Variations morphologiques et adaptations morphofonctionnelles chez les ostracodes: Signification environnementale

Abstract

Ostracodes present a diversity and a variability affecting their distribution as well as their morphology, which reflect with accuracy and reliability the characteristics and the fluctuations of marine and continental biotopes. An inventory of variable morphologies and their relationships with the adaptation of biological and physiological functions (morphofunctional aspect) is undertaken, using chosen examples in post-paleozoic times. The considered morphological elements are as follows: central muscle scars pattern, marginal zones and vestibule (internal characters), size, carapace geometry, ocular tubercles, external ornamentation, normal pore canals. In recent and past environments, each of the considered elements and/or the combination of several of them, is used to trace one of some parameters, generally interdepending on the environment: hydrological, physico-chemical, trophic, dynamic and climatic parameters. For example, there are relationships between the variation of the valve reticulation and carbonate equilibrium at the water-sediment interface; nodation is an indication of low salinity or of an enrichment in allochtonous organic matter; the presence and development of an ocular tubercle is characteristic of life in the photic zone; the size of the vestibule in some species is related to the oxygene concentration. In conclusion, the reliability limits for application of available informations are discussed and future prospects evolved.