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Convergent morphology in small spiral worm tubes (‘ Spirorbis ’) and its palaeoenvironmental implications

2006; Geological Society of London; Volume: 163; Issue: 2 Linguagem: Inglês

10.1144/0016-764905-145

2041-479X

Paul D. Taylor, Olev Vinn,

Marine and environmental studies

Calcareous tube-worms generally identified as Spirorbis range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent Spirorbis is a polychaete annelid, details of tube structure in pre-Cretaceous ‘ Spirorbis ’ suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true Spirorbis . Recent Spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian–Triassic. Anomalies in the palaeoenvironmental distributions of fossil ‘ Spirorbis ’ are explained with the recognition of this striking convergence between microconchids and true Spirorbis .