Preparation and karyotype analysis of mitotic chromosomes of the freshwater sponge Spongilla lacustris.

The present study documents for the first time the karyotype and mitotic chromosomes of a sponge. For the studies the freshwater sponge Spongilla lacustris (Lin. 1758) was used. Its karyotype comprises nine different chromosome pairs ranging in size from 2.1 to < or = 0.7 microns. Changes in size and shape of the chromosomes during the progression of mitosis are documented both light and electron microscopically. The data reveal that the lowest multicellular eukaryotes, the sponges, have already reached a high level of evolution of the mitotic mechanism.