A yellow–green algal symbiont in the freshwater 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 Eustigmatophyceae in the division Heterokontophyta.
3. The relationship of the alga with C. everetti appears to be specific and it contributes significantly to the energy budget of the host.
4. Although the growth form of C. everetti is very similar to other freshwater sponges that usually have green-algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and sponges in the development of symbiotic associations in fresh water.