Diurodrilidae lack chaetae. "Diurodrilus species are nonsegmented, hyaline, dorso-ventrally flattened, marine metazoans with ventral ciliation and bilateral symmetry." "Diurodrilus has none of the significant annelid characteristics such as chaetae, head appendages, parapodia, nuchal organs, or obvious segmentation. Diurodrilus also lacks the characteristic midventral ciliary band found in many interstitial annelids such as Dinophilidae." Molecular analyses to date "do not support a close annelid relationship".