The ‘living-fossil community’ of the cyrtocrinid Cyathidium foresti and the deep-sea oyster Neopycnodonte zibrowii (Azores Archipelago)

摘要: Abstract From the steep submarine slope of southern Faial Channel (Azores Archipelago), a conspicuous archibenthic community two ‘living fossils’, comprising up to 30 cm sized deep-sea oyster Neopycnodonte zibrowii and sessile cyrtocrinid Cyathidium foresti , is described. Both thrive in particularly high densities concealed underneath bedrock overhangs 420–500 m water depth under comparatively stable environmental conditions (12.3 ± 0.25 °C open marine salinity). Other faunal elements include various sponges, bryozoans, serpulid worms, large barnacles. Submersible investigations showed that direct association C. N. not obligatory. The crinoid commonly encountered settling on dead as well live oysters, which provide benefits for terms substrate availability and/or participation oysters' active feeding current. upside down position both species provides protection from background sedimentation possibly shelter predators. After death partial disarticulation, crinoids are overgrown by other oysters or subsequent generations, mirroring limited availability. genera, represented type holopus Pycnodonte sp., respectively, also found fossils more than 60 million years old Middle Danian (Paleocene) Faxe Denmark. Associated with coral limestone, was occasionally impressive numbers either isolated substrata, such scleractinian corals, calyxes, – analogous Azorean occurrence inner surface pycnodontine oysters. Previous palaeohabitat models pseudoplanktonic attachment drifting wood cave ceilings photic reef, rejected favour an interpretation this thriving small hardground cliffs deep-shelf palaeoenvironment, associated cold- deep-water bioherms proposed recent palaeoenvironment assessments. We assume habitat-shift cyrtocrinids presumable shallow palaeoenvironments Late Cretaceous toward deep shelf setting Danian, reflects escape enhanced predation pressure during ‘Mesozoic Marine Revolution’. Sessile almost completely vanished waters were replaced mobile often strictly nocturnal comatulids. /( Neo ) pycnodonte did only survive Cretaceous/Palaeogene mass extinction, but whole Cenozoic can today be studied ‘living-fossil community’.