ABSTRACT
In Metacrinus rotundus (Isocrinida) the axial glandular organ is composed of epithelial tubules, the fine structure of which indicates a very active protein synthesis and export as well as storage of energy rich components (lipid, glycogen). Reichensperger’s organ is a connective tissue structure composed mainly of cells with well developed rough ER-cisterns and an active Golgi apparatus, embedded in a matrix of collagen and proteoglycans. Circumstantial evidence suggests that the cells may be both fixed and wandering cells. Axial glandular and Reichensperger’s organ are richly supplied with blood vessels and anatomically associated to form a common orally open bag-shaped structure enclosed in a continuous coelomic epithelium. The present electron microscopical study supports the view of Holland et al. (1991) that Reichensperger’s organ corresponds to the axial organ of the eleutherozoa, whereas the axial glandular tubules represent a special development confined to the crinoidea.
