Zoology Publications from Victoria University of Wellington—Nos. 58 to 61
The histology and histochemistry of the gymnoblastic hydroid polyp Syncoryne tenella (Farquhar, 1895) is described. The perisarc at the hydranth base is composed of an inner layer of a proteinaceous substance and an outer layer of acidic mucopolysaccharide. The hydranth is closely invested by a thin periderm of mucoprotein which is continuous with the inner perisarc layer of the hydrocaulus. The epitheliomuscular cells of the ectoderm of the hydranth contain mucoprotein secretory granules. The hydranth endoderm is differentiated into apical, middle, and basal regions. These are specialized for secretion of lubricating substances, for intracellular and extracellular digestion, and for intracellular digestion respectively. Gland cells present in the middle region are similar morphologically and histochemically, and probably functionally, to vertebrate pancreas acinar cells. Migration of cnidoblasts through the ectoderm of hydrocaulus and hydranth is proposed to explain their distribution in mature individuals. A new interpretation of the cells forming the core of solid tentacles is given. The mesogloea is commonly fibrous. It contains acidic mucopolysaccharide and mucoprotein.