New information on the morphology and skeletal ultrastructure of the Ordovician cyclostome bryozoanKukersella Toots, 1952

Well preserved specimens of Kukersella from the Late Ordovician (Ashgill Series) of South Wales have enabled a re-evaluation of the morphology and skeletal ultrastructure of the genus. They reveal that the endozone forms an axial bundle and the endozonal zooecia are not proximal portions of the exozonal zooecia; the endozone is also found to be absent in the encrusting bases of colonies. Examination of the preserved skeleton has led to interpretations on the soft part morphology of Kukersella. New zooids were budded at the distal growing tip beneath a pseudocoelomic sac. Interzooidal pores in the exozone allowed a free exchange of pseudocoelomic fluids between adjacent exozonal zooids (autozooids). Endozonal zooids would have had short living-chambers and are interpreted as possible kenozooids; their function may have been structural. The ultrastructure, examined using the SEM, is composed of three distinct skeletal layers: a primary laminar layer, secondary blocky layer and a tertiary laminar layer; this arrangement has not previously been recorded in single-walled cyclostomes.