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

Abstract

The morphologically distinctive Upper Cretaceous (Middle Turonian–Lower Coniacian) hexactinellid sponge Cystispongia bursa (Quenstedt) is redescribed, based on well-preserved near-topotypic new material. Previously included in the Lychniscosa, the taxon is shown to have a hexactinose dictyonal skeleton, necessitating reassignment to the Hexactinosa and, tentatively, to the Porospongiidae. It occurs typically in successions with low net accumulation rates representing comparatively shallow environments and exhibits an exclusively 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 proximal positions. It is restricted to the Northern and Transitional provinces of the English Chalk, and to the Lower Saxony and Subhercynian Cretaceous basins of northern Germany, suggesting latitudinal faunal and palaeogeographic separation from the Münsterland Cretaceous Basin (where it is extremely rare, occurring only at Wüllen) and from the Anglo-Paris Basin, from which it is apparently absent. Its earliest (Mid-Turonian) occurrence coincides with the onset of a cooling phase, expressed in marked oxygen stable isotope perturbations, which is associated with a general shift of boreal faunas to the south. In view of its predominantly northern (Boreal) occurrence and its association with cooler water, Cystispongia bursa has considerable potential in palaeoenvironmental and palaeogeographic interpretations of the Cretaceous in northern Europe.