Asexual Reproduction in Animals > Gemmule Formation

All freshwater sponges like Spongilla and some marine sponges reproduce asexually by the formation of specialised endogenous buds, known as gemmules (internal buds).

Occurrence:

• Seen in sponges.
• Commonly associated with freshwater sponges such as Spongilla.
• Different from Hydra, which reproduces by budding and not by gemmule formation.

Structure of a Gemmule:

A gemmule has the following structural features:

• A central mass of archaeocytes, which are undifferentiated cells capable of forming a new sponge.
• A resistant protective covering around the cell mass.
• In freshwater sponges, the gemmule may have a thick inner chitinous layer and a thin outer membrane.
• In some descriptions, the coat is secreted by amoebocytes around the internal cell mass.

Gemmule in sponges

1. The sponge faces unfavourable environmental conditions, such as drying, thermal stress, or unsuitable conditions.
2. Certain internal cells, mainly archaeocytes, aggregate within the sponge body.
3. A protective layer is formed around this cell mass.
4. The structure develops into a gemmule, which remains dormant and resistant.
5. When favourable water and temperature conditions return, the gemmule germinates.
6. The archaeocytes become active and form a new sponge.

• Freshwater sponges like Spongilla (and some marine sponges) reproduce asexually by forming specialised internal buds called gemmules, unlike Hydra, which reproduces by external budding.
• A gemmule has a central mass of archaeocytes - undifferentiated cells capable of forming a new sponge - surrounded by a resistant protective coat secreted by amoebocytes.
• Under unfavourable conditions such as drying or thermal stress, archaeocytes aggregate within the sponge body, and a protective layer forms around them, developing into a dormant, resistant gemmule.
• When favourable water and temperature conditions return, the gemmule germinates, and its archaeocytes become active, forming a new sponge.