This slide shows male and female dog hookworms (Ancylostoma caninum). The male is easily recognized by its conspicuous copulatory bursa, an expanded posterior portion of the worm used for grasping the female during mating.  Several species of hookworms infect over a billion people in warmer regions of the world, including the southeastern United States.  Juvenile parasites gain entrance their hosts (often barefoot children) by burrowing through the skin.  Note the mouth with hook-like cutting teeth that are used to attach to the wall of the intestine where they feed on blood.  Heavy infestations can cause anemia, malnutrition and retarded development.