A sucker in the form of a groove such as is seen on either side of the head of Diphyllobothrium latum; the broad tapeworm or fish tapeworm, a large worm found in the intestines of humans, cats, dogs, mink, bears, and other fish-eating mammals, sometimes reaching a length of nine meters.

Its head has two grooves, or suckers (bothria). It has two intermediate hosts; the first, a crustacean; the second a fish.

Human infection, acquired by eating inadequately cooked fish, may have a clinical picture like that of pernicious anemia.