They are small bud-like cells, which are formed by sponges to withstand unfavourable environmental conditions. A freshwater sponge reproduces both by sexually and asexually. … The internal buds, which are formed by the freshwater sponges are called gemmules.

What are gemmules where and why these are formed?

Gemmules are internal buds formed inside freshwater sponges, e.g. Spongilla. These are formed during unfavourable conditions and help in perennation and dispersal.

Why do some sponges form gemmules?

When conditions deteriorate, such as when temperatures drop, many freshwater species and a few marine ones produce gemmules: “survival pods” of unspecialized cells that remain dormant until conditions improve. They then either form completely new sponges or recolonize the skeletons of their parents.