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It has been suggested that this article or section be merged with pinacoderm, spongocoel, sclerocyte and osculum (Discuss) |
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This article is about the aquatic animal. For the porous cleaning tool, see Sponge (tool). For other uses, see Sponge (disambiguation).
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The sponges or poriferans (from Latin porus "pore" and ferre "to bear") are animals of the phylum Porifera. Porifera translates to "Pore-bearer". They are primitive, sessile, mostly marine, water dwelling filter feeders that pump water through their bodies to filter out particles of food matter. Sponges represent the simplest of animals. With no true tissues (parazoa), they lack muscles, nerves, and internal organs. Their similarity to colonial choanoflagellates shows the probable evolutionary jump from unicellular to multicellular organisms. There are over 5,000 modern species of sponges known, and they can be found attached to surfaces anywhere from the intertidal zone to as deep as 8,500 m (29,000 feet) or further. Though the fossil record of sponges dates back to the Neoproterozoic Era, new species are still commonly discovered. Two examples would be a coral reef and a sponge.
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Sponges have several cell types:
Sponges have three body types: asconoid, syconoid, and leuconoid.
Asconoid sponges are tubular with a central shaft called the spongocoel. The beating of flagella forces water into the spongocoel through pores in the body wall. Choanocytes line the spongocoel and filter nutrients out of the water.
Syconoid sponges are similar to asconoids. They have a tubular body with a single osculum, but the body wall is thicker and more complex than that of asconoids and contains choanocyte-lined radial canals that empty into the spongocoel. Water enters through a large number of dermal ostia into incurrent canals and then filters through tiny openings called prosopyles into the radial canals. There food is ingested by the choanocytes. Syconoids do not usually form highly branched colonies as asconoids do. During their development, syconoid sponges pass through an asconoid stage.
Leuconoid sponges lack a spongocoel and instead have flagellated chambers, containing choanocytes, which are led to and out of via canals.
It should be noted that these 3 body grades are useful only in describing morphology, and not in classifying sponge species.
Sponges have no true circulatory system; instead, they create a water current which is used for circulation. Dissolved gases are brought to cells and enter the cells via simple diffusion. Metabolic wastes are also transferred to the water through diffusion. Sponges pump remarkable amounts of water. Leuconia, for example, is a small leuconoid sponge about 10 cm tall and 1 cm in diameter. It is estimated that water enters through more than 80,000 incurrent canals at a speed of 6cm per minute. However, because Leuconia has more than 2 million flagellated chambers whose combined diameter is much greater than that of the canals, water flow through chambers slows to 3.6cm per hour.See Hickman and Roberts (2001) Integrated principles of zoology — 11th ed., p.247 Such a flow rate allows easy food capture by the collar cells. All water is expelled through a single osculum at a velocity of about 8.5 cm/second: a jet force capable of carrying waste products some distance away from the sponge.
Sponges are classified as animals, despite the fact that they lack gastrulated embryos, extracellular digestive cavities, nerves, muscles, tissues, and obvious sensory structures, which all other animals possess. At one time, sponges were considered plants, as they appear to share the plant-like characteristic of being rooted to a single spot, although some species of sponge are motile. Unlike almost all plants, sponges do not photosynthesize, and they lack cellulose cell walls, which are common to all plants.
Long thought to be the most archaic branch of the animals, sponges are considered as useful models of the earliest multicellular ancestors of animals; although there is no evidence that they actually are, or that they are even descended from early animals. Sponge choanocytes (feeding cells) are likely to be an homologous cell type to choanoflagellates - a group of unicellular and colonial protists that are believed to be the immediate precursors of animals. Sponges appear to be, at best, a divergent side-group from the main animal line.[citation needed]
It has been suggested that the sponges are paraphyletic to the other animals. Otherwise they are sometimes treated as their own subkingdom, the Parazoa. Similar fossil animals known as Chancelloria are no longer regarded as sponges.[citation needed]
One phylogenetic hypothesis based on molecular analysis proposes that the phylum Porifera is itself paraphyletic, and should be split into two new phyla, the Calcarea and the Silicarea.[citation needed]
Sponges are divided into classes based on the type of spicules in their skeleton. The three classes of sponges are bony (Calcarea), glass (Hexactenellida), and spongin (Demospongiae). Some taxonomists have suggested a fourth class, Sclerospongiae, of coralline sponges, but the modern consensus is that coralline sponges have arisen several times and are not closely related.R. C. Brusca and G. J. Brusca (2003). Invertebrates. Second Edition. Sunderland, Mass.: Sinauer Associates. In addition to these four, a fifth and extinct class has been proposed: Archaeocyatha. While these ancient animals have been phylogenetically vague for years, the current general consensus is that they were a type of sponge.[citation needed]
Although 90% of modern sponges are demosponges, fossilized remains of this type are less common than those of other types because their skeletons are composed of relatively soft spongin that does not fossilize well. The fossil Archaeocyantha may also belong here, though their skeletons are solid rather than separated into spicules.
Fossil sponge Raphidonema faringdonense from the Cretaceous of England
The fossil record of sponges is not abundant, except in a few scattered localities. Some fossil sponges have worldwide distribution, while others are restricted to certain areas. Sponge fossils such as Hydnoceras and Prismodictya are found in the Devonian rocks of New York state. In Europe the Jurassic limestone of the Swabian Alps are composed largely of sponge remains, some of which are well preserved. Many sponges are found in the Cretaceous Lower Greensand and Chalk Formations of England, and in rocks from the upper part of the Cretaceous period in France. A famous locality for fossil sponges is the Cretaceous Faringdon Sponge Gravels in Faringdon, Oxfordshire in England. An older sponge is the Cambrian Vauxia. Sponges have long been important agents of bioerosion in shells and carbonate rocks. Their borings extend back to the Ordovician in the fossil record.
Fossil sponges differ in size from 1 cm (0.4 inches) to more than 1 meter (3.3 feet). They vary greatly in shape, being commonly vase-shapes (such as Ventriculites), spherical (such as Porosphaera), saucer-shaped (such as Astraeospongia), pear-shaped (such as Siphonia), leaf-shaped (such as Elasmostoma), branching (such as Doryderma), irregular or encrusting.
Detailed identification of many fossil sponges relies on the study of thin sections.
Modern sponges are predominantly marine, with some 150 species adapted to freshwater environments. Their habitats range from the inter-tidal zone to depths of 6,000 metres (19,680 feet). Certain types of sponges are limited in the range of depths at which they are found. Sponges are worldwide in their distribution, and range from waters of the polar regions to the tropical regions. Sponges are most abundant in both numbers of individuals and species in warmer waters.
Adult sponges are largely sessile, and live in an attached position. However, it has been noted that certain sponges can move slowly by directing their water current in a certain direction with myocytes. The greatest numbers of sponges are usually to be found where a firm means of fastening is provided, such as on a rocky ocean bottom. Some kinds of sponges are able to attach themselves to soft sediment by means of a root-like base. Sponges also live in quiet clear waters, because if the sediment is agitated by wave action or by currents, it tends to block the pores of the animal, lessening its ability to feed and survive.
Recent evidence suggests that a new disease called Aplysina red band syndrome (ARBS) is threatening sponges in the Caribbean.[1] Aplysina red band syndrome causes Aplysina to develop one or more rust-coloured leading edges to their structure, sometimes with a surrounding area of necrotic tissue so that the lesion causes a contiguous band around some or all of the sponge\'s branch.
Sponges can reproduce sexually or asexually.
Asexual reproduction is through internal and external budding. External budding occurs when the parent sponge grows a bud on the outside of its body. This will either break away or stay connected. Internal budding occurs when archaeocytes collect in the mesohyl and become surrounded by spongin. The internal bud is called a gemmule, and this is seen only in the freshwater sponge family, the Spongillidae. An asexually reproduced sponge has exactly the same genetic material as the parent.
In sexual reproduction, sperm are dispersed by water currents and enter neighbouring sponges. All sponges of a particular species release their sperm at approximately the same time.[citation needed] Fertilization occurs internally, in the mesohyl. Fertilized oocytes develop within the mesohyl. Cleavage stages are highly varied within and between groups, sometimes even within a single species. Larval development usually involves an odd type of morphogenetic movement termed an inversion of layers. When this occurs in some species (for example, in Sycon coactum ), the larva flips into the choanocyte chamber, and then can emerge via the water canal system and out through the osculum.
Although sponges are hermaphroditic (both male and female), they are not self-fertile. Most sponges are sequential hermaphrodites, capable of producing eggs or sperm, but not both at the same time.
In 1997, use of sponges as a tool was described in 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.Smolker, R.A., et al.. "Sponge-carrying by Indian Ocean bottlenose dolphins: Possible tool-use by a delphinid }". The behaviour, known as sponging, has only been observed in this bay, and is almost exclusively shown by females. This is the only known case of tool use in marine mammals outside of Sea Otters. An elaborate study in 2005 showed that mothers most likely teach the behaviour to their daughters.Krutzen M, Mann J, Heithaus MR, Connor RC, Bejder L, Sherwin WB (2005). "Cultural transmission of tool use in bottlenose dolphins". Proceedings of the National Academy of Sciences 102 (25): 8939–8943.
In common usage, the term sponge is applied to the skeleton of the animal, from which the tissue has been removed by maceration and washing, leaving just the spongin scaffolding. Calcareous and siliceous sponges are too harsh for similar use. Commercial sponges are derived from various species and come in many grades, from fine soft "lamb\'s wool" sponges to the coarse grades used for washing cars.
The manufacture of rubber-, plastic- and cellulose-based synthetic sponges has significantly reduced the commercial sponge fishing industry in recent years.
The luffa "sponge", also spelled "loofah," commonly sold for use in the kitchen or the shower, is not derived from an animal sponge, but from the locules of a gourd (Cucurbitaceae).
Sponges have medicinal potential due to the presence of antimicrobial compounds in either the sponge itself or their microbial symbionts.See e.g. Teeyapant R, Woerdenbag HJ, Kreis P, Hacker J, Wray V, Witte L, Proksch P. (1993) Antibiotic and cytotoxic activity of brominated compounds from the marine sponge Verongia aerophoba. Zeitschrift für Naturforschung. C, Journal of biosciences 48:939–45.
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