Abstract
A new species of parasitic isopod of the genus Metaphrixus Nierstrasz & Brender à Brandis, 1931 is described from one Hippolyte obliquimanus Dana, 1852 shrimp, collected in Costa Rica. It is the fifth species of the genus worldwide and the first record of the subfamily Hemiarthrinae from Costa Rica. A comparative table, an identification key and a distribution map for all species of the genus are also provided.