Sedimentary inclusions in the deep-water sponge Geodia barretti (Geodiidae, Demospongiae) from the Korsfjord, western Norway

Abstract

In various specimens of the deep-water sponge Geodia barretti, inclusions consisting of siliciclastic sediment were found, with spicules of G. barretti as main clasts. The inclusions were clearly separated from the surrounding tissue by a cortex of microscleres. Some were entirely surrounded by sponge tissue, while others were connected to the sponge surface. Lipid biomarker analysis showed significant differences between inclusions and the choanosome, indicating that the inclusions are separate bodies within the sponge tissue. Microscopic examination showed that the cortex surrounding the inclusions had been generated in choanosomal tissue. We discuss possible hypotheses of the genesis of these structures, and conclude that they are most probably the remnants of surface injuries caused by predators, which have subsequently been filled with sedimenting particles. To protect the injured tissue from fouling, the sponge reacted with complex healing processes: a tissue barrier was created, new spicules were produced in the choanosome and a new cortex was generated. Encapsulation diminished contact of the injured surface with the water and prevented further accumulation of foreign material. It remains an open question how these complex immune response mechanisms are co-ordinated in the sponge tissue.