Gemmules

Gemmules are seed-like capsules formed by sponges for overwintering, containing cells from which a new sponge can grow.

Gemmules have the characteristics that identify sponges to the species level:

With a tube (surrounding the foraminal opening (f) to the exterior of the gemmule) extending from the gemmule surface

Heteromeyenia tentasperma Heteromeyenia tubisperma
With no tube extending from the gemmule surface (though may have a short collar)
- Gemmoscleres embedded radially and extending beyond the surface
  
  Anheteromeyenia argyrosperma Ephydatia fluviatilis Ephydatia muelleri Heteromeyenia baileyi
- Gemmoscleres tangential to the surface
  
  Eunapius fragilis Duosclera mackayi
- Gemmoscleres embedded radially and barely visible at the surface
  
  Racekiela ryderi Corvomeyenia everetti Radiospongilla crateriformis Trochospongilla pennsylvanica
Species with two different kinds of gemmules, one lacking gemmoscleres

Spongilla lacustris Spongilla lacustris

Milwaukee Public Museum