ABSTRACT Isimerope semele n. gen. and n. sp., a valvatiform hydrobiid from southern continental Greece, is described based on morphological and molecular data. Isimerope is distinguished from other European and circum-Mediterranean valvatiform hydrobiid genera by a unique combination of morphological characters, including distinctive male and female genitalia. Isimerope is differentiated from morphologically similar Graecoarganiella, which is also endemic to Greece, by a 10.15% mean COI sequence divergence. Isimerope semele is composed of three small populations living in disturbed habitats, including springs and a river
