Sponge

Sponges are animals of the phylum Porifera (Pore bearer) (). Their bodies consist of jelly-like mesohyl sandwiched between two thin layers of cells. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells that can transform into other types, often migrating between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow. All are sessile aquatic animals and, although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding . While most of the approximately 5,000-10,000 known species feed on bacteria and other food particles in the water, some host photosynthesizing micro-organisms as endosymbionts and these alliances often produce more food and oxygen than they consume. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans.

Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding. When conditions deteriorate, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules, "survival pods" of unspecialized cells that remain dormant until conditions improve and then either form completely new sponges or re-colonize the skeletons of their parents.

However most sponges use sexual reproduction, releasing sperm cells into the water. In viviparous species the cells that capture most of the adults' food capture the sperm cells but, instead of digesting them, transport them to ova in the parent's mesohyl. The fertilized eggs begin development within the parent and the larvae are released to swim off in search of places to settle. In oviparous species both sperm and egg cells are released into the water and fertilisation and development take place outside the parent's bodies.

Sponges use various materials to reinforce their mesohyl and in some cases to produce skeletons, and this forms the main basis for classifying sponges. Sponges produce spicules made of calcium carbonate. Demosponges reinforce the mesohyl with fibers of a special form of collagen called spongin, most also produce spicules of silica, and a few secrete massive external frameworks of calcium carbonate. Although glass sponges also produce spicules made of silica, their bodies mainly consist of syncytia that in some ways behave like many cells sharing a single external membrane, and in others like individual cells with multiple nuclei. Probably because of their variety of construction methods, demosponges constitute about 90% of all known sponge species, including all freshwater ones, and have the widest range of habitats. Calcareous sponges are restricted to relatively shallow marine waters where production of calcium carbonate is easiest. The fragile glass sponges are restricted to polar regions and the ocean depths where predators are rare, and their feeding systems very efficiently harvest what little food is available. Fossils of all of these types have been found in rocks dated from . In addition Archaeocyathids, whose fossils are common in rocks from but not after , are now regarded as a type of sponge.

It is generally thought that sponges' closest single-celled relatives are choanoflagellates, which strongly resemble the cells that sponges use to drive their water flow systems and capture most of their food. It is also generally agreed that sponges do not form a monophyletic group, in other words do not include all and only the descendants of a common ancestor, because it is thought that Eumetazoa (more complex animals) are descendants of a sub-group of sponges. However it is uncertain which group of sponges is closest to Eumetazoa, as both calcareous sponges and a sub-group of demosponges called Homoscleromorpha have been nominated by different researchers. In addition a study in 2008 suggested that the earliest animals may have been similar to modern comb jellies. Since comb jellies are considerably more complex than sponges, this would imply that sponges had mobile ancestors and greatly simplified their bodies as they adapted to a sessile filter feeding lifestyle. Chancelloriids, sessile, bag-like organisms whose fossils are found only in rocks from the Cambrian period, increase the uncertainty as it has been suggested that they were sponges but also that their external spines resemble the "chain mail" of the slug-like Halkieriids.

The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. However by the 1950s these had been over-fished so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging.

Distinguishing features

Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multi-celled animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. However, a few carnivorous sponges have lost these water flow systems and the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina").]]-->

Cell types

A sponge's body is hollow and is held in shape by the mesohyl, a jelly-like substance made mainly of collagen and reinforced by a dense network of fibers also made of collagen. The inner surface is covered with choanocytes, cells with cylindrical or conical collars surrounding one flagellum per choanocyte. The wave-like motion of the whip-like flagella drives water through the sponge's body. All sponges have , channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like porocytes that form closable inlet valves. Pinacocytes, plate-like cells, form a single-layered skin over all other parts of the mesohyl that are not covered by choanocytes, and the external pinacocytes also digest food particles that are too large to enter the ostia, Instead of choanocytes they have further syncytia, known as choanosyncytia, which form bell-shaped chambers which water enters via perforations. The insides of these chambers are lined with "collar bodies", each consisting of a collar and flagellum but without a nucleus of its own. The motion of the flagella sucks water through passages in the "cobweb" and expels it via the open ends of the bell-shaped chambers. Traces of the chemical 24-isopropylcholestane have been found in rocks formed . This is a stable derivative of 24-isopropylcholesterol, which is thought to be produced by demosponges but not by eumetazoans ("true animals", i.e. cnidarians and bilaterians). Since choanoflagellates are thought to be animals' closest single-celled relatives, a team of scientists examined the biochemistry and genes of one choanoflagellate species. They concluded that this species could not produce 24-isopropylcholesterol but that investigation of a wider range of choanoflagellates would be necessary in order to prove that the fossil 24-isopropylcholestane could only have been produced by demosponges.

Silica spicules like those of demosponges have been reported from Nevada in rocks dated around . Well-preserved fossil sponges from about in the Ediacaran period have been found in the Doushantuo Formation. These fossils, which include spicules, pinacocytes, porocytes, archeocytes, sclerocytes and the internal cavity, have been classified as demosponges. Fossils of glass sponges have been found from around in rocks in Australia, China and Mongolia. Calcium carbonate spicules of calcareous sponges have been found in Early Cambrian rocks from about in Australia. Other probable demosponges have been found in the Early Cambrian Chengjiang fauna, from . Freshwater sponges appear to be much younger, as the earliest known fossils date from the Mid-Eocene period about .

Archaeocyathids, which some classify as a type of coralline sponge, are common in the Cambrian period from about , but apparently died out by the end of the Cambrian .Simplified family tree showing calcareous sponges
as closest to more complex animals |- | Simplified family tree showing Homoscleromorpha
as closest to more complex animals |} In the 1990s sponges were widely regarded as a monophyletic group, in other words all of them descended from a common ancestor that was itself a sponge, and as the "sister-group" to all other metazoans (multi-celled animals), which themselves form a monophyletic group. On the other hand some 1990s analyses also revived the idea that animals' nearest evolutionary relatives are choanoflagellates, single-celled organisms very similar to sponges' choanocytes – which would imply that most Metazoa evolved from very sponge-like ancestors and therefore that sponges may not be monophyletic, as the same sponge-like ancestors may have given rise both to modern sponges and to non-sponge members of Metazoa.

Analyses since 2001 have concluded that Eumetazoa (more complex than sponges) are more closely related to particular groups of sponges than to the rest of the sponges. Such conclusions imply that sponges are not monophyletic, because the last common ancestor of all sponges would also be a direct ancestor of the Eumetazoa, which are not sponges. A study in 2001 based on comparisons of ribosome DNA concluded that the most fundamental division within sponges was between glass sponges and the rest, and that Eumetazoa are more closely related to Calcareous sponges, those with calcium carbonate spicules, than to other types of sponge.

Other anatomical and biochemical evidence links the Eumetazoa with Homoscleromorpha, a sub-group of demosponges. A comparison in 2007 of nuclear DNA, excluding glass sponges and comb jellies, concluded that: Homoscleromorpha are most closely related to Eumetazoa; calcareous sponges are the next closest; the other demosponges are evolutionary "aunts" of these groups; and the chancelloriids, bag-like animals whose fossils are found in Cambrian rocks, may be sponges. The sperm of Homoscleromorpha share with those of Eumetazoa features that those of other sponges lack. In both Homoscleromorpha and Eumetazoa layers of cells are bound together by attachment to a carpet-like basal membrane composed mainly of "type IV" collagen, a form of collagen not found in other sponges – although the spongin fibers that reinforce the mesohyl of all demosponges is similar to "type IV" collagen.

]] The analyses described above concluded that sponges are closest to the ancestors of all Metazoa, in other words of all multi-celled animals including both sponges and more complex groups. However, another comparison in 2008 of 150 genes in each of 21 genera, ranging from fungi to humans but including only two species of sponge, suggested that comb jellies (ctenophora) are the most basal lineage of the Metazoa included in the sample. If this is correct, either modern comb jellies developed their complex structures independently of other Metazoa, or sponges' ancestors were more complex and all known sponges are drastically simplified forms. The study recommended further analyses using a wider range of sponges and other simple Metazoa such as Placozoa. The results of such an analysis, published in 2009, suggest that a return to the previous view may be warranted. 'Family trees' constructed using a combination of all available data - morphological, developmental and molecular - concluded that the sponges are in fact a monophyletic group, and with the cnidarians form the sister group to the bilaterians.

Archaeocyathids are very common fossils in rocks from the Early Cambrian about but are not found after the Late Cambrian. It has been suggested that they were produced by: sponges; cnidarians; algae; foraminiferans; a completely separate phylum of animals, Archaeocyatha; or even a completely separate kingdom of life, labelled Archaeata or Inferibionta. Since the 1990s archaeocyathids have been regarded as a distinctive group of sponges.
{{Annotated image | float=left | caption=Halkieriid sclerite structure However another analysis in 2002 concluded that chancelloriids are not sponges and may be intermediate between sponges and more complex animals, among other reasons because their skins were thicker and more tightly-connected than those of sponges. In 2008 a detailed analysis of chancelloriids' sclerites concluded that they were very similar to those of halkieriids, mobile bilaterian animals that looked like slugs in chain mail and whose fossils are found in rocks from the very Early Cambrian to the Mid Cambrian. If this is correct, it would create a dilemma, as it is extremely unlikely that totally unrelated organisms could have developed such similar sclerites independently, but the huge difference in the structures of their bodies makes it hard to see how they could be closely related.

Taxonomy

--> .]] For a long time sponges were assigned to a separate subkingdom, Parazoa ("beside the animals"), separate from the Eumetazoa which formed the rest of the kingdom Animalia. However in the 1980s it was found that these were all members of either the Calcarea or the Demospongiae.

So far scientific publications have identified about 9,000 poriferan species, ************* -->

Use

By dolphins

A report in 1997 described use of sponges as a tool by bottlenose dolphins in Shark Bay. A dolphin will attach a marine sponge to its rostrum, which is presumably then used to protect it when searching for food in the sandy sea bottom. The behaviour, known as sponging, has only been observed in this bay, and is almost exclusively shown by females. A study in 2005 concluded that mothers teach the behaviour to their daughters, and that all the sponge-users are closely related, suggesting that it is a fairly recent innovation.

By humans

, Florida]] --> in Greece]]

Skeleton

The calcium carbonate or silica spicules of most sponge genera make them too rough for most uses, but two genera, Hippospongia and Spongia, have soft, entirely fibrous skeletons. Early Europeans used soft sponges for many purposes, including padding for helmets, portable drinking utensils and municipal water filters. Until the invention of synthetic sponges, they were used as cleaning tools, applicators for paints and ceramic glazes and discreet contraceptives. However by the mid-20th century, over-fishing brought both the animals and the industry close to extinction.

Many objects with sponge-like textures are now made of substances not derived from poriferans. Synthetic sponges include personal and household cleaning tools, breast implants, and contraceptive sponges. Typical materials used are cellulose foam, polyurethane foam, and less frequently, silicone foam.

The luffa "sponge", also spelled loofah, which is commonly sold for use in the kitchen or the shower, is not derived from an animal but from the fibrous "skeleton" of a gourd (Cucurbitaceae).

Antibiotic compounds

Sponges have medicinal potential due to the presence in sponges themselves or their microbial symbionts of chemicals that may be used to control viruses, bacteria, tumors and fungi.

See also

Aaptos kanuux

Randolph Kirkpatrick

Sponge reef

Sponge Reef Project

== References ==

Further reading

. . Bursztyn.px.pl, Collection Jurassic fossils sponges

External links

Water flow and feeding in the phylum Porifera (sponges) - Flash animations of sponge body structures, water flow and feeding

Bioerosion website at The College of Wooster

Carsten's Spongepage, Information on the ecology and the biotechnological potential of sponges and their associated bacteria.

Tarpon Springs, Florida sponge industry">History of Tarpon Springs, Florida sponge industry

Nature's 'fibre optics' experts

The Sponge Reef Project

Queensland Museum FAQ about sponges

Sponge Guide from Queensland Museum, John Hooper

Sponge Guide for Britain and Ireland, Bernard Picton, Christine Morrow & Rob van Soest

World Porifera database, the world list of extant sponges, includes a searchable database.