Excavation patterns and spiculae dimensions of the boring sponge Cliona celata from the SW Netherlands

Actuopaleontological aspects of Cliona celata from the Dutch Delta Region were investigated. This tunneling sponge occurs abundantly in limestone boulders and in shells of Ostrea edulis, Crassostrea gigas and Crepidula forricata. Ostial and oscular papillae protrude from the substratum surface through perforations. All found spicules are tylostyles. Thè length of the tylostyles prepared from ostialpapillae is positively correlated with the diameter of the perforations which contain these papillae. The tylostyle diameter is not correlated with the perloration size. Reproduction apparently is mainly asexual. Excavation patterns in the substrata are described. Mathematical models of percolation rates and patterns are applied to describe the relative age of sponge parts in oyster shells. Interactions of sponge tunneling with borings of two polychaete worms, Polydora aliata and P. hoplura, are studied. In the Dutch Delta Regiononly the (x- and the j3-stage of Clt'ona celata are found. Therefore the y-stage was collected near Roscoff, France, to measure tylostyle length and papillae distribution.