Micromitra was a lampshell with a bivalve (two-part) phosphate shell enclosing most of its body. Between the shells extended a row of thin bristles, protecting Micromitra’s fragile interior from waste products and parasites.

It often lived a sedentary life, attached by its pedicle (foot) among the spines of the sponge Pirania. This enabled Micromitra to reach up higher above the sea bed, and reduced the risk of mud and waste products entering between the two sides of the shell.