Specimens belonging to a new species of Perinereis Kinberg, 1865 were collected from natural oyster reefs in an estuarine environment on Florida’s southwest coast. The genus Perinereis includes more than 60 species, of which, P. aibuhitensis (Grube, 1878), P. brevicirrata (Treadwell, 1920), P. camiguinoides (Augener, 1922), P. jascooki Gibbs, 1972, P. kuwaitensis Mohammad, 1970, P. singaporiensis (Grube, 1878), P. vancaurica (Ehlers, 1868) and the new species have two short bars on Area VI and notopodial dorsal ligules that are not greatly expanded. The most geographically close species is P. brevicirrata. The new species can be distinguished from P. brevicirrata by the absence of a notopodial prechaetal lobe, Area V with 3 cones in a triangle, and Area VII-VIII with two well-defined rows of 33 paragnaths, the basal rowlonger paragnaths in relation to the distal ones. The new species resembles P. singaporiensis based on the absence of notopodial prechaetal lobe; however, the two species differ in some morphological characteristics such as tentacular cirri length, shape of dorsal notopodial ligules, and falciger blades. A key to all American species of Perinereis is included.