodiffusers. This subgrouping may also include gallery-diffusers, reducing the number of functional groups. Upward-conveyors are oriented head-down in sediments, where they feed at depth and transport sediment through their guts to the sediment surface. Major upward-conveyor groups include burrowing polychaetes like the lugworm, Arenicola marina, and thalassinid shrimps. Downward-conveyor species are oriented with their heads towards the sediment-water interface and defecation occurs at depth. Their activities transport sediment from the surface to deeper sediment layers as they feed. Notable downward-conveyors include those in the peanut worm family, Sipunculidae. Regenerators are categorized by their ability to release sediment to the overlying water column, which is then dispersed as they burrow. After regenerators abandon their burrows, water flow at the sediment surface can push in and collapse the burrow. Examples of regenerator species include fiddler and ghost crabs. Ecological Roles The evaluation of the ecological role of bioturbators has largely been species-specific. However, their ability to transport solutes, such as dissolved oxygen, enhance organic matter decomposition and diagenesis, and alter sediment structure has made them important for the survival and colonization by other macrofaunal and microbial communities. Microbial communities are greatly influenced by bioturbator activities, as increased transport of more energetically favorable oxidants,