Suckers are circular organs that aid attachment by adhering to some surface on the host. They do not penetrate host tissues. Suckers may occur in various arrangements. They are usually under muscular control.
Muscular suckers are common on platyhelminths.
Modified mouthparts form a sucker (arrow) on Argulus.
A sucker in action. Proteocephalus attaching to the intestine of its host. The arrow shows how the sucker may pinch in a bit of host tissue but does not damage it.
Loculi are shallow depressions that do not have strong muscular development, so they tend to act passively, much as a suction cup does.
Locule (L) in the scolex of Cyathocephalus.
Locule (arrow) in the ventral sucking disk of Cotylaspis.
