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.
___________________________________________________________________________
GRAPTOLITE NET
edited by
Piotr Mierzejewski, the Count of Calmont and Countess Maja A. Korwin-Kossakowska
2002-2003
Fibrillar nature of the common coenecial tissue in Cephalodiscus solidus.
SEM micrograph by: Piotr Mierzejewski

Related pages:
Cortical bandages in Orthograptus gracilis      Graptoloid zooid