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
- With no tube extending from the gemmule surface (though may have a short collar)
- Species with two different kinds of gemmules, one lacking gemmoscleres