Some aspects in the life cycle of freshwater sponges (Spongillidae, Porifera) from open Lake Baikal

A histological analysis of the tissue structure in different species of Baikal sponges was performed. The material was collected at a depth of 3–4 m at the Berezovyi test site (southern Lake Baikal) in various seasons of 2001–2003. During the entire year, representatives of the family Lubomirskiidae had a well-developed irrigation system with numerous choanocyte chambers. In Trochospongilla sp. (Spongillidae) from open Baikal, such a tissue pattern was observed only during the summer time. Annually, these sponges undergo tissue regression, i.e., a reduction of the irrigation system accompanied by changes in the cell composition in autumn with subsequent recovery in spring. The onset and termination of tissue regression are adapted to the environment of Lake Baikal.