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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.
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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.
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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.
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11. On the return of favorable conditions the gemmules germinate and give rise to young sponges.
