ABSTRACT
This chapter focuses on collagen at the biochemical level, in the context of its identification and characterization for comparison across phylogenetic lines. Collagen has the distinction of being the commonest protein in the animal world and it provides an extracellular framework for all multicellular animals. The chapter presents a study of invertebrate collagens and provides examples of the diversity of information that has ensued from detailed examination of many such collagens. As noted by M. B. Mathews, "there are four ways to study structures and forms in the biological world: comparative morphology, comparative embryology, comparative protein structure, and comparative DNA structure". The molecular studies are often quantifiable and allow for ready comparisons across broad phylogenetic domains. The collagen of echinoderms may be fundamentally similar to that of other animals, in the sense of containing subunits the size of conventional α chains. These subunits appear to be genetically distinct but have been incompletely characterized.
