Silica Sponge

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Classification/Diagnostic Characteristics
Silica sponge, capable of movement.
Silica sponge, capable of movement.

Sponges are animals which fall outside the category of Bilateria. Sponges are the simplest animals (they have no distinct tissue types), but have skeletal elements called spicules, which range in complexity. In silica sponges (glass sponges and demosponges), the spicules are comprised of hydrated [[#|silicon dioxide]]. A sponge is a collection of cells, water canals, spicules, elastic fibers, and molecules which form the extracellular matrix (1).

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This image shows the intriguing anatomy of Silica sponge.

Relationship to Humans

Sponges diverged from humans relatively long ago; our main commonality with sponges is that both species are animals (1).

A recent discovery shows that sponges share more than 70% common DNA with humans, some of which are responsible for cancer-causing agents. GIven how complex humans are and how relatively simple sponges are, this finding is unprecedented. (Prashant)

The original bath sponge was derived from specimens of sponge that have endoskeletons composed entirely of spongin fibers. Modern sponges, however, are made primarily from synthetic materials, even though some areas of the world, such as the Gulf of Mexico, still harvest sponges for this industry. More recently, sponges have been discovered to be sources of biomedical compounds, with various chemical substances secreted by sponges having anti-inflammatory, antibiotic, and anti-tumoral effects. Spongistatin 1, for instance, is a compound that has been proven to exhibit antimitotic properties, stunting the growth of cancerous tumours. In addition, sponges are vital indicators of marine environmental health. (Alexander Soloviev)
Sometimes given as wedding presents in Japan, they are valuable decorative pieces and the methods for removing soft tissue are well kept trade secrets though electron microscopy is a rumored possibility.

Habitat and Niche

Most sponges live in marine environments, though some live in freshwater (1).

99% of sponges live in in marine water, and some of which are freshwater sponges. They attach as far down as 8 kilometes in depth of the ocean floor. They cannot go too deep though, for if they delve into murky waters, the soot in the [[#|water clogs]] their pores that are vital to gaining important nutrients and oxygen for survival. (Prashant)

Predator Avoidance

A structural component of the sponge's skeleton, the spicules are considered to be a potential defense mechanism for the sponge. Research is still being done, but the presence of different types of spicules in various species seems to indicate that some types are for structural support and others are for defense. For example, monoaxonic spicules, like oxea-type spicules are designed to have two pointy ends, so they are assumed to be for defense. Sponges are also capable of regeneration, which is capable of regenerating, which isn't good for avoidance, but still beneficial post-attack. (

Nutrient Acquisition

Most species of sponge are filter feeders, meaning that they acquire nutrients passively. Water and dissolved food particles enter the pores of the sponge and pass through canals to a central atruim for digestion by choanocytes (1).

Sponges pump water to bring in oxygen and nutrients while removing wastes and carbon dioxide. Amoebyctes on the sponge help transport nutrients and form spicules, the sponge's skeletal fibers. They work together with other cells to digest foods and produce gametes for sexual reproduction in sponges. Choanocytes, which line the inner cavity, also collect food particles. They are used to filter nutrients and oxygen from flowing water and to catch sperm. (BHu)

They draw water in from their surrondings through their body wall, and into their central cavity. Their they have rings of tentacles with flagellum, called collar cells. When these flagellum move it makes a mini current that makes a barrier against water and then it pushed that water out of the top whole in the sponge known as the Osculum. While the water passes through the collar cells it captures food which is then absorbed and digested with food vaculoes and later transferred into the middle layer of the body known as the amoeboid cells.

Reproduction and Life Cycle

Sponges can reproduce both sexually and assexually. Sexual reproduction involves sperm from one organism diffusing in the water so that it can reach and fertilize the eggs of another organism. Each sponge carries both sperm and egg. Assexual reproduction involves budding and regeneration (1).
Sponges can reproduce sexually, with meiosis, and asexually, through budding
Sponges can reproduce sexually, with meiosis, and asexually, through budding

Most sponges also contain both the male and female reproductive organs, which further enhances the ease of which they reproduce asexually.This is when a small piece of sponge breaks off, but then grows into its own being, resulting in a genetically-identical clone. Sexual reproduction of the sponge involves a single spinge playing the male part, since they can play either the male or female role, releasing the sperm into the ocean's depths. This travels down into the female spinge to which a larva is released, which floats around until it grows into a full-bodied sponge. (Prashant)

For the formation of the strong and stiff bio-silica skeleton of sponges a hardening process is required that occurs when channels open releasing water and allows for the bio-silica polycondensation reaction. (4)

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Growth and Development

Sponges grow in different forms depending if it grows in high or low wave energy areas. If it grows in an area where there are surge channels on the open coast, the texture is stiffer and stronger. The "tissue" density is greater, the spicule content higher, and internal water channels narrower. If it is in an area where there are [[#|floating docks]], its texture is softer and more crumbly. (3)


Sponges have no specialized tissues (1).

Sponges consist of 3 layers: (1) an outer layer of flattened contractile epithelial cells (pinacocytes); (2) an inner, non-living gelatinous layer containing amoebocytes, which perform several functions in reproduction, secrete skeletal materials, and, most importantly, carry food particles from the choanocytes to the epithelial and other non-feeding cells; and (3) an inner layer of flagellated collar cells (choanocytes) that circulate seawater within and through the sponge to bring in food and reproductive products and help discharge waste products.
Taken from the website:

Sponges are divided into three distinct classes. The Calcarea have spicules of calcium carbonate in the calcite form and are commonly known as "calcareous" sponges. The Demospongiae, which is the most diverse class of sponges, have skeletons of two components, a mineral skeleton of silica spicules, and an organic skeleton made of diverse forms of spongin (collagen) fiber. Some sponges lack spicules, some lack fiber, and some combine the two. Some incorporate sand into their skeleton to various degrees. Some demosponges (the "sclerosponges") form a stony base of calcium carbonate in the aragonite form, with a veneer of living "tissue" on the surface. These sponges also produce silica spicules. The Hexactinellida, commonly known as the glass sponges, have siliceous spicules with a hexactine (six-ray) design. The growth form of sponges varies immensely, from thin encrusting to massive hemispherical forms, from branching and tree-like forms, to plate or vase shapes, to spherical-, barrel- or volcano-shaped forms. The sponge texture is highly diverse, varying from dense, stony, coral-like cups to smooth, slippery, skin-like structures, and reflects the underlying architecture of the spicules and fibers and the relative proportions and arrangements of these components of the skeleton. These characters (spicules and fibers) are fundamental to the way that we classify sponges, with skeletal arrangements characterizing groups of sponges that are related to each other.
Taken from the website:


Sponges are adapted to resist movement caused by water currents. Instead, they adhere to surfaces (such as rocks) and wait for food to bump into them (1).

Sensing the Environment

As adults,Sponges lack a nervous system, and thus have no nerve or sensory cells. However, as larva, they have the gentic potential for a nervous sytem, indicating that either sponges had the orgins of a nervous sytem, or that at some poin they had it, and then they lost it.

Gas Exchange

Gas exchange occurs through diffusion from the outside environment to the cells, which takes in oxygen and releasees carbon dioxide. [2]

Waste Removal

Waste is passively removed through water channels (1).
It is common for sponges to have ambient currents for water that extend above (similar to a wave) and over excurrent water openings (opening that send water out of the sponge). This creates pressure, thus allowing for more efficient removal of water from the sponge. Water is so important is has the ability to hold as much of 90% of the bacteria found within sponges.-

Environmental Physiology

Sponges are generally adapted to the temperature and salt concentration of their habitat (1).

Internal Circulation

Because sponges lack specialized cells, they instead use structure to determine internal circulation. Sponges are pourous, and water and nutrients travel directly into the sponge and are absorbed directly by cells towards the interior of the sponge. In this way, the sponge does not have an internal ciculation system, but allows for internal circulation using naturally occuring currents, thereby saving energy. (5)

Chemical Control

Sponges lack an endocrine system.

Review Questions:
1. A sponges is formed by a collection of these five different structures and molecules?
2. How do the spicules in the sponge differ in their functions?
3. How do sponges survive without any means of specialized cells for circulation or movement?
4. Silica sponges can reproduce both sexually and asexually. Compare and contrast the two methods of reproduction.


1. Principles of Life, by Hillis, Sadava, Heller, and Price