ABSTRACT
A semi-quantitative study of stereom microstructure in plates of over 50 species of Echinoderms, including Echinoids, Ophiuroids, Asteroids and Crinoids, identified eight basic three-dimensional stereom fabrics. Using a combination of histological and growth zone data, it is possible to show that stereom microstructure is controlled largely by two interacting factors : the rate of plate growth and the nature of the associated soft tissue. Variation in the rate of growth produces stereom banding. Collagenous fibres inserting into actively growing surfaces produce galleried stereom but where growth rate is slow or periodically ceases collagenous fibres are associated with a labyrinthic stereom.
