A YELLOW-GREEN ALGAL SYMBIONT IN THE FRESH-WATER SPONGE, CORVOMEYENIA-EVERETTI - CONVERGENT EVOLUTION OF SYMBIOTIC ASSOCIATIONS

1. A previously undescribed symbiotic relationship is reported between the freshwater sponge Corvomeyenia everetti, which occurs throughout eastern North America, and a yellow-green alga. 2. Ultrastructural and pigment analyses place the algal endosymbiont within the class Eustig matophyceae in the division Heterokontophyta. 3. The relationship of t he alga with C. everetti appears to be specific and it contributes sig nificantly to the energy budget of the host. 4. Although the growth fo rm of C. everetti is very similar to other freshwater sponges that usu ally have green-algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and spo nges in the development of symbiotic associations in fresh water.