Orchestia mauritanica sp. nov. (Amphipoda: Talitridae), a new sand hopper from Mauritania with a Comprehensive Key to the World Species of Orchestia

A new species of Orchestia Leach, 1814 is described based on two specimens sampled at the Banc dArguin National Park in Mauritania. The new species belongs to the group of Orchestia species with an irregular carpus on the seventh pereopod that includes also O. aestuarensis Wildish, 1987 and O. mediterranea Costa, 1853. Orchestia mauritanica sp. nov. can be distinguished from other group members by lacking a concavity on the posterior margin on the basis of the seventh pereopod and by having the posterior margin on the male second gnathopod with a straight distal margin followed by a proximal shelf. The species description is based on detailed illustrations and micro-CT imaging. An identification key to the Orchestia species of the world is provided.