Silica Sponge

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Classification/Diagnostic Characteristics

The Silica sponge is one of 5,000 living species of sponges. A sponge is essentially a water-filtering system. It does not move and all species must feed on food particles suspended in the water. All sponges have a canal system, through which they pump water (1). Silica sponges are poriferans that stand among one of the oldest animal fossils dating back to the Late Precambrian Era (roughly 4600 to 500 million years ago). There are two classes of silica sponges under the proifera phylum: Hexactinellida and Demospongiae (1). While the structure and color varies for these organisms, those from both classes can be distinguished by their spicules (the exterior building blocks for sponges) made of silicon dioxide. The diagnostic characteristics for this organism include but is not limited to: acquiring and digesting food, self protection, maintaining homeostasis, sensing the environment, and locomotion to a limited extent.

Silica sponges are usually cylindrical, with a thin integument and a large opening (atrium) inside. They can resemble vases. The body is completely made of silica formed into 6-pointed spicules, which are extremely small formations that give the sponge structure and weave together to give the sponge a strengthened structure. The sponge is anchored to its surface by fibers which have similar properties to the fiber optic cables used in a variety of modern technologies. The fibers have the ability to receive and transmit light, and are speculated to be meant to attract other aquatic creatures. The color of the actual sponge depends on the amount of particle matter they have in their tissues. (SS-7)

Relationship to Humans

While the silica sponge and the human are phylogenetically distant, both organisms share: a carbon composition, specialized cells for performing different functions and the capacity to reproduce sexually, or with different organisms of the same species.

Scientists are currently trying to figure out the process by which silica sponges produce their silica skeleton. They believe that this process could make industrial production of silica cheaper and more efficient. (JM 15)

Researchers also hope to use the silicon structures found in the sponges in biomedical approaches. Studies have shown that silicon deprivation can lead to severe skeletal malformations, which leads to the belief that silicon promotes bone formation, a belief which was shown to be true when cell cultures revealed increased mineralization in the presence of silicon. Bio-engineers hope to use this knowledge gained from the sponges to create protective biosilica layers on teeth, or to regenerate lost bone tissue.(SF)(16)

Habitat and Niche

They are ubiquitous benthic creatures (meaning that they are found at the bottom of water bodies) and largely immobile. The silica sponge has no specific structures to catch or break down food so they filter feed using outer pores in their body.
Sponges are found in all marine and many freshwater habitats. Located in rivers, streams, rock pools, frozen arctic seas, and warm tropical seas, sponges can thrive in nearly any body of water (3). (SP)

Predator Avoidance

Silica sponges are sessile, or immobile, and have no behavioral mechanisms to avoid predators. They can however present themselves as unappetizing with their tough tissue network which causes them to be indigestible.

Because sponges are sessile, they have developed ways to protect themselves from predators. Microbial pathogens that have the potential to harm sponges if they are able to grow on their surfaces or within the sponge cells are controlled by sponges with powerful chemicals that are antibiotic, cytotoxic, toxic to cells, and feeding-deterrent. The storage and secretion of these toxic chemicals allows sponges to ward off potential predators as well as pathogens that could settle on their bodies. In addition, when predators attack, sponges have the ability to recognize tissue wounds and in turn convert stored chemicals into highly toxic agents only locally at the wound to attack the predator and prevent further damage. (8) (CM)

Nutrient Acquisition

By utilizing flagellum on the surface of external chambers connected by canals, the silica sponge can create a unidirectional flow of water. Through this process, cells in the outside sponge walls can filter and circulate nutrient particles and excess water throughout the rest of the organism. Individual cells can attain these particles through a process known as phagocytosis in which the exterior of the cell literally engulfs the targeted particles for internal consumption. Interestingly, the individual cells in sponges such as these are relatively independent when compared to other developed species today.

The sponge filters particles that it absorbs from the water around it by size. Small particles, from 0.5 to 50 microns in diameter, are captured by the sponge's ostia, or the holes on its surface, where they are processed by pinacocytes. Particles larger than 50 microns, which cannot fit into the ostia, are consumed by pinacocytes near the surface through phagocytosis. Particles smaller than 0.5 microns, including most microorganisms that constitute the sponge's diet, travel through the ostia and are consumed by choanocytes. Transport cells known as archeaoctyes ferry packaged food from digestive cells to non-digestive ones, spreading nutrients throughout the sponge. (YR) (11) (12)

Reproduction and Life Cycle

Similar to many other poriferan, the silica sponge reproduces both sexually and asexually, or without the necessity of other organisms. Furthermore, this sponge is hermaphroditic and thus produce eggs (female reproductive cells) and sperm (male reproductive cells) at different times.The silica sponge reproduces sexually in that sperm is manufactured and released by male cells of the sponge (through a water medium) only to be received by female sponges of the same species. Fertilized cells are then developed into ciliated larvae inside an area called the mesenchyme. Most poriferan can also reproduce asexually by the process of budding, the outgrowth of an organism with the addition of similar but new cells, and regeneration, the repairing of damaged components.

Initially, poriferan are ciliated larvae that are capable of swimming freely in water. As they mature, they become sessile, or immobile, and latch themselves onto a surface.

Growth and Development

The silica sponge develops asexually by manufacturing and compiling very similar cells in a process known as budding. Once sponges become excessively large, water pressure derived from waves or current can displace fragments of the sponge to other locations. Using a variety of external cells, this detached sponge can latch onto new surfaces and establish itself as a distinct organism.
sponge development.png
(SL 4)


Similar to other sponges, the silica sponge is not distinguished by unique layers of tissue. Instead, there is a single layer of tough, tissue (that is uniform throughout the organism) to protect against predators. The silica sponge consists of a silicon based skeleton as opposed to a traditionally carbon based skeleton.

The epithelium of most sponges is called the pinacocyte. The pinacocyte is a type of flattened cell which is able to contract and expand, influencing the ability of the sponge to react to a disturbing outside force. (AC) (20)


The silica sponge is fundamentally sessile and is unable to physically move to fulfill its needs. As a result, it utilizes its pores to carry out basic bodily functions. Interestingly, it is able to move freely during its larvae stage.

Adult sponges are not capable of moving from location to location; however, they can move parts of themselves. For example, sponges can open or close incurrent pores depending on the porocytes and the nutrient levels around itself. In addition, sponges can contract due to pinacocytes, which are flat cells that lie on the outside of sponges. Desmacytes, which are connective tissue cells, can also contract in the sponge. (17) (RS)
Sponge Diagram (18) (RS)

Sensing the Environment

The silica sponge is able to adapt to its environment in a variety of ways. First, it orients itself perpendicular to the water current to allow for maximum nutrient absorption.

Certain sponge species are adapted to freshwater environments, as their skeletons allow them to live in either hard or soft sediments. Pores allow them to filter the water for food and other nutrients. Inside the body there are flagella that create currents so their outer cells filter food.
Sponges have strong structures that are able to handle the high volume of water that flows through them each day. By constricting their openings, sponges are able to control the amount of water that flows through them. (19) (NU)

Gas Exchange

Using their pores and a centralized internal water system, individual cells can exchange gases and fluid with the outside environment due to diffusion (and osmosis). Silica sponges maintain a very high surface to volume ratio due to their structure which allows them to exchange gas efficiently (SL).

All over the sponge are small pores, called ostia. Ostia draw water into them, and circulate it throughout its body by the action of cells called choanocytes. These choanocyte cells contain whiplike structures called flagella, that move around and push water through the sponge. As water is drawn in and then and out of the sponge, food and oxygen are brought to the sponge and waste and carbon dioxide removed. (SM) [

Waste Removal

Similar to the gas exchange mechanisms, individual cells can release waste with the outside environment due to diffusion and exocytosis.

Silica sponges have collar cells that beat their flagella back and forth to force water through the sponge. The water takes carbon dioxide, the organism's waste, out of the cell. (13) (LK)

Environmental Physiology (temperature, water and salt regulation)

Poriferans can live in both fresh water and salt water environments. Water is controlled by constricting or relaxing the external pores. Temperature is controlled by limiting the flow of of water to conserve heat and increasing the flow of water to release heat. Salt regulation is maintianed by diffusion with the internal water canals or the outside environment when possible.

Internal Circulation

Nutrients and other particles are mainly circulated through internal fluid current generated by beating flagella. When the internal water pressure differs from that of outside, water from the inside naturally beigns to draw out of the cell. Moreover, the amount of water that passes through the organism can be regulated by contricting and relaxing the tiny holes outside of the cell.

Sponges do not move and are essentially an intricate water-filtering system. All poriferans have a canal-like system in which they pump water throughout the organism. Water enters the pores called the ostia, then flows through canals to a chamber called the spongocoel, and then exits through openings known as oscula. Because sponges don't have any specialized reproductive, digestive, respiratory, sensory, or excretory systems, this is the most advanced transport system in the organism (2). (AG)

The term Porifera means pore-bearing. Sponges are covered in tiny pores which lead to an internal canal system which lead to one or more large holes (the openings on the outside of the sponge (SL 5).

(SL 6)

Chemical Control

While the silica sponge is structurally limited in many universal processes, it does manage to utilize its pores for circulation, excretion, diffusion and respiration.
The silica sponge does not have a nervous system. Silica sponges also do not form a kidney, liver, coelom, and other various organs. Instead of using neurons for coordination and other functions the silica sponge has cells called pinacocytes. These pinacocytes function as simple muscles because it does not need the extremely complex systems that larger more complex organisms have. The muscles cover the exterior surface and contract to decrease the rate of water flow and the size of the silica sponge (9). The individual cell can sense and react to the environment. The cells are loose, not tissues, and not specialized (10). (SM)

Review Questions
1.Explain how cells on the outside of the silica sponge can filter and circulate nutrients and extra water throughout its body. (SM)
2. How does the porous structure of the silica sponge allow it to carry out its regular functions? (LK)
3. Explain how choanocytes play a role in gas exchange, allowing the sponges to interact with their environment. (SM)
4. How do silica sponges use chemicals to defend themselves? (JM)
5. The silica fibers from which the organism is made allow it to carry out different functions. Explain how these fibers help it to conduct functions necessary to life. (RG)

3. Ramel, Gordon R. "The Phylum Porifera." The Sponges (Phylum Porifera). N.p., n.d. Web. 18 Nov. 2013.

8. Thoms, Carsten. "Sponge Ecology." //Sponge Ecology//. N.p., n.d. Web. 21 Nov. 2013.
9. "Animal Planet." Animal Planet. N.p., n.d. Web. 23 Nov. 2013.
10. "Investigation." Life of a Sponge. N.p., n.d. Web. 23 Nov. 2013.
11. Ruppert, E. E., Fox, R. S., and Barnes, R. D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 76–97.
12. Bergquist, P. R. (2001). "Porifera (Sponges)". Encyclopedia of Life Sciences. John Wiley & Sons, Ltd.
13. Colugo. "Investigation." Life of a Sponge. Tree of Life, n.d. Web. 23 Nov. 2013.
15. Crow, James M. "Guessing Nature's Silica Secrets." // Royal Society of Chemistry, 15 Apr. 2008. Web. 25 Nov. 2013.
16."A SPECIAL Kick-Off!!!" //Project Special//. N.p., n.d. Web. 25 Nov. 2013.
17. "Physiology - Movement." Sponges. BotRejectsInc, n.d. Web. 25 Nov. 2013.
18. Sponge Diagram. Digital image. Biological Diversity. Estrella Mountain, n.d. Web. 25 Nov. 2013.
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20. "Pinacocytes, Collencytes, and Other Cell Types." Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 25 Nov. 2013.