Anchoring cells (Desmocytes) in the hydrozoan polyp Cordylophora

Desmocytes or anchoring cells are present on the upright stolons of the athecate hydroid Cordylophora caspia and function to support the soft coenosarc within the rigid tube of perisarc by linking the perisarc with the mesoglea. These cells are characterized by accumulations of 70 A filaments which aggregate into dense rods at the apical end and contact the perisarc. At the base of the desmocytes the filaments are distributed within large cytoplasmic processes which interdigitate with an extension of the mesoglea. Desmocytes in Cordylophora are temporally and spatially formed in sequence as the upright elongates. Depending on their location and structure they can be categorized as forming, functional, or remnant desmocytes. The youngest, forming desmocytes are found in the distal end of the stolon 0.5-1.0 mm from the base of the hydranth. In this region coenosarc is just beginning to separate from the perisarc. Functional desmocytes are scattered 1-3 mm from the base of the hydranth and are associated with perpendicular extensions of the mesoglea. Remnants have lost their mesogleal connection and are located in more proximal, older regions of upright stolon. Support provided by the desmocytes to the upright stolon is limited by three factors that characterize the athecate hydroid: distribution of perisarc, pattern of growth, and extent of movement. The distal location of forming desmocytes is coincident with the hardening of new perisarc. The temporary nature of attachment sites is directly related to upright elongation. It is probable that the orientation of filaments within the cell and the mesogleal extension provide an addition feature of flexibility necessary to permit feeding, growth, and rhythmic pulsation movements characteristic of these hydroids.