gemmulesdormant

Gemmules are dormant, asexual reproductive structures produced by freshwater sponges and some marine sponges. They are essentially packages of cells resistant to unfavorable conditions such as drying out, freezing, and lack of oxygen. A gemmule consists of a mass of amoeboid cells called archaeocytes, enclosed within a protective shell. This shell is typically made of two layers, an inner protein layer and an outer spongin layer, which can be further reinforced with spicules, needle-like structures made of silica or calcium carbonate. The composition and arrangement of these spicules are often species-specific and are used in sponge taxonomy.

When environmental conditions become favorable, usually with increased temperature and availability of water, the gemmule hatches. Water enters through a small pore called the micropyle, activating the archaeocytes. These cells then proliferate and differentiate, eventually forming a new sponge. Gemmules can survive for extended periods, allowing sponges to persist through harsh seasons or periods of drought. They are a crucial adaptation for freshwater sponges, which inhabit environments prone to significant fluctuations. The dispersal of gemmules can occur through various means, including water currents, being carried by animals, or through the fragmentation of the parent sponge.