CONSTRUCTIONAL MORPHOLOGY AND PALEOECOLOGICAL SIGNIFICANCE OF 3 LATE JURASSIC REGULAR ECHINOIDS

General shape of test, spine and tubercle morphologies, and ambulacral pore characteristics of three regular echinoid species from the Upper Jurassic are interpreted in functional terms. Results are compared wi th independent sedimentological and palaeoecological analyses of the h ost sediments. In Acrociciaris nobilis the existence of a basal P3/4 i sopore phyllode suggests the development of a strong sucker disc which enabled firm attachment in a high energy hardground setting. This int erpretation is corroborated by tubercle characteristics indicating fir mly attached but largely immotile spines, forming a 'secondary test'. Morphological interpretation of Rhabdocidaris rhodani suggests a low e nergy, possibly partly dysaerobic, firmground setting as evidenced by (1) the exclusive occurrence of slit-like C isopores and (2) oblique t ubercles with a broad muscle attachment area indicating strong, motile stalking spines. Flattened general shape, lack of aboral spines and a fairly strong sucker disc enabled Glypticus hieroglyphicus to crawl a cross very irregular topography and even browse on the undersides of c orals or within an open coral framework. On the other hand, the fairly massive test suggests that elevated water energy occurred at least oc casionally, so that the host oligospecific dish-shaped coral associati on was probably positioned at shallower depths than previously thought . It is suggested that the adaptations of some Late Jurassic regular e chinoids to variable niches independently accompanied and mirrored sim ilar adaptive strategies developed in irregular echinoids, such as the evolution of respiratory flattened tube feet or adaptations towards s edimentation.