Comparative ultrastructural study of the lemnisci in larvae and adults of Centrorhynchus milvus Ward, 1956 (Acanthocephala, Centrorhynchidae)

Abstract

The lemnisci of acanthocephalans are enigmatic organs which, except for those of adult Moniliformis dubius and Octospinifer macilentus, have not been described on the basis of examination by electron microscopy. We were able to study them in cystacanths, juveniles, and adults of Centrorhynchus milvus. They show a fibrous outer layer covering an amorphous layer; the latter is in close contact with a lining plasma membrane perforated by numerous pores which communicate with an equal number of small vesicles in cystacanths, with endocytotic vacuoles in juveniles, and with canaliculi in adults. In the center of each lemniscus are large nuclei surrounded by a common cytoplasm containing large protein granules. Only the lemnisci of cystacanths encysted in wood lice exhibit a large network of microfilaments at their center.