The attachment of collagenous ligament to stereom in primary spines of the sea-urchin, Eucidaris tribuloides.

Abstract The similar proximal and distal attachments to the stcrcom of primary spine ligament in the echinoid Eucidaris tribuloides are described, from thin sections and SEM studies on frozen and fractured spine articulations and ligaments from decalcified material. The orthogonal structure of the general stereom is modified on the attachment zones where bundles of collagen cylinders enter approximately hexagonally arranged channels. Straps of collagen extend in parallel scries between adjacent bundles via regularly placed ports and collagen loops rather than non-striated ‘tendons’ pass over skeletal trabeculac. The regular pattern of collagen straps is most evident on the proximal and distal attachment zones. Mechanical features of the nonadhesive mode of attachment are considered, together with similarities and differences between insertion of muscle cells and mutable eollagenous tissue (ligament) in echinoderms.