Ultrastructural observations on some dendroid and graptoloid graptolites and on Mastigograptus

The ultrastructure of the dendroid genera Acanthograptus, Dendrograptus, Desmograptus, Ptilograptus and Dictyonena, the genus Mastigograptus, and the graptoloids Monograptus, Cyrtograptus, Neogothograptus, Paraplectograptus and Sokolovograptus is described. The cortical fibrils of most of the taxa bear a clockwise spiral ornament. There is a striking similarity between the cortical fabric of Dictyonema sp. and the extracellular plies of collagen recognized in extant metazoans. Cortical fibrils may be considered a collagen-like material and the matrix may be compared with a polysaccharide - protein complex. The matrix in Dictyonema and Ptilograptus is formed of regularly spaced interconnecting rods. However, the interconnecting rods are a feature external to the cortical fibrils, and therefore their spacing constitutes only an indirect evidence for the fibrils being formed of a collagen-like material.