A peculiar bored crinoid from Salthill Quarry, Clitheroe, Lancashire (Mississippian; Tournaisian), UK

摘要

Salthill Quarry, Clitheroe, Lancashire, is a Site of Special Scientific Interest (SSSI) and important for its Mississippian (Tournaisian, Chadian) crinoids. A pluricolumnal, Pentagonocyclicus? (col.) sp., preserves multiple pits, Oichnus paraboloides Bromley. Pits on one side of the specimen sit atop cyst-like structures and infested the crinoid when it was alive; the protuberances represent a growth reaction. At the time, the column was either upright, pits concentrating on one side presumably in response to current direction, or recumbent (and distal). Pits on the other side engendered no growth reactions; the crinoid was dead and lying on the sea floor when infested. The infestation of the live crinoid must be considered ectoparasitic.