The Collaborative International Dictionary
Coenurus
Coenurus \C[oe]*nu"rus\, n. [NL. fr. Gr. koino`s common + o'yra` tail.] (Zo["o]l.) The larval stage of a tapeworm ( T[ae]nia c[oe]nurus) which forms bladderlike sacs in the brain of sheep, causing the fatal disease known as water brain, vertigo, staggers or gid.
Note: This bladder worm has on its surface numerous small heads, each of which, when swallowed by a dog, becomes a mature tapeworm in the dog's intestine.
Wiktionary
coenurus
n. The parasitic larval stage of tapeworms; they infest herbivores