Formation and Structure of Gemmules

If you have ever been underwater, or have been living near the coasts, or if you have just been a fan of those discovery channels and NGC shows in your childhood, you would have seen these little organisms known as “sponges”. They are multicellular organisms, having pores and channels all over their body, which allow the water to circulate through them.

There are some sorts of buds found internally in these Sponges. These buds are called gemmules. They are basically a comparatively hard-coated cluster of cells which are dormant and embryonic in nature, mostly by freshwater sponges to aid reproduction and development in favorable conditions as well as survival in extreme conditions. Sponges reproduce via asexual reproduction, which means that the process only requires one parent for the birth of an offspring. These gemmules are involved in asexual reproduction via Budding. Each gemmule is capable enough of being developed into a new organism, an adult sponge in its own.
Other than sponges, hydra also reproduces via budding.
Budding can occur either internally or externally. In hydra, the process is external. Various bulb-like growths develop on the body and develop into tiny individuals and detach from the parent body after being fully developed. External budding is supported by the Toxoplasma gondii parasite where two daughter cells produced inside of the mother cell are separated after a certain stage.
Characteristics of gemmules:
Although there isn’t much definition and structure to gemmules, they possess the following characteristics:
  • i. Gemmules are resistant to drying up, they are resistant to desiccation due to weather, temperature, etc.
  • ii. They are resistant to freezing, even in winters during the low temperatures.
  • iii. They are also resistant to anoxia, which means that they can survive even in extreme shortages of oxygen.
  • iv. They can survive and lie around for long period of times, which means that they do not degrade, spoil, or rot.
  • v. Gemmules resemble the endospore of bacteria.
  • vi. They are constituted of amoebocytes.
  • vii. They are surrounded by a thin layer of spicules for support and to deter the predators.
  • viii. These gemmules are super degrading resistant and can survive extreme environmental conditions that could even kill fully grown sponges.
  • ix. The gemmules only resume growing after the environment has become less hostile.

Formation and Structure of Gemmules

Gemmules are formed as a result of the combining of glycoprotein or lipoprotein cells, which are present in the archaeocytes- totipotent cells as a part of the food material, into a cell mass. This cell mass is then surrounded by an amoebocyte, which is a mobile cell. The central mass of the archaeocytes is surrounded by the amoebocytes and a solid thick chitin layer is secreted around it. Sclera oblasts secrete amphidisc spicules in the middle of the internal and external membranes of the cells. This becomes solid and is known as a gemmule.
A finished gemmule is average sized, hard ball-shaped structure. It has the mass of reproductive cells and food material. They are rooted in a thick envelope which is double membrane layered and has amphidisc spicules in between them. These gemmules also have tiny openings on their heads to aid the exit of cells during development and reproduction in favorable conditions.
The outer layers of gemmules also have air chambers which help the sponges in floating.
In short, we can summarise the purpose of gemmules in three points:
  • i. For development and growth
  • ii. To survive unfavorable conditions
  • iii. For reproduction

It should be noted that sponges are found in a huge variety, different shapes, sizes, and colors, and not all sponges reproduce asexually via Gemmulation. Some sponges also reproduce sexually. One family of sponges, namely Clarhizidae, have also been found to be carnivorous, which use spicules for capturing and digesting their prey.

It should also be noted that spicules and gemmules differ greatly and should not be confused together. To clear your doubts, here are some bullet points to remember:
  • i. Spicules form the supporting skeleton in all sponges, whereas gemmules are the reproductive organs of the sponge.
  • ii. Spicules are usually calcareous or silicious in nature, whereas gemmules are embryonic in nature.
  • iii. Spicules pre-exist in the sponges, whereas gemmules develop only during unfavorable conditions.
  • iv. Spicules help aid the secretion of amphidiscs and capturing and digestion of prey (in carnivores), whereas gemmules are meant to aid development and for reproduction.

Spot the Sponges

Sponges are mostly marine, but they can also be found in some freshwater lakes and ponds. To spot the sponges, you can take an underwater dive any time in your nearest pond or lake and chances are that you will find some sponges there. But it is unlikely if the water body is polluted. There are even professional scuba diving lessons and there is great publicity for this thrilling sport. Ponds with beautiful underwater creatures are visited very frequently. Some people like to go inside new water bodies to explore and sometimes grab lucky sights.

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