A new type of central cell in the choanocyte chambers of Pellina fistulosa (Porifera, Demospongiae)

Central cells of a hitherto unknown type, forming a continuous, perforated layer at the level of the distal collar ends in each choanocyte chamber, have been found in the choanocyte chambers of Pellina fistulosa. The collars project through the pores of the perforated central cell layer. The spaces between the collar ends and between the collars and the cone cell ring in the apopyle region are sealed by the central cell cytoplasm. The latter represents an impermeable barrier for particulate material as well as for water and thus enhances the filtration efficiency by preventing a bypass of water and particles between the collar apices.