Ultrastructural Development of the Excretory Bladder in Early Metacercariae of Ochetosoma aniarum

The excretory bladder epithelium of the Ochetosoma aniarum (Leidy, 1891) metacercaria undergoes drastic morphological changes within 24 hours of cercanal penetration into tadpoles. The previously smooth luminal surface develops numerous folds and lamellar structures. The spongiform granules so common in cercariae disappear, and simultaneously calcareous concretion formation begins. The concretions are seen to develop intracellularly and they do not appear to have a "nucleus" of membranous organelles. In an earlier study, Powell (1972) described the development of the excretory bladder in cercariae of Ochetosoma aniarum (Leidy, 1891). The cercarial excretory bladder lining was seen to be a secretory syncytium containing nuclei in cytoplasmic outpockets distal to the luminal surface, many spongiform secretory granules, mitochondria, rough endoplasmic reticulum, and Golgi complexes. The luminal surface of the lining was fairly smooth without any folds, microvilli, lamellae or other surface elaborations. As a continuation of that study, the early ultrastructural development of the metacercarial excretory bladder of Ochetosoma aniarum is herein reported. Materials and Methods Laboratory reared snails, Physella anatina, experimentally infected with Ochetosoma aniarum were used to obtain naturally shed cercariae which were placed in small finger bowls with laboratory reared Rana pipiens tadpoles. Cercarial penetration into tadpoles was observed by use of a dissecting microscope. Metacercariae were dissected out of tadpoles at intervals of 1, 4, 8, 12, 24, 48 hours and 3 weeks after cercarial penetration. Using microdissecting needles fashioned from sharpened insect pins, the metacercariae were excysted and prepared for electron microscopy using the techniques of Lumsden (1970). Sections were cut with glass or diamond knives on a Sorvall MT-2 ultramicrotome. Sections displaying silver or grey interference colors were picked up on naked or parlodion coated grids, double stained with uranyl acetate and lead citrate, and examined with a Siemens Elmiskope 1A operated at 80 kV.