Hemicyclops columnarissp.n. is described from the scleractinian coralPorites lobataDana on the Pacific coast of Panama. The new species may be distinguished from its 23 congeners by a combination of the body size and the shape of the genital segment in the female. Although certain members of the genusHemicyclopsare associated with crustaceans, polychaetes and other marine invertebrates, this is the first record of a species of this genus from a hard coral.