Oncosphere muscles

The process of hatching in the Cyclophyllidea, which results in the release of the oncosphere, has been discussed in Chapter 7. The basic structure of a mature oncosphere (Fig. 8.16), which will not be discussed in detail here, does not vary substantially between species. It is composed essentially of (a) a thin covering epithelium with cytoplasmic extensions, (b) an additional complex system of muscles operating the three pairs of hooks, (c) a pair of large penetration glands, (d) a small core of germinative cells from which the next larval stage develops and (e) a primitive nervous system. 

The cyclophyllidean oncosphere is well supplied with musculature and the general pattern of muscles appears to be similar in most species. So in both Hymenolepis citelli (which penetrates an invertebrate gut) and E. granulosus (which penetrates a vertebrate gut) there are 16 somatic muscle cells (146, 839). However, E. granulosus has 16 hook muscle cells but H. citelli has only 13. In E. granulosus, the hook muscles have been shown to insert at the collar and base of the hooks and at the basal lamina of the embryonic epithelium. Each pair of hooks has three muscle systems associated with it (a) a protractor system, for hook extensions (b) an abductor system, which draws the hooks together and (c) a retractor system which pulls the hooks into the body (839). 

Collin, W. K. (1968). Electron microscope studies of the muscle and hook systems of hatched oncospheres of Hymenolepis citelli McLeod, 1933 (Cestoda Cyclophyllidea). Journal of Parasitology, 54 74-88. 

Echinococcus granulosus hook-muscle systems and cellular organization of infective oncospheres. International Journal for Parasitology, 13 289-99. 

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