Phagocytic activities of the gorgonian coral Swiftia exserta

The cellular response component of body defense in gorgonians and other cnidarians is thought to be carried out by cells with phagocytic capabilities. To test for the phagocytic character of cells, the introduction of foreign particles was employed and observed in both living cells and histological preparations of the gorgonian coral Swiftia exserta. Observations of untreated tissues revealed normal cells and tissue morphologies. A microscopic observation of living cells following the introduction of particles in a cut revealed that only a mixed population of colorless cells phagocytized the particles. Also particles or clumps of particles were seen on the surface of the colorless cells. Subsequent histological observations allowed identity of colorless cells to be inferred as granular amoebocytes, ectodermal cells, and gastrodermal cells. Cells stained for localization of peroxidase (indicative of phagocytic activity) demonstrated the presence of peroxidase-positive cells. Histological preparations revealed that major phagocytosis of particles was associated with tissue trauma. When particles were introduced by means of a cut or inserted thread, phagocytic activity was detected within 2 h. However, it was confined to the granular amoebocytes in the immediate site of trauma. After 24 h, extensive phagocytosis spread throughout a relatively large area surrounding the wound. At that later time, phagocytic cell types included granular amoebocytes, epidermal cells, sclerocytes, mesogleal cells, and gastrodermal cells of the solenia. Observations suggest that trauma induces phagocytosis in cells not normally phagocytic in S. exserta. No localization of phagocytic cells and no mitotic cells were observed at either 2 or 24 h after particle introduction.