Five new species of Monocelis Ehrenberg, 1831 (Platyhelminthes: Proseriata) from eastern Australia

Six species of the genus Monocelis Ehrenberg, 1831 have been found in eastern Australia. All are new to science. Five of them are formally described here. Three species (M. rupisrubrae sp. nov., M. nexilis sp. nov., and M. corallicola sp. nov.) have two clearly set pigmented eyespots lateral to the statocyst. They differ in details of the copulatory organ and karyotype. No clear synapomorphies among them or with other species of the genus could be detected. Monocelis beata sp. nov. and M. macrobulbus sp. nov. present extremely elongate, longitudinally oriented copulatory organs. They are sister species, and phylogenetic relationships with M. galapagoensis Ax and Ax, 1977 and M. hopkinsi Karling, 1966 are proposed. Australian Monocelis have distributions limited to recognized biogeographical provinces in eastern Australia: M. corallicola, M. beata and M. macrobulbus in the northern Australian Zone, M. rupisrubrae and M. nexilis in the ‘Overlap Zone’ of the central east coast and Monocelis sp. A in the southern Australian Region.