|Collagen in the pterobranch coenecium and the problem of graptolite affinities
William G. Armstrong, P. Noel Dilly, and Adam Urbanek
Amino-acid analysis of the extracellular skeleton (coenecium) of two pterobranchs
(Hemichordata) Rhabdopleura normani and Cephalodiscus (C.) hodgsoni shows that both
contain considerable quantaties of collagenous material with relatively high hydroxyproline and
low hydroxylysine levels. The appearance of the fibrous material in the skeleton of
pterobranchs, although collagenous, differs from standard EM characteristics of collagen. The
fibrous material in the skeleton of Rhabdopleura and Cephalodiscus, although
compositionally collagenous in nature, lacks the characteristic ultrastructural features of most
collagen fibrils, especially thicker ones.
The identification of the collagenous nature of the pterobranch skeleton with the presumed
presence of collagen-like material in the periderm of fossil graptolites, taken in conjuction with
other data, supports the hypothesis that both groups may be closely related phylogenetically.
Published in Lethaia 1984, v. 17, pp. 145-152.