摘要：Sessile encrusters with mineralised skeletons in the fossil record generally retain their original spatialrelationships to the substrate and each other. Being short living and not significantly time averaged,communities on shelly substrates represent excellent systems to study such relationships.Bryozoan and serpuloidean skeletobionts on molluscs and rhodolites from Lower Pleistocene localities inSicily have been studied. Species composition and specimen sizes testify to a short exposure of the shells onthe sea floor. Skeletobiont community structure is characterised by the dominance of a few species (5bryozoans out of 87 and 3 serpuloideans out of 17). Substrate coverage is usually low (<5%), rarely reaching50-60% or more. On bivalves, skeletobiont distribution does not exhibit a clear trend for inner/outer sides orleft/right valves.Oriented growths, differential patterns in microenvironment utilisation of the substrate and spatialcompetition have been analysed. Several of the recorded overgrowths resulted from superimposition ofspecimens growing on skeletons of previous, already dead encrusters. True competitive interactions mainlyinvolved bryozoans and only a few serpuloideans. Within bryozoans interspecific encounters usually led toovergrowth or abutment whereas intraspecific encounters commonly resulted in standoffs and growth side byside in cheilostomes, and to fusion of colonies in some cyclostome species.
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