In this article we will discuss about the spicules and gemmule of sponge.
Spicules of Sponge:
1. The spicules are structures which form the supporting skeleton in sponges.
2. They may be either calcareous or silicious in nature.
3. They may be either monaxon (having one ray) triaxon (having 3 rays) or tetraxon (having 4 rays).
4. Some times they form specialised amphidiscs.
5. They are secreted by special scleroblast cells.
6. Each of them has a central organic axis around which minerals are deposited.
Gemmule of Sponge:
Fig. 96 GEMMULE
1. It is the slide of gemmule of a fresh, water sponge.
2. It is the asexual reproductive body.
3. These bodies develop only in unfavorable conditions.
4. It is actually a round ball-like structure comprising of central mass of archeocyte cells and a thick peripheral layer of amphidiscs.
5. Actually speaking the peripheral layer is made up of an outer membrane, a thick pneumatic layer and an membrane.
6. The pneumatic layer is full of air chambers and help in floating.
7. The central mass communicates to outside by a micrpyle.
8. In addition to archeocytes are also present a few trophocytes and scleroblast cells.
9. The trophocytes are full of food in the form of glyco and lipoproteins.
10. The archeocytes are reproductive cells.
11. On the return of favorable conditions the gemmules germinate and give rise to young sponges.