Morphological stasis in an old and widespread group of species: Contribution to the taxonomy and biogeography of the genus Girardia (Platyhelminthes, Tricladida, Paludicola)

Abstract

Material is described that contributes to our understanding of the anatomy of 11 species of the genus GirardiaBall, 1974 and the taxonomy of one species of RomankenkiusBall, 1974. Apart from recently collected specimens, the study for the first time details old syntype material that was recovered for the species G. anceps and G. andina, resulting in the first modern description of the last-mentioned species. Relatively recently collected specimens from new sampling sites are described for G. chilla, G. dorotocephala, G. festae, G. paramensis, and G. tigrina. The new records for G. festae considerably enlarge the known geographic range of this species in South America, particularly east of the Andes. It is shown that contrary to the opinion of earlier workers there is some slight, but invariable, anatomical difference between North and South American specimens of G. tigrina, with the Neotropical animals having a much more muscled bursal canal. This slight anatomical difference suggests that the North and South American forms are actually sibling species. Four new Girardia species are described, three for the South American continent (G. avertiginis, G. capacivasa, G. jugosa) and one from Jamaica (G. bursalacertosa). The study confirms earlier conclusions that generally species of Girardia are anatomically very similar and that therefore species recognition can be difficult. It is striking that taxonomic diversity in the Neotropical Region is low, in that the majority of the freshwater planarians belongs to a single genus, viz. Girardia. It is concluded that Romankenkius michaelseni (Böhmig, 1902) is a junior synonym of R. patagonicus (Borelli, 1901).