Electron Microscope Studies of the Muscle and Hook Systems of Hatched Oncospheres of Hymenolepis citelli McLeod, 1933 (Cestoda: Cyclophyllidea)

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Abstract
The morphology of the hook and muscular systems of hatched oncospheres of H. citelli was studied by electron microscopy. The oncosphere is covered by an outer coat of cyto-plasmic material which forms extrusions and ballooning regions. A basal laminalike structure, below the outer coat, encircles the oncosphere and serves as a point of muscle attachment. Transverse somatic myofibers almost entirely cover the oncosphere. Hook musculature attaches only to the connective tissue of the bases and collars of the hooks. The bases of each lateral hook pair are joined by a common zone of connective tissue whereas the medial hook bases are embedded in individual cups of this material. Lateral hook base musculature extends anteriorly and posteriorly in wide bands to the basal lamina. Some of these posteriorly directed muscles unite ventral to the medial hooks. Opposing sets of collar muscles arise from each hook. The hook is composed of 3 layers. An outer layer extends from the base and includes the collar. A middle fibrous layer extends from the base to the tip of the hook, as does the crystalloid central core. Those areas in the oncosphere not taken up by hooks and muscles are filled primarily with gland material and nuclei.