redia:
an intramolluscan stage of digeneans, possessing a gut.
relapsing fever:
a bacterial disease characterized by repeated periods of fever and moderate mortality.
reticulocyte:
young erythrocytes that have recently lost their nucleus.
retroinfection:
a type of autoinfection whereby larval parasites just passed in the host's feces re-enter the anus and establish a new infection.
rhabditiform:
possessing an esophagus with a narrow central region and a terminal bulb.
ring stage:
the young trophozoite of Plasmodium spp., so named because a large central vacuole and peripheral nucleus give it the appearance of a signet ring.
Rocky Mountain spotted fever:
a rickettsial disease transmitted by ticks and characterized by an extensive rash.
rosette:
a posterior series of flaps, resembling the petals of a carnation, used as an organ of attachment by Gyrocotyle.
rostellum:
a central protrusion, eversible or not, on the scolex of some Cestoda.