How many lookalikes has Marionina argentea (Michaelsen, 1889) (Annelida: Clitellata: Enchytraeidae)? Three new species described from morphological evidence

Marionina argentea ( Michaelsen, 1889) is a taxon recorded throughout the Holarctic, from the warmer areas of the Mediterranean to all around the Arctic Ocean. However, following an in-depth and extensive comparative study (more than 100 specimens examined as permanent mounts, originating from the Mediterranean to Sweden), three species new to science have turned out to be hidden and confounded under its name. All of them are widely distributed in Europe. Marionina mendax sp. n. is mainly characterized by its large chaetal size, the coarse granulation of coelomocytes and the small penial bulbs. Marionina deminuta sp. n., in addition to its smaller body size and peculiar variation in the position of the genital organs (shifted cephalad by one segment in most specimens), consistently deviates from M. argentea sensu stricto in the pattern of the clitellum, the shape of the nephridia, and the relative size of the penial bulbs. Marionina mimula sp. n. differs from all the above species by having a posteriorly indented brain, a lumbricilline arrangement of the dorsal vessel, and a rosette of gland cells surrounding the spermathecal pore. The confused history and different interpretations of the diagnosis of M. argentea are reviewed and discussed. An interim revision of the morphological boundaries of the nominal species is proposed, pending re-examination of the type series of Enchytraeus argenteus Michaelsen, 1889.