The Invertebrate: What are Sponges? What are Glass Sponges (Hexactinellids)?

Demosponges

What is a marine Sponge?

Sponge is a simple word used to discuss these animals. Sponges are known by scientists as Porifera. In Latin, this means "pore-bearing." The pores, or tiny holes, in the skin of a sponge water in so that the sponge can extract oxygen and food for all of its cells to stay alive. The water passes by the mesohyl, also called the mesenchyme which contains cells and the sclerocytes. Sclerocytes make spicules. After the water is filtered, it is pushed out of the sponge. First it goes to a hollow area called the spongocoel, which is a large, empty cavity. Sponges contain one large hole at the top of their bodies, known as an osculum, and they also have smaller holes on the sides known as ostia. With so much water flowing in and out of a sponge every day, sponges in the Caribbean Sea can filter the entire sea in just one day. That's pretty impressive for an animal that was thought to be a plant until the year 1765!!!

Scientists believe that sponges were the first animals to be alive. The ancestors of today's sponges were alive billions of years ago. Sponges have looked the same for millions of years. They are the most simple of all animals, with no brain or organs, but they have been helping mankind and nature for as long as they have been on the planet.

Sponges may seem to be plants, but they are really just primitve, simple animals. They are not animals like humans because they only have cells. Cells are the tiniest parts of the body, and you can't even see them. Each cell in a sponge has a special job, and when cells of the same type come together, they make tissues. Tissues create organs, but sponges don't have any organs. That means no brain, eyes, hearts, etc. However, despite all that is set against them, they always manage to stick together. While their spicules, tiny needles that stick out from the sponge, hold them together, sponges also have another special way to stick together. If you had a sponge in a salt-water aquarium and break it up into thousands of pieces, the cells would come back together again in the exact same shape within several hours.

In 2008, Gordon Love of the University of California Riverside discovered fossil traces in an oil field on the Arabian Peninsula. They became the oldest evidence yet of animals, pushing back the known origins of higher life to more than 635 million years ago. They were unearthed in Oman and reveals that tiny sea sponges were abundant 635 million years ago, long before most of the planet's other major animal groups evolved, according to a new analysis.

Love’s team identified the fossils while analyzing sedimentary deposits mined by Oman’s national oil company. The sediments date to the last stages of the the aptly-named Cryogenian period after a deep freeze.

What life may have looked like in the Ediacaran Sea

This early life hardly looked like us, but some of the so-called demosponges can be sizable today. Demosponges still make up 90 percent of all sponges on Earth and 100 percent of Earth's largest sponges, including barrel sponges, which can be larger than an old-style phone booth.

The ancient demosponges — probably measuring across no more than the width of a fork tine — were pinned down via fossilized steroids, called steranes, which are characteristic of the cell membranes of the sponges, rather than via direct fossils of the sponges themselves.

Class Hexactinellida (Glass Sponges)These are deep-sea sponges. They lack an epidermal covering, and their skeletons are composed of spicules of silica. The spicules, which often form a latticework, have six points or some multiple thereof. Many hexactinellids are called "glass sponges." Hexactinellids were the first group of sponges to develop, but as said before, many scientists do not believe that they are sponges at all. Oddly enough, they have electric receivers on their spicules which can conduct electricity!

Body plan with lattice of spicules, flagella in chambers of pores

Glass sponges are pale in color and are cup- or basket-shaped. The spongocoel is large, and the osculum is covered by a grillwork of fused spicules. When the living tissue is removed, the cylindrical skeletons often have the appearance of spun glass. The glass sponge known as Venus's-flower-basket (Euplectella) supplies a home for certain shrimps that become trapped by the lattice of spicules. The body plan of Hexactinellida is between syconoid and leuconoid. Glass sponges are different from other sponges in a variety of other ways. For example, most of the cytoplasm is not divided into separate cells by walls but forms a syncytium or continuous mass of cytoplasm with many nuclei (e.g., Reiswig and Mackie, 1983). Like almost all sponges, the hexactinellids draw water in through a series of small pores by the whip like beating of a series of hairs or flagella in chambers which in this group line the sponge wall.

The Venus's Flower Basket

Hexactinellids are, typically, limited to the deep sea with the result that few people have seen them or studied them. An exception may be the “Venus’s Flower Basket” A pair of shrimp remain protected together inside. The sponge together with the imprisoned pair of shrimp is often given as a gift at weddings in Japan and the Philippines to signify a long relationship.

Reef-building glass sponges were once thought to have been extinct for 100 million years. But a new live cluster of the organisms has been discovered off the west coast of the US - only the second known to exist.

Furthermore, unlike the other known glass sponge reefs in Canada, the US reefs appear to be fuelled by methane. Paul Johnson, of the University of Washington, US, led the expedition that discovered the reefs on 10 June off the coast of Washington state. He says they are oases of marine life, several hundred feet across, and surrounded by uninhabited expanses of seafloor.

Glass Sponge Reef location

Glass sponge reefs were common during the “Age of Dinosaurs”, but were unknown since that time. Some were being destroyed by trawling. They have recently been designated as no trawling areas by Fisheries and Oceans Canada; but full Marine Protected Area status is needed to ensure that they remain intact. Glass sponges occur mainly on muddy sea bottoms at great depths and due to their delicate nature are broken and shattered whenever there is trawling along the muddy bottom.

Sponges may seem to be plants, but they are really just primitive, simple animals. They are not animals like humans because they only have cells. Cells are the tiniest parts of the body, and you can't even see them. Each cell in a sponge has a special job, and when cells of the same type come together, they make tissues. Tissues create organs, but sponges don't have any organs. That means no brain, eyes, hearts, etc. However, despite all that is set against them, they always manage to stick together. While their spicules, tiny needles that stick out from the sponge, hold them together, sponges also have another special way to stick together. If you had a sponge in a salt-water aquarium and break it up into thousands of pieces, the cells would come back together again in the exact same shape within several hours.

How A Sponge Takes In Food
The diet of sponges consist of bacteria and other organic matter. Some sponges feed on green algae, dinoflagellates, and cyanobacteria. To get the bacteria and other organic matter, water flows through the pores and provides the sponge with its food. They are known as “suspension feeders” and collect nutrients from the water through their choanocyte cells. About 90% of the bacteria in the water that flows through them (which is pushed through with the help of beating flagella) is absorbed as nutrients. The choanocyte cells consist of a flagella surrounded by a collar cell. As the choanocyte cells uptake the food, the flagella (a cellular 'tail' that aids in motion) creates a water current and the collar cells ingest the food. The choanocytes take up the nutrients through phagocytosis. Phagocytosis is the uptaking of large food particles. Sponges also consist of amoebocytes, which along with discarding of foreign bodies also are responsible for uptaking nutrients from the water and from choanocyte cells. Once amoebocytes uptake the nutrients, they digest these nutrients and then transport the nutrients to other cells.

• Porocytes- doughtnut-shaped cells that align the body wall.
• Choanocytes- flagellated cells that aid in circulation, water movement, and digestion.
• Amoebocytes- cells that are important in getting rid of foreign bodies.
• Mesohyl- a part of the sponge that separates the two layers of the sponge.
• Spongocoel- the mid- cavity (compartment) of the sponge.
• Osculum- larger openings within the sponge where water is passed through. (More complex sponges have more osculum)
• Epidermis- tightly packed cells aligning the sponge.
Spicules- makes up the skeleton of the organism, they provide the support need to keep the pores open. Spicules are made of calcium carbonate and silica, or the organic substance spongin.

How Do Sponges Reproduce?

Sponges are hermaphrodites, which means that they have male and female reproductive parts. Sponges also produce female and male gametes (sperm and egg). Egg and sperm arise from the choanocyte and amoebocyte cells of the sponge. The eggs of sponges are housed in the mesohyl. The sperm is carried out through the water current that circulates the sponge. Sperm are created, concentrated and sent out the excurrent openings, sometimes in masses so dense that the sponges appear to be smoking. The temperature of the water that the sponges live in usually determine when the sponges release the sperm. These sperm are then captured by female sponges of the same species. When the sperm enters a collar cell of a neighboring sponge, the collar cell loses its collar, transforming the cell into a specialized cell that brings the sperm to the eggs. Fertilization (the combination of egg and sperm) occurs in the mesohyl of the sponge. Sponges can also reproduce asexually (by not having sex) as pieces of the sponge break off and are then repaired. Some species will make internal buds, called gemmules, that can survive in extreme conditions which the rest of the sponge cannot survive in. Some sponges reproduce asexually.