Buccal capsule and intestine ultrastructure of the marine predatory nematode Sphaerolaimus balticus (Monhysterida: Sphaerolaimidae)

Abstract

Summary The ultrastructural morphology of the buccal capsule and intestine (mid-gut) of the predatory marine nematode Sphaerolaimus balticus is investigated. The major part of the voluminous barrel-shaped buccal capsule is made up of strongly modified somatic cuticle and hence presents itself as an intricately differentiated cheilostome. The latter consists of three compartments: i.e., i) labial region; ii) striated region with six rows of fine longitudinal ribs; and iii) shagreen band penetrated by about ten projections of arcade tissue. The gymnostome and telostome are narrow and together constitute a small posterior portion of the buccal capsule. The mouth is evidently opened by contraction of anterior longitudinal somatic muscles. The intestine is characterised by a very thin and homogenous basal lamina. The cytoplasm of the enterocytes contains lipid granules, large electron-light vacuoles and rounded concentric inclusions in membranous vacuoles. Apical microvilli are separated from the lumen by a dense three-layered glycocalyx resembling the peritrophic membrane in the intestine of arthropods. The glycocalyx is only a supportive structure of the mid-gut. The most peculiar features of the intestine are the particularly strong junctions connecting the glycocalyx with the cells. The junctions appear as cytoplasmic bundles attached to the dense glycocalyx layer by dint of hemidesmosomes.