A new genus, Plesiomenaeus, is designated for a new species of sponge associated pontoniine shrimp, P. poorei, from Zanzibar, which is described and illustrated. The new genus resembles Periclimenaeus Borradaile, from which it is distinguished particularly by the lack of a molar process and fossa on the fi ngers of the major second pereiopod. Plesiomenaeus poorei also closely resembles Periclimenaeus bouvieri (Nobili) and the relationship is discussed.