A new Brazilian endemic Monanchora is described, M. brasiliensis sp. nov. It is clearly distinct from any other species in the genus by the monodentate shape of its anchorate isochelae, and its smooth, centrotylote and strongyloid microrhabds. Monodentate anchorate isochelae are relatively common, normally abundant, and represent the main diagnostic character for recognizing the new species, but microrhabds are usually rare and may be even absent. Monanchora brasiliensis sp. nov. can be further differentiated from other Atlantic species of the genus in eventually showing tetralobate branches and a skeleton formed by well-defined honey-coloured spongin fibres. The affinities of the new species with other crambeids and the nature of anchorate isochelae, microrhabds as well as the megascleres in defining Monanchora are discussed. An amended diagnosis for the genus is proposed.
