Pennella sagitta (L.) is redescribed from fresh specimens recovered from Histrio histrio (L.) and from material in the collection of the Smithsonian Institution. A small, delicate parasitic copepod, P. sagitta is shown to be a valid species, found only on fishes of the family Antennariidae. Attempts of earlier workers to synonymize P. diodontis with P. sagitta are rejected, and the distinguishing features of both species are presented. A neotype is proposed from material described herein, due to a lack of the original holotype. A provisional review of the genus Pennella Oken, 1816 is provided, and the taxonomic status of 31 species is discussed. Pennella exocoetus is described from material in museum collections. Seven species, P. balaenoptera, P. diodontis, P. exocoetus, P.filosa, P. instructa, P. makaira and P. sagitta are considered as valid members of the genus. The remaining species are reduced to synonymy with valid species or accorded the status of species inquirendae.