They are planktic, swimming, or benthic, crawling on or in the mud on the bottom. Ostracodes are found throughout the world and include more than 50,000 species.
Many ostracodes eat decaying organic matter.
Some fish eat Ostracodes. As with all arthropods, ostracodes grow by molting. Most individuals will molt eight times before becoming an adult, leaving 8 sets of juvenile shells to collect in the sediment. The shells allow ostracodes to occur as fossils, since the shells tend to be preserved after the softer body tissues are lost. Ostracode fossils are easily identified to species, using shell characteristics.