Asexual Reproduction
| Budding | Number of individuals in colonies increases, or new colonies are formed. Archaeocytes collect at the surface and Pinacoderm bulges out to receive them. Bud grows into an adult individual. Either remains attached to the parent individual or gets detached and attached nearby to develop into an independent colony. |
| Fission | Throw off parts of their body which develop into individual sponges. New individual forms a new colony. |
| Reduction Bodies | Freshwater and Marine sponges disintegrate in adverse conditions into reduction bodies. Each body consists of an internal mass of Amoebocytes, covered externally by a pinacoderm layer. When favourable conditions return, these reduction bodies grow into complete new sponges. |
| Gemmules | Internal buds that eventually detach and develop into new individuals. Enable the sponges to tide over unfavourable conditions, like excessive cold and draught. Gemmule is a small hard ball with an internal mass of archaeocytes, surrounded by a resistant chitinous covering made of two membranes. Protective envelope may be strengthened by siliceous amphidisc spicules. |
Sexual Reproduction
Most sponges are monoecious, but dioecious sponges are also known.
Sperms and Ova are derived from Archaeocytes or Choanocytes, which undergo Gametogenesis.
Even in hermaphrodites, cross fertilisation occurs because eggs and sperms are produced at different times.
Fertilisation:
Sperms are released to the outside through outflowing water and make their way to another sperm through the ingressing current.
Choanocytes transfer sperms to the mature ova, which lie in flagellated Choanoderm.
Fertilisation is in situ.
Development:
Early development within the maternal sponge, leading to development of a larval stage.
Amphiblastula: Hollow, oval, larval stage. Calcareous sponges. Anterior half of amphiblastula bear flagella, posterior half does not.
Parenchymula: Solid, oval or flattened larval stage. Calcarea, hexactinellida, Desmospongiae.
Entire outer surface bears cilia.
Regeneration
Individual pieces of Sponge, no matter how small, will grow into a complete sponge if it has Amoebocytes and Choanocytes.
Calcium and Magnesium ions play a role in regeneration.
Bergquist: If a tissue is grafted in a sponge from another sponge of same species, the host and graft will grow together. If the graft is from a different species, the host will reject the graft.