Integrative morphological and molecular investigation of Turbanella hyalina Schultze, 1853 (Gastrotricha: Macrodasyida), including a redescription of the species

While morphometric and meristic variation of T. hyalina broadly overlaps with other congeneric species, our light and electron microscope data bore the presence of up to twelve pairs of reduced ventral adhesive tubes on the posterior trunk section, possibly an autapomorphic and hence diagnostic character of T. hyalina. Furthermore, we were able to prove the absence of a pair of ventral 'cirrata tubes' that is present in similar species of the genus. The myoanatomy exhibits several similarities but also distinct differences compared to other con-generic species. Our mtDNA survey uncovered more intraspecific genetic diversity than previously known. However, the data also demonstrate that populations of different northwest European sites belong to the same species. The observed phylogeographic patterns are possibly related to post-glacial population expansions in the studied area and may already demonstrate a certain restriction of the gene flow.