Organomineralization of cirratulid annelid tubes - Fossil and recent examples

Abstract

The calcareous housing tubes of fossil species of the polychaete worms Diplochaetetes and Dodecaceria from the Tertiary of Lower California (Mexico) are composed, as well as the tubes of recent species of Dodecaceria, by micritic, peloidal lamellae. The wall of Diplochaetetes spp. consists of only a few, that of Dodecaceria spp. of numerous lamellae. They form a stromatolitic fabric with intercalated lenses of fibrous calcite/aragonite. Histological investigation of the tubes of Dodecaceria showed that the tube formation is related to two processes. The initial process is weakly controlled by the worm itself (matrix mediated). The worm produces acidic organic mucus substances which are enriched between the soft tissue and the tube wall. The entire mucus inhibits the mineralization of the mucus for a certain time. The mineralization events of the mucus are responsible for the stromatolitic microfabric. Within the spaces between the primary lamellae non-specific EPS (extracellular polymeric substances) -rich mucus is enriched, which controls the formation of fibrous aragonitic crystals and peloidal fabrics. This is a very characteristic organomineralization process which is not controlled directly by the organism. The entire process is comparable with those seen in complex rigid modern microbialites from salt and alkaline lakes in Western Australia and Nevada.