Meiobenthos (meso) - organisms ranging in size from 0.1 to 2 mm. It includes lower crustaceans (ostracodes, herpacticids, etc.), small oligochaetes, fish eggs.

Small aquatic organisms living on the bottom that pass through a sieve with a mesh size of 1 mm and are trapped in a sieve with a mesh size of 32 µm. Meiobenthos animals live in the thickness of loose bottom soil (silt, sand), between its particles. The main representatives of meiobenthos are foraminifera, solitary hydroids, rotifers, free-living nematodes, various small crustaceans (barnacles, harpacticoids, equinae, etc.), small ringworms (polychaetes and oligochaetes), cynorhynchs, gastrotrichs. As a rule, the most abundant animals in marine meiobenthos samples are nematodes (70-100 %), with harpacticoids being the second most abundant.

A distinction is made between eumaeobenthos (organisms measuring 2 mm as adults) and pseudomeiobenthos (organisms up to 2 mm. only in early stages of development).