Dog tapeworm. Coloured scanning electron micrograph (SEM) of the head of a dog tapeworm (Echinococcus granulosus), showing the hooks it uses to cling to its host. Tapeworms are parasitic flatworms that live in the digestive tract of their vertebrate host. E. granulosus is a cyclophyllid cestode worm that parasitises the small intestine of canids as an adult. However, it has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. Magnification: x700, when printed 10 centimetres wide.