Porifera

Description

The histological structure of sponges is more particular in the case of sponges, they are diblastic.

external Membrane or Ectoderm : the épidermiques cells, which compose the exoderme, are called pinacocytes, and the porocytes, which are hollow cells, allowing the drainage duct towards the interior of sponge.
internal Membrane or Endoderm : it is made of cells with flange called Choanocyte S. These cells are also whipped in order to ensure a water circulation and a retention of food.

The sponges form the simplest organization: they are colonies of practically undifferentiated cells, without real internal structures, nor operation. They are animals without Nervous system nor digestive Tract.

The essential functionality acquired by sponges is simple: it is the capacity with living in company. The capacity for cells to be different according to its position in a group is already observable in the protozoa. The sponges systematize this organization, and make it permanent. Certain colonies of sponges takes part in the construction of underwater solid mass, of other like the Cliona , are perforating.

The various groups of sponge in a strict sense are characterized by the nature of the interstitial skeleton that these colonies use to acquire a rigid structure: limestone, chitin or silica. The selective advantage of a rigid structure is in the protection which it brings: it is more difficult with brouter for a predator. As always in the long run, evolutionary success finally was not in these rigid and protective structures. Evolutionary success was in flexible structures capable of movements, which one finds with the Cnidaire S.

Anatomy

These two cellular layers are separated by a acellulaire layer similar to frost (Mésoglée) in which tiny needles (spicules) which can be Calcaire S, siliceous or consist of a substance cornea (Spongine) reinforce and rigidify the structure. The spicules are insulated or welded the ones with the others in a rigid reinforcement.

The marketed sponge is in fact only the skeleton of a Démosponge. ( Euspongia ) which comes only from the hot moderate seas.

The internal cavity (atrium) communicates with outside by two types of openings: perforated cells (porocytes) and inhaling pores (ostia). The multitude of pores allows water to cross various cellular fabrics to arrive in the atrium. Water is thus filtered then evacuated by a larger opening (the oscule). According to the complexity of sponge, this one can present several oscules. Once captured food, of the mobile cells (Amibocyte S) distribute the nutrients between the other cells.

The evolution made so that it is possible to recognize three body forms at the porifères. The form Asconoïde, simplest of the three, meets only at smallest sponges and is characterized by ostia leading directly to the Spongocoele, which is papered of choanocytes. The form Syconoïde represents an evolution compared to the first form, because the choanocytes do not paper any more the spongocoele but rather a multitude of small channels, the radiate channels, which have the advantage of increasing the surface of contact between the water and the cells of the animal, allowing a more great absorption of food. Finally, the form Leuconoïde is most complex, with the ostia and channels leading to many papered rooms of choanocytes. One meets this form at large colonial sponges.

Food

The very great majority of sponges are Suspensivore S. Certaines species can filter 10.000 to 20.000 times their volume of water in only one day. This strategy requires neither complex structure, nor coordinated movement. However a recent discovery gives a report on the existence of a carnivorous sponge for certain sponges depths.

Regeneration

The sponges are able to be regenerated. They can undergo an important dehydration (to be out of water) during several years and live again once replongées in their natural biotope. On the other hand, they are generally, very sténohalines (they do not support the variations of Salinité).

They are practically immortal when the conditions theirs are favorable.

Reproduction

Sexuée reproduction

The majority of sponges are hermaphrodites. The Gamète S (Spermatozoon S and Ovule S) come from the Choanocyte S. the spermatozoa are expelled by an individual and penetrate in another sponge. The choanocytes having captured a spermatozoon become mobile and transport the spermatozoa through mésoglée where the ovules are. After the Fecundation, the egg develops in mésoglée then becomes a Larve, covered with Flagelle S, which is released in the external medium. The small proportion of larvae which succeed in surviving will be fixed on a support and to metamorphose adult sponge.

Asexual reproduction

The sponges have also a capacity of regeneration: they can replace lost parts. They can also reproduce in an asexual way thus. Detached fragments can reform a whole sponge. This characteristic is used to allow the multiplication of sponges of toilet.

Chorology

Distribution

They are abundant between 6 and 20 meters, one finds some up to 8500 Mr.

Ecology

The sponges are, except exceptions, sessile i.e. of the sedentary animals which live on a substrate. In general, one meets them in the littoral zones and sublittorales where food is abundant, but some species are up to 5.000 m of depth. The sponge is nourished by attracting water towards it, entering by the inhaling pores, and while filtering the nutritive particles (organic phytoplanktons, bacteria, remains). Water thus filtered is then expelled by an opening upwards.

The sponges can be used as shelters with multiple animals known as commensaux which benefit from the contributions in food that provides them the sponge host. The species of the kind Hyalonema shelter worms and small shellfish living in Symbiose. It can also exist of associations of the type mutualism. Ficulina ficus can be fixed on the shell sheltering a Bernard the hermit who is thus protected. There exist in addition parasitic sponges like Cliona celata which is fixed on oyster shells and can transpierce them.

Certain sponges have a role in the biogeochemical Cycle of the Calcium in the oceans by breaking up the rocks or the shells limestones.

The majority of sponges are marine, but there exists about fifty species living in fresh water. For example, the spongille Spongilla lacustris saw fixed on the watery stones or plants.

Substances making it possible to defend against Predatory S or micro-organisms parasite S were discovered. These substances are of pharmacological interest : the spongopurine has antiviral properties, the spongopiridine present of the antitumor properties. Other molecules have properties Antibiotique S.

Certain sponges take part in bioconstructions. Constructions with archéocyathes of Cambrien, paramount role of the stromatopores in the most turbulent zones of the reefs siluro-dévoniens, biohermes with spongiaires of Oxfordien… Others take part in the bioérosion. The mass of sediments produced starting from this activity of perforating sponges is considerable.

Predator

Certain sponges is known to be very toxic for certain organizations Spongivore S. It is the case in particular Aaptos aaptos , Chondrilla nucula , Tethya actinia , Spheciospongia vesparium and Suberites domuncula . The overlapping tortoises are only the Tétrapode with being spongivore. The spicules which form the skeleton of certain sponges protect them from certain predatory.

Origin

Systematic

The spongiaires are a very old group, very abundant in the sediments paleontological. In the Years 1970, old relics made it possible to allot to the spongiaires various groups formerly considered as Cnidaire S. To the beginning of the Années 2000, with the development of systematic molecular, it was possible to check the assumptions for the morphological homology and the evolutionary assumptions which result from this. Several species of Astrophorida were séquencées for a fragment of ADNr 28S. Those which were examined presented many characteristics morphological and certain of these characters could be revalued according to the molecular data. The results on the order of the Astrophorida are in contradiction with historical classification. Classification is likely to be upset about it.

Taxonomy

The spongiaires or sponges represent approximately 9000 species distributed in various units:

the siliceous sponges

the Démosponge S: have Spicule S siliceous of one, three or four points. The sponge of toilet belongs to the démosponges.
the hexactinellides or sponges of glass: siliceous spicules with six points have. They are rare with less than 200 m of depth. They reach their greater diversity between 200 m and 600 m (zone bathyale).

the sponges limestones: have a calcareous skeleton. The calcisponges more abundant and are diversified in not very deep water (< 100 m).
the Archéocyathidés is a group disappeared at the end from the Cambrien.

Their scientific names in traditional Classification are:

class Demospongiae Solas, 1885 - démosponges
class Hexactinellida Schmidt, 1870 - hexactinellides
class Calcarea Bowerbank, 1864 - sponges limestones

Place des sponges in the animal world

Fossils

The fundamental histological structure is not perceptible in a fossil state and the determination of the species must be done by the microstructural study which obliges to know the whole of existing sponges during the process of biomineralisation. The spicules of certain rocks are so abundant that they can constitute the principal element of it. It is the case of the Gaize S and Spongolite S.

The sponges of the Paleozoic and the beginning of the Mesozoic were sponges which took part in the construction of underwater solid masses and lived in not very deep marine water. With the Jurassic , the hexactinellides are disappeared from not very deep water for depths which are, except exception, from at least 200 Mr.

Sponges and the man

The spongiaires have been used for several centuries like sponges. Those which are marketed are deprived of spicules but of the organic part in spongin. The species most usually used for this purpose are the Euspongia which live in the Mediterranean, but other species of different origins can be used like such.

See too

taxinomic Photo-guide of the animal world
Démosponge
Sponges hexactinellides
Sponges limestones

external references

External bonds

Tree of life:
Hunting for the sponge Taxonomy, phylogeny and biogeography of the spongiaires of the Area of the Fjords of the south of Chile
uhp Nancy on the sponges

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