title: Ultrastructural analysis of nematocyte removal in Hydra.
abstract: A consecutive series of ultrathin sections through the distal one-third of a Hydra tentacle has revealed at least four categories of nematocytes: (1) normal, mounted nematocytes, in specific arrangements within the battery cells; (2) degenerating nematocytes, within the battery cells; (3) mature nematocytes, enclosed within endodermal cells: (4) a mature nematocyte, in the enteric cavity. The degenerating nematocytes within the battery cells and the nematocytes in the endoderm and enteric cavity appeared to be aging nematocytes undergoing death and removal. The results provide the first ultrastructural evidence for nematocyte degeneration within battery cells and also suggest phagocytosis of mature nematocytes by endodermal cells.
mesh_terms: D000818:Animals; D002470:Cell Survival; D004707:Endoderm / Q000166:cytology; D006829:Hydra / Q000166:cytology*; D007365:Intercellular Junctions / Q000648:ultrastructure; D008854:Microscopy, Electron; D010587:Phagocytosis