Ultra-Structure of the Choanocyte Collar-Cells in Freshwater Sponges

Abstract

As early as 1896 Bidder¹ mentioned the presence of fibrils in the collars of the relatively large collar cells of calcareous sponges. Later, the very existence of such a structure was denied by several authors though confirmed by a few, particularly De Saedeleer² and Dubosq and Tuzet³. Kilian⁴ has succeeded in demonstrating the existence of fibrillar structures in the much smaller collars of siliceous sponge collar cells. That author observed by means of the electron microscope, whole Spongillidae collar cells which were previously dilacerated and fixed. Yet he stated himself that the fixatives he used caused severe contractions of the collars. De Saedeleer² is the only one who suggested that the collar should be considered as an ‘eel-trap’ made up from separate tentacles.