Ultrastructural studies on the life cycle of a short-lived metazoan, Campanularia flexuosa: I. Structure of the young adult

Abstract

The ultrastructural morphology of 2-day-old Campanularia flexuosa hydranths was described. Each hydranth was comprised of an outer, ectodermal layer covered by a cuticle and an inner, gastrodermal layer, the two epithelia separated by the acellular mesoglea. Ectodermal cell types were: (a) nematocytes which include nematocysts with an apical triggering device, the cnidocil; (b) epitheliomuscular cells with highly vacuolated appearance and basal myofibrils; (c) secretory cells—type 1 with elaborate Golgi and associated vesicles, resembling neurosecretory cells; (d) secretory cells—type 2 with spherical compartments containing heterogeneous material; (e) interstitial cells studded with free ribosomes and a paucity of other inclusions. Gastrodermal cells in the solid tentacles were characterized by large central vacuoles and myofibrils adjacent to the mesoglea. Hydranth body gastrodermal cell types were: (a) mucous cells packed with pale, filamentous droplets; (b) zymogen cells filled with secretory granules; (c) digestive cells with apical food vacuoles and basal myofibrils; (d) secretory cells—type 2. The mesoglea, which penetrated deeply into both epithelia, consisted of a matrix containing a fibrillar network.