Achaeta unibulba sp. n. is described from a variety of terrestrial habitats in Europe. The new species is similar to a group of species around A. eiseni Vejdovský, 1878, having bottle-shaped glands (= setal follicles) dorsally and ventrally, the latter being only slightly smaller. Its main distinguishing characters are the fused penial bulbs forming a large roundish body at the ventral midline, the absence of accessory penial glands, the arrangement of clitellum glands, the presence of a large gland at the orifice of the spermathecae, an oesophageal appendage in V without canal leading to pharynx, and the presence of three pairs of preclitellar nephridia. The species occurs in slightly acid to neutral soils. It was found in mineral horizons of mull humus forms as well as in fen peat.