gemmule

Gemmules are dormant, asexual reproductive units produced by many freshwater sponges (Phylum Porifera). The term gemmule derives from the Latin gemma, meaning a bud. Gemmules form during periods of environmental stress such as drought, freezing, or nutrient limitation, enabling survival and rapid recolonization when conditions improve.

Gemmules consist of a compact core of amoeboid cells called archaeocytes, often enriched with nutrient reserves. This core is surrounded by a hardy coat composed of spicules cemented in an organic matrix, sometimes with an additional protective outer layer. The whole structure is resistant to desiccation, freezing, and chemical stress, allowing long-term dormancy in sediments.

When conditions become favorable, gemmules germinate: the protective coat ruptures and the enclosed cells resume growth, migrating to reform the sponge body and its canal system, with the production of choanocytes and other tissues. Dispersal occurs as gemmules are released into the environment and transported by water currents or sediment movement.

Gemmulation is characteristic of many freshwater sponges in the families Spongillidae and related groups; it is less common or absent in most marine sponges. Gemmules contribute to the resilience of freshwater sponge populations in temporary or variable habitats and facilitate recolonization after disturbance.