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Hexactinellid

life science Maturity 5-7 Next article →

Hexactinellid sponges, commonly known as glass sponges, are unique marine animals.

Euplectella 01
Euplectella 01

They are defined by skeletons made of siliceous spicules. These are tiny, glass-like structures with four or six points. These spicules fuse together to create a sturdy lattice. This lattice provides a structural frame for the animal. Most scientists classify them within the phylum Porifera. However, some researchers believe they are distinct enough to belong to their own phylum, Symplasma. These organisms are vital to deep-sea ecosystems. They help manage nutrient cycles and provide habitats for other life.

The biological structure of a glass sponge is very different from other animals.

Most of their body is composed of syncytial tissue. A syncytium is a continuous mass of cytoplasm containing many nuclei. Instead of having many separate cells, the sponge acts like one large, connected web. This web is held in place by a scaffolding of silica spicules. To move nutrients, the sponge uses cytoplasmic bridges. These bridges act like rivers to transport organelles and nuclei. These bridges are controlled by plugged junctions. These junctions allow certain substances to pass while blocking others. This unique physiology allows for a high flow of ions. Because of this, electrical signals can move rapidly through the organism.

Feeding and water movement follow a specific mechanical process. The sponge body consists of three main parts. These are the inner peripheral trabecular network, the outer peripheral trabecular network, and the choanosome. The choanosome serves as the sponge's mouth. Water enters the sponge through small perforations in bell-shaped chambers called choanosyncytia. Inside these chambers, tiny structures called collar bodies use flagella to create motion. The beating flagella suck water through the sponge's internal passages. This movement carries food into the choanosome. The sponge then expels the water through the open ends of the chambers. Unlike many other sponges, hexactinellids cannot contract their bodies.

These sponges have developed advanced ways to sense their environment.

Venus Flower Basket
Venus Flower Basket

They use electrical neuron signaling to respond to external stimuli. For example, the species Rhabdocalyptus dawsoni can detect sediment in the water. When it senses too much sediment, an electrical signal travels through the body. This signal tells the organism to stop its feeding process. Different species have different thresholds for these signals. They can endure a certain amount of stimuli before they react. This rapid communication is possible because about 75% of the sponge tissue is fused in this syncytial way.

Glass sponges are famous for their incredible longevity.

Glass-sponge, Euplectella aspergillum
Glass-sponge, Euplectella aspergillum

Some experts believe they might be the longest-lived animals on Earth. Scientists have tentatively estimated a maximum age of up to 15,000 years. One specific model of the species Scolymastra joubini suggested an age of 23,000 years. However, researchers adjusted this estimate due to historical changes in sea levels. They now believe the maximum age is closer to 15,000 years. For a sponge that grows to 1 meter in length, life expectancy is estimated at 200 years. Most sponges average a maximum growth of about 32 centimeters.

These animals create massive underwater structures known as sponge reefs.

Venus Flower Basket
Venus Flower Basket

In places like British Columbia, Washington, and Southeast Alaska, they form large bioherms. Some species, such as Sarostegia oculata, host symbiotic zoanthids. These tiny animals cause the sponge to look and act like a coral reef. Before recent discoveries, scientists thought sponge reefs had died out during the Jurassic period. However, reefs in the Hecate Strait have been found to grow very high. These reefs are important habitats for many marine species. They also show how sponges can thrive in diverse environments.

While many live in the deep sea, they face modern environmental threats.

Glass-sponge, Euplectella aspergillum
Glass-sponge, Euplectella aspergillum

Most hexactinellids live in deep waters away from most human activity. However, shallow-water reefs are more vulnerable. Research on the species Aphrocallistes vastus shows that climate change is a risk. Increasing water temperatures and acidification can weaken the sponge's skeleton. This makes the glass structure less stiff and strong. To protect them, the Canadian government created a Marine Protected Area. This area covers parts of the Hecate Strait and Queen Charlotte Sound. These regulations prohibit bottom-contact fishing to keep the reefs safe.

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🖼️ Images & Media (4)
File:Bolosoma stalked glass sponge (39506105791).jpg
Bolosoma stalked glass sponge (39506105791).jpg
File:Euplectella 01.png
Euplectella 01.png
File:Venus Flower Basket.jpg
Venus Flower Basket.jpg
File:Glass-sponge, Euplectella aspergillum.jpg
Glass-sponge, Euplectella aspergillum.jpg
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