Cylindroleberididae is a family of ostracods that shows remarkable morphological diversity. The defining feature is the possession of gills: 7–8 leaf-like pairs at the posterior of the body. Other features common to all species in the family include a "baleen-comb" on both the maxilla and the fifth limb, a sword-shaped coxal endite on the mandible, and the triaenid bristles on the basal endites of the mandible. A fossil discovered in 2003 with preserved soft parts has been assigned to the Cylindroleberididae. The fossil appears to have gills and is thought to date from 425 million years ago.