Notostomum cyclostoma, like all other leaches, has a basic outer body plan consisting of an anterior sucker containing the mouth, a body of 32 segments, and a posterior sucker containing the anus.  This particular species is approximately 8cm in length and about 5mm in diameter.  Color morphology includes a pink form and a purplish form. Both are seen in the picture, with darker blotches of color circling the animal. They spend their life living on marine fish such as sharks and rays, and deposit their egg cocoons on the carapaces of various species of crab in the northern Pacific Ocean.