A new model organism among the lower Bilateria and the use of digital microscopy in taxonomy of meiobenthic Platyhelminthes:: Macrostomum lignano, n. sp (Rhabditophora, Macrostomorpha)

Macrostomum lignano n. sp. is a member of the Macrostomorpha, the basal-most subtaxon of the Platyhelminthes-Rhabditophora. This new species can be easily cultured in the laboratory and has been already the subject of several developmental/evolutionary studies. The small size, with only about 25 000 cells constituting the major bilaterian organ systems, makes this simultaneous hermaphrodite a possible candidate for a new model organism that is phylogenetically more basal than any of the model organisms currently used in such studies within the Bilateria. M. lignano belongs to the largest genus of the Macrostomorpha. Over 100 marine, fresh water and brackish water species are contained in the genus Macrostoinum, some of them with worldwide distribution pattern. Within it, M. lignano is a member of the M. tuba-species group, which we have summarized here. In the species description, we have used a novel approach to document such small soft-bodied meiobenthic organisms: we provide extensive digital micrographical documentation, which are deposited as a CD together with the type material.