Note
Sponges are one of the oldest metazoangroups, and as such, have contributed a greatdeal to our understanding of life on Earth. Forexample, the discovery of complex immuneand cell aggregation systems in sponges hasled to a better understanding of the cellularprocesses of higher organisms and, in particular,the nature of their cell surfaces as activeagents in cell and tissue recognition (Gamulinet al., 1994).