Primisanguis caribbeanensis n. gen., n. sp. (Digenea: Aporocotylidae) infects the stoplight parrotfish, Sparisoma viride (Bonnaterre, 1788), (Labridae: Scarinae) in the Caribbean Sea off La Parguera (17°58'26" N, 67°02'47"W), Puerto Rico. It is most easily distinguished from other nominal aporocotylids by the combination of having an adult body that is approximately 5-10 times longer than wide, a sinistral posterolateral body protuberance, tegumental body spines that are straight (lacking recurved tip) and wrap dorsoventrally around the body margin, posterior ceca that are 2-5 times the anterior ceca length, a single testis that extends lateral to both the ceca and nerve cords, an ovary abutting the posterior margin of the testis, a symmetrical vitellarium and medial primary vitelline duct, a post-cecal and post-gonadal ootype, and a proximal uterus that is extensively convoluted posterior to the ootype and which functions as a uterine seminal receptacle. The new genus lacks a spinous anterior sucker, pharynx, auxiliary external seminal vesicle, cirrus stylet, oviducal seminal receptacle, and Laurer's canal. The new species is morphologically most similar to the other aporocotylids that have a posterolateral body protuberance, including species of Psettarium Goto and Ozaki, 1930, Aporocotyle Odhner, 1900, Ankistromeces Nolan and Cribb, 2004 , Phthinomita Nolan and Cribb, 2006, and Littorellicola Bullard, 2010, but it can be differentiated from them, at the least, by lack of a spinous anterior sucker in the adult and by the combination of having dorsoventral rows of tegumental spines, a testis dorsal to the posterior ceca, and a uterine seminal receptacle posterior to the ootype. The new species is the first aporocotylid reported from the Caribbean Sea or from a parrotfish of Sparisoma.