Studies on the tardigrades. II. Fine structure of the pharynx of milnesium tardigradum doyère

The fine structure of the pharynx and associated valve of the tardigrade Milnesium tardigradum is presented. The pharynx consists of a triradiate, cuticle lined lumen surrounded by radially arranged muscle cells and special apical cells which cap each of the ventricles of the lumen. The valve is an unusual structure marking the anterior limit of the pharynx. It is a specialization of the cuticular lining of the foregut and the apical cells of the pharynx. The significance and phyletic affinities of these structures are discussed.