The primary attachment organ on most digeneans is the acetabulum, or ventral sucker. It is a muscular sucker on the ventral or terminal region of the body, and is often ringed by small spines.
The acetabulum of Echinostoma is large, almost the diameter of the body.
The most common position of the acetabulum (A) is in the ventral midbody, termed a "distome" arrangement (distome means "two mouths", even though the acetabulum doesn't actually connect to the digestive system. Only the oral sucker (O) surround the mouth).
The "amphistome" arrangement has the acetabulum (A) at the posterior end of the body from the oral sucker (O).
The "paramphistome" arrangement has the acetabulum (A) at the opposite end of the body from the oral sucker (O), but in a subterminal position.
A few digeneans lack an acetabulum, an arrangement termed "monostome." Many of these live in the cecum, a location where attachment concerns are not as great as in the intestine.
