Electron micrographs of a hydroid (Zanclea margaritae) desmocyte within the epidermal tissues adjacent to the skeletal material of the coral, Acropora muricata.
(A) The desmocyte is positioned within the epidermal cell layer, connected to the mesoglea by an extension of the collagenous layer. (B and C) Tonofibrillar rods at the apical end of the desmocytes are transversely striated, perpendicular to the fibres. The rods extend outwards from the apical surface in to an extracellular organic layer adjacent to the carbonate skeleton. (D) Fibrous mesogleal material extends through the interstices of the highly bifurcated distal portion of the desmocyte. he, hydroid endoderm; hm, hydroid mesoglea; hp, hydroid epidermis; eom, extracellular organic material; r, rod; dpm; desmocyte plasma membrane; mc, mesogleal channel. Scale bars: A = 5 µm; B–D = 500 nm.