Spugna - Porifera
Spugna Porifera organismi pluricellulari Sponges multicellular organisms
Sponges (Porifera Grant, 1836, from the Latin bearers of pores) or sponges are an animal phylum. It is multi-cellular organisms, having pores rich bodies and channels that allow water to flow through them; They are basically made up of a lot, or spongocele, structured as a compound or gelatinous mesoglea placed between two thin layers of cells, the coanoderma, pinacoderma interior and the exterior.
The non-differentiated cells in the mesoglia, or archeoblasti, able to transform to take on specialized functions, can migrate between the layers of main cells and the mesoglia. They possess a skeletal structure, the endoskeleton, formed by calcareous or siliceous spicules, or consist of protein fibers spongin, produced by specialized cells. Sponges do not have equipment or different organs; most of the functions are based on maintaining a constant flow of water through their bodies to obtain food and oxygen and remove catabolic products.
Generality Sponges are, like the other metazoan, multicellular, heterotrophic, they do not have cell walls and produce sperm and ovules. Unlike other animals, they do not have real tissues and organs, and, generally, do not have somatic symmetry. The shapes of their bodies are adapted for maximum efficiency of the flow of water through the central cavity, where it deposits nutrients, and exits through a hole called osculum. The interior of skeletons are spongine and / or formed by spicules of calcium carbonate or silica. All Sponges are aquatic animals, mostly marine and sessile; There are also freshwater species, and colonize environments ranging from tidal zones at depths exceeding 8000 m.
Evolution The taxonomists place the sponges in one of four sottoregni animals, that of Parazoi. Molecular analysis since 2001 have concluded that some groups of sponges are more closely related to the eumetazoi (the vast majority of animal organisms) than the rest of sponges. These findings imply that sponges are not a monophyletic group since the last common ancestor of all the sponges would also be a direct ancestor of eumetazoi, which are not sponges. A study conducted on the basis of comparisons of ribosomal DNA has concluded that the most important division within the phylum is among glassy or Hexactinellid sponges and the rest of the group, and that eumetazoi are more closely related to calcareous sponges, the ones with spicules calcium carbonate, compared to other types of sponge. In 2007, an analysis based on the comparison of RNA and another based primarily on comparison of spicules concluded that demosponge and glass sponges are more closely related to each other than other classes, like the calcareous sponges, which in turn are more closely linked to eumetazoi.
These and other analyzes have established that the sponges are the closest relatives of the common ancestors to all metazoans, that all multicellular animals. Another comparison in 2008 of 150 genes in each of 21 species ranging from fungi to humans, but including only two species of sponge, suggested that Ctenophora are the most basal lineage of metazoans sampled. If this is correct, modern Ctenophora have developed their complex structures independently of other metazoans, or the ancestors of sponges “were more complex” and all known sponges have been drastically simplified in the forms.
The study recommends further analysis using a wider range of sponges and other simple metazoan as placozoi. The results of this analysis, published in 2009, suggest that the return to the previous view, with the sponges to the evolutionary tree based, can be justified. a dendrogram constructed using a combination of all available data, morphological, developmental and molecular concluded that the sponges are actually a monophyletic group, with the twin group cnidarians formats to bilateria.
The first evidence of the existence of fossil Porifera date back about 570 million years ago (late Precambrian): the finds of that period, the so-called small shelly fauna (from English small shelly fauna), are composed largely of clusters spicules of sponges, together with fragments or disarticulated remains of other organisms such as mollusks, brachiopods, echinoderms.