Palaeobiology of Floricolumnus (col.) girvanensis Donovan & Clark (Crinoidea, Silurian) from the Girvan District, Ayrshire
Fossil crinoids are only rarely described from complete skeletons, that is, from the attachment structure to the ends of the arms. The crinoid Floricolumnus (col.) girvanensis Donovan & Clark was originally described on the basis of its distinctive column only, particularly the inflated, serrated nodal columnals; the crown remains unknown. Floricolumnus (col.) is important, with nodal columnals representing potential intercontinental stratigraphic markers for the interval from the Lower-Middle Llandovery boundary to the mid-Middle Llandovery (that is, late Rhuddanian to mid-Aeronian). The discovery of the attachment structure of F. (col.) girvanensis is, therefore, significant. A long pluricolumnal is interpreted as a distal planar coiled attachment; a simple discoidal holdfast with an anastomosing sculpture may be a juvenile attachment. Erect protuberances on some nodal epifacets may be a stereomic reaction to embedding or boring epizoobionts.