Lumbriculus kareliensis, an Annelid worm, was described by Popchenko in 1976 from material collected in Karelia. It is distinguished from other species in the genus by the position and shape of the atrium, which is large and kidney-shaped, reaching form the male pore in segment X into segment XI. Unlike all other Lumbriculus species, the ovary is located two segments posterior to the atrium. The spermathecae are oval, and positioned dorsally.