Oral sucker in Digenea: structure and muscular arrangement
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.
KeywordsDigenea Musculature Oral sucker Platyhelminthes
I am grateful to Dr. George Slyusarev for his help with the sampling, and to Andrej Dobrovolskij and Anna Gonchar for the revision of the manuscript. I also would like to thank the anonymous reviewer for thorough revision of the manuscript, helpful comments and very precious ideas for the Discussion. This research would have been impossible without the facilities of Educational and Research Station “Belomorskaia” (Marine Biological Station) of Saint Petersburg State University and Laboratory of Algology of Murmansk Marine Biological Institute. The confocal microscopy studies were carried out using the equipment of research resource center “Molecular and Cell Technologies” of Saint Petersburg State University, and the SEM studies—in the Centre of Collective Use “TAXON”, Zoological Institute RAS. The reported study was funded by Russian Foundation for Basic Research, according to the research project No. 16-34-60156 mol_а_dk.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
Conflict of interest
The author declares that she has no conflict of interest.
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