Ultrastructural Changes in the Body Wall of Neoechinorhynchus cylindratus (Acanthocephala) Associated with Reproductive Activity

The ultrastructure of the body wall of Neoechinorhynchus cylindratus is described for the first time. It is similar to that of Octospinifer macilentus, the only other eoacanthocephalan studied, and not significantly different from that of Archiacanthocephala and Palaeacanthocephala. The longitudinal muscle layer in juveniles characteristically contains ovoid giant nuclei that, in fertilized worms, become associated with spheroid structures provisionally termed membrane-forming bodies. The latter are comparable to the wall-forming bodies of other biological systems. The spheroid double membrane-bounded bodies are highly osmiophilic initially, probably of glycoprotein/Golgi origin, that granulate subsequently and then degranulate as they appear to form the expanded elongate-lobulated giant subcuticular nuclei characteristic of mature adults. The process of nuclear membrane formation is similar to that described in post-fertilization stages of many species of coccidians, e.g., Eimeria truncata and Eimeria nieschulzi, as well as in some mammalian systems such as rat bladder. The highly enfolded fenestrated giant nuclear membrane in young fertilized females of N. cylindratus may have a secretory function related to physiological processes involving the production of sex cells.