Digeneans use oral and ventral suckers for attachment, locomotion, and feeding. The structure of these organs is rarely described in detail. I used fluorescent actin staining and confocal laser scanning microscopy to describe musculature arrangement in the oral sucker of eight digenean species (all Plagiorchiida). Scanning electron microscopy and light microscopy of histological sections were used for a general morphological description of the sucker structure. The musculature of the oral sucker is independent from the body wall and the internal muscles. The arrangement of the muscles within the oral sucker is complex; it includes up to 14 groups. Layers of transverse and meridional muscle fibers line the outer surface beneath tunica propria. Transverse muscle bands, meridional fibers, anterolateral groups, and circular or semicircular fibers of the sphincter are present at the rim of the oral sucker. Circular and longitudinal muscle fibers are found beneath the tegument of the buccal cavity. The bulk of the sucker consists of radial muscle bundles, but it also contains chordal muscle bundles, diagonal fibers, and wide lateral muscle bands. Based on the results, I propose that three features determine the complexity of musculature arrangement in the oral sucker: (1) bilateral symmetry of the sucker, (2) incongruity of the main body axis and the own axis of the sucker, and (3) regionalization of the sucker surface. The origin and functioning of the oral sucker are discussed.
Krupenko, D. (2019). Oral sucker in Digenea: structure and muscular arrangement. Zoomorphology, 138(1), 29–37. https://doi.org/10.1007/s00435-018-0423-x