A viviparous hoplonemertean, Prosorhochmus chafarinensissp. nov., is described from the Chafarinas Islands (western Mediterranean). The species lives in the low eulittoral under the encrusting alga Lithophyllum lichenoides. Prosorhochmus chafarinensis is compared and contrasted in detail with the other valid members of the genus, P. claparedii from European waters, P. americanus from South Carolina, and P. adriatica from Italy.