[The oral sucker muscles of six representatives of the order Paramphistomatida (Plathelminthes, Trematoda)].

The spatial arrangement of muscles in the oral suckers of six trematode species belonging to five families of the order Paramphistomatida is described. The functional load and adaptive significance of different muscle groups in the suckers themselves and the associated structures--preoral lip and muscular cap--are discussed. Complete section series in three projections have been examined; this demonstrates the presence of previously unnoticed structures, namely, semicircular and diagonal muscles, regulating shape of the oral cavity, and short longitudinal muscles, acting as a sphincter, as well as localization of the largest internal muscles on the sucker lateral sides. It has been shown that the presence of internal longitudinal muscles suggests that the organs in question are closer to the oral suckers of other trematodes rather than to their pharynxes.