Annotated checklist of the umagillid turbellarians infesting echinoids (Echinodermata)

A literature survey of the taxonomically complex taxon Syndesmis Silliman, 1881 is presented, resulting in the recognition of 22 valid species and three species mentioned in several works but not yet described. For each of these species the host(s) are mentioned and the distribution is given. These results are compared with earlier checklists and the differences are discussed.