‘Endless forms most beautiful’: taxonomic revision of the planarian Geoplana vaginuloides (Darwin, 1844) and discovery of numerous congeners (Platyhelminthes: Tricladida)

In 1832, Darwin discovered two elegantly coloured true Planaria in Rio de Janeiro, one of which he later formally named as Planaria vaginuloides (Darwin, 1844). Currently named Geoplana vaginuloides (Darwin, 1844), it is the type species of the genus and of the subfamily Geoplaninae. Many chromatic patterns of the body were recorded for the species, but its polyphyletic status was recently pointed out. Herein we revise the three-species-rich genus by combining morphological and molecular data within an integrative taxonomic framework. Our results support the monophyly of the genus, but also reveal that there are at least four nominal species recorded in the literature under the name of G. vaginuloides. This number increases to ten if the diagnostic features used by former authors are applied, i.e. the eye-catching dorsal colour pattern and the typical, extraordinarily long penis papilla. Our results also indicate that Geoplana chita Froehlich, 1956 is a complex of species and that Geoplana pulchella Schultze & Mller, 1857 is monophyletic. We describe herein 13 species of the genus. Surprisingly, the number of species of Geoplana was overshadowed by their beauty.