Gemmule – Formation, Structure and Role in Sponge Reproduction

Gemmules are the asexual reproductive structures found in some freshwater and marine sponge species. The gemmules in sponges are produced in adverse weather circumstances, including drought or low temperatures. The gemmules play a role in giving sponges the ability to tolerate harsh environmental conditions. In this article, we will study the gemmules in sponges, their structure, characteristics, and their advantages.

What are Gemmules?

Definition of Gemmule: A gemmule is an asexually formed clump of cells that can differentiate into an adult freshwater sponge. These are tiny, bud-like clusters of cells that sponges generate to survive harsh environmental conditions.

“Gemmule” is a term coined by Charles Darwin in his theory of pangenesis, proposed in the late 19th century. According to this theory, gemmules were hypothetical particles that were believed to be produced by all cells. They were responsible for transmitting hereditary information from one generation to the next.

In Darwin’s concept of pangenesis, gemmules were thought to circulate throughout an organism’s body, accumulating in the reproductive organs and ultimately being passed on to offspring during reproduction. These gemmules were believed to carry information from various parts of the body and were responsible for determining the traits of the offspring.

Structure of Gemmules

The micropyle, spicule, inner layer, archaeocytes, and outer pneumatic layer comprise the structure of gemmules. A brief about the structure of gemmules in sponges is given below:

• Gemmules are typically small, rounded structures surrounded by a tough, protective layer called the scleroprotein coat.
• Inside the scleroprotein coat, gemmules contain a mass of undifferentiated cells known as archaeocytes.
• Throughout the mass of archaeocytes, small calcium carbonate spicules are scattered. They provide structural support to the gemmule.
• Gemmules also contain lipid droplets and glycogen granules, which serve as energy reserves to sustain the dormant cells during adverse conditions.
• Some gemmules may possess internal canals that facilitate the exchange of gases and nutrients, aiding in the survival of the enclosed cells.

Gemmule Diagram

The following is a labeled diagram of gemmule of sponge:

Gemmule of Sponge Diagram

Parts of Gemmule

There are four major parts of gemmule:

1. Scleroprotein coat
2. Archaeocytes
3. Glycoprotein Granules
4. Inner Canals

Gemmules Classification

Gemmules classification is based on different criteria:

Gemmule Classification Based on Structure

• Simple Gemmules: Gemmules that have a basic structure consisting of a protective coat surrounding a mass of cells and possibly spicules.
• Complex Gemmules: Gemmules with additional structural features such as internal canals or specialized layers.

Gemmule Classification Based on Composition

• Calcified Gemmules: Gemmules containing calcium carbonate spicules embedded within their structure.
• Non-Calcified Gemmules: Gemmules lacking calcium carbonate spicules.

Gemmule Classification Based on Ecological Function

• Asexual Reproductive Gemmules: These gemmules primarily serve as a means of asexual reproduction and allow sponges to propagate and survive adverse environmental conditions.
• Survival Structures: These gemmules function as survival structures and enable sponges to endure harsh conditions such as drought or extreme temperatures.

What are the Characteristics of Gemmules?

Gemmules lack a lot of structure and definition, but they have the following qualities:

• Gemmules are highly resistent structures that can withstand extreme conditions like dessications, freezing, etc.
• They may also survive severe oxygen shortages.
• Gemmules resemble bacterial endospores and usuasly act as survival structures
• They are spherical and lie in cluster.
• They are capable of floating and have a peumatic layer that provide buoancy.
• They are composed of germinative cells called archaeocytes .
• A thin coating of spicules covers them, providing support and discouraging predators.

What is the Process of Gemmule Formation?

The aggregation of amoeboid cell within the sponge causes gemmule production. As these cells proliferate, a hard, protective coating made of collagen and spicules surrounds them. The cells within the protective layer undergo specialised differentiation, giving rise to cell types such as archaeocytes, which are totipotent.

Gemmules can germinate, and the cells within can differentiate and grow into new sponge creatures when the conditions are right again. This allows the sponge to reproduce asexually and colonise new places. A motile cell called an amoebocyte circulates the core of the archaeocytes and begins to secrete a thick layer of solid chitin surrounding them.

Scleraoblasts located between the internal and external membranes secrete amphidisc spicules. A mature gemmule is a round, solid structure containing reproductive cells rich in nutrients. It is surrounded by a dense double membrane encased with amphidisc spicules.

Under optimal growth conditions, cells emerge through a tiny aperture known as the Micropyle. Freshwater sponges die in the autumn, leaving behind a large number of gemmules. Amid both the summer and the winter, these gemmules continue to function. When there’s a lot of water, the gemmules begin to grow into new sponges.

Gemmule Formation Examples

Gemmule formation is a method of asexual reproduction used by certain organisms like:

• Freshwater sponges (Porifera)
• Marine sponges, bryozoans (moss animals)
• Hydras (Cnidaria)
• Planarians (Platyhelminthes)

Role of Gemmule in Sponge Reproduction

Gemmules serve as vital reproductive structures in certain freshwater sponges, offering a means of asexual reproduction and survival in challenging environmental conditions. These structures are formed by sponge organisms as a response to adverse factors such as drought, low temperatures, or other stresses. Gemmules have protective covering of scleroprotein that protect the archaeocytes or generative cell during the stressful conditions and when favourable conditions return, these gemmules allow archaeocytes to germinate and mature into new sponges.

Advantages of Gemmule Formation

The advantages of gemmule are as follows:

• Resistant to unvavourable condition: Gemmules are highly resistant to severe environmental stresses like dessication and freezing.
• Escaping long term environmental adversities: Gemmules being highly resistant can survive long periods of environmental adversities and hence ensures the survival of the species even after long periods of unfavourable conditions.
• Asexual reproduction: Gemmule formation is a method of asexual reproduction and also an energy efficient reproductive mechanisms.
• Colonization of new environment: Gemmules can easily float in water due to the presence of air chambers and a thick pneumatic layer. Hence they can migrate to new areas and colonize easily.

Conclusion: Gemmule – Structure formation and Sponge reproduction

In conclusion, gemmules are reproductive structures used by certain freshwater sponges to ensure survival and propagate in challenging environments. These structures are surrounded in a protective scleroprotein coat that protects reproductive cells during adverse conditions, allowing them to germinate and develop into new sponges when favorable conditions return. Gemmule formation serves as a vital mechanism for asexual reproduction, resilience to environmental stresses, and colonization of new habitats, highlighting their significance in the life cycle.

FAQs on Gemmule – Structure formation and Sponge Reproduction

What is a Gemmule?

A gemmule is a reproductive structure in some freshwater sponges, enabling asexual reproduction and survival in harsh environments by protecting and germinating reproductive cells.

Explain the Process of Formation of a Sponge.

When cells aggregate and differentiate during the larval stage, a sponge is formed. Eventually, these cells arrange themselves into the distinctive sponge body structure.

Name Different Methods through Which a Sponge can Reproduce.

Sponge reproduction is asexual as well as sexual. Usually, sperm and eggs are released into the water for external fertilisation during sexual reproduction.

Explain the Structure of Gemmules.

The Micropyle, Spicule, Inner Layer, Archaeocytes, and Outer Pneumatic Layer comprise the structure of Gemmules.

Where are Gemmules Found?

Gemmules often have a spherical or ball-like shape with a thick covering of siliceous spicules on the periphery and a core mass of amoeboid cells.

What is the Process of Gemmulation?

Gemmulation is the process of gemmule formation in sponges. During this process specialized cells aggregate within a sponge, forming a mass enclosed by a protective scleroprotein membrane that together forms the geemule.

What is the Difference Between Budding and Gemmule Formation?

Budding is a form of asexual reproduction where a new organism develops as an outgrowth from the parent organism. Whereas, Gemmule formation involves formation of cell aggregates encased in a protective covering.