The hexactinellid sponge Cystispongia bursa (Quenstedt 1852) from the Turonian and Lower Coniacian (Upper Cretaceous) of northern Germany and England

The morphologically distinctive Upper Cretaceous (Middle Turonian-Lower Con iacian) hexactinellid sponge Cystispongia bursa (Quenstedt) is redescribed, based on well-preserved near-topotypic new material. Previously included i n the Lychniscosa, the taxon is shown to have a hexactinose dictyonal skele ton, necessitating reassignment to the Hexactinosa and, tentatively, to the Porospongiidae. It occurs typically in successions with low net accumulati on rates representing comparatively shallow environments and exhibits an ex clusively basiphytal attachment to hard substrates. A morphological trend, from pear-shaped with a single central paragaster, to depressed and compact with several additional paragasters, appears to relate to increasingly pro ximal positions. It is restricted to the Northern and Transitional province s of the English Chalk, and to the Lower Saxony and Subhercynian Cretaceous basins of northern Germany, suggesting latitudinal faunal and palaeogeogra phic separation from the Munsterland Cretaceous Basin (where it is extremel y rare, occurring only at Wullen) and from the Anglo-Paris Basin, from whic h it is apparently absent. Its earliest (Mid-Turonian) occurrence coincides with the onset of a cooling phase, expressed in marked oxygen stable isoto pe perturbations, which is associated with a general shift of boreal faunas to the south. In view of its predominantly northern (Boreal) occurrence an d its association with cooler water, Cystispongia bursa has considerable po tential in palaeoenvironmental and palaeogeographic interpretations of the Cretaceous in northern Europe. (C) 2001 Academic Press.