ULTRASTRUCTURAL-CHANGES IN THE BODY-WALL OF NEOECHINORHYNCHUS-CYLINDRATUS (ACANTHOCEPHALA) ASSOCIATED WITH REPRODUCTIVE ACTIVITY

The ultrastructure of the body wall of Neoechinorhynchus cylindratus i s described for the first time. It is similar to that of Octospinifer macilentus, the only other eoacanthocephalan studied, and not signific antly different from that of Archiacanthocephala and Palaeacanthocepha la. The longitudinal muscle layer in juveniles characteristically cont ains ovoid giant nuclei that, in fertilized worms, become associated w ith spheroid structures provisionally termed membrane-forming bodies. The latter are comparable to the wall-forming bodies of other biologic al systems. The spheroid double membrane-bounded bodies are highly osm iophilic initially, probably of glycoprotein/Golgi origin, that granul ate subsequently and then degranulate as they appear to form the expan ded elongate-lobulated giant subcuticular nuclei characteristic of mat ure adults. The process of nuclear membrane formation is similar to th at described in post-fertilization stages of many species of coccidian s, e.g., Eimeria truncata and Eimeria nieschulzi, as well as in some m ammalian systems such as rat bladder. The highly enfolded fenestrated giant nuclear membrane in young fertilized females of N. cylindratus m ay have a secretory function related to physiological processes involv ing the production of sex cells.