Article: Secondary nanozooecia in some Upper Palaeozoic fenestrate Bryozoa

Autozooecial apertures sealed by perforate terminal diaphragms have been found in eleven species of British and Irish Carboniferous and Permian fenestrate Bryozoa. In their skeletal morphology, intra-colonial abundance, and distribution they resemble the perforate terminal diaphragms of polymorphs that are termed secondary nanozooecia in the Recent tubuloporinid cyclostome Plagioecia and the lichenoporid cyclostome Disporella. The former presence in fenestrates of single-tentacled non-feeding polymorphs comparable to those of Plagioecia and Disporella is inferred. As in Plagioecia and Disporella, secondary nanozooecia of fenestrate bryozoans may represent a late stage of zooidal ontogeny. The function of secondary nanozooecia in Plagioecia and Disporella is unknown, but those of fenestrates possibly had a defensive/cleaning function comparable to that suggested for primary nanozooids in the Recent tubuloporinid cyclostome Diplosolen obelium.