The gastric mill on the genus Cyrtograpsus (Varunidae) has not been described previously. A morphological comparative study of the gastric mill ossicles within its species (C. angulatus, C. altimanus and C. affinis) was carried out. This research attempts to give new evidence to validate the existence of these three species and to serve as a guide to identify them. Urocardiac (dorsal median tooth shape), zygocardiac (shape and number of ridges and molar processes—cusps and plates—and their arrangement in the lateral teeth) and pectineal (number and shape of accessory teeth) ossicles, and cardiopyloric valve descriptions and comparisons are based on microscopical, stereomicroscopical, scanning electron microscope observations, and digital images. Morphological differences found in zygocardiac (lateral teeth) and urocardiac (dorsal-median tooth) ossicles allow to identify species. Considering these ossicles morphology in C. altimanus and C. affinis it can be concluded that the studied specimens belong to a single species as stated in morphometric and molecular comparative studies of the above species. These new data validate the existence of only two species (C. affinis and C. angulatus). This information will also be useful to recognize the species in the stomach content of their predators throughout the ossicles morphology.