![]() In addition Archaeocyathids, whose fossils are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge.Ĭells of the protist choanoflagellate clade closely resemble sponge choanocyte cells. Fossils of all of these types have been found in rocks dated from 580 million years ago. The fragile glass sponges, with " scaffolding" of silica spicules, are restricted to polar regions and the ocean depths where predators are rare. Calcareous sponges, which have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate is easiest. ![]() Demosponges constitute about 90% of all known sponge species, including all freshwater ones, and they have the widest range of habitats. Demosponges use spongin many species have silica spicules, whereas some species have calcium carbonate exoskeletons. More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers, or both. In most sponges, an internal gelatinous matrix called mesohyl functions as an endoskeleton, and it is the only skeleton in soft sponges that encrust such hard surfaces as rocks. When environmental conditions become less hospitable to the sponges, 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 they then either form completely new sponges or recolonize the skeletons of their parents. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. The fertilized eggs develop into larvae, which swim off in search of places to settle. Most species that use sexual reproduction release sperm cells into the water to fertilize ova that in some species are released and in others are retained by the "mother". Sponges reproduce both asexually and sexually. A few species of sponges that live in food-poor environments have evolved as carnivores that prey mainly on small crustaceans. Although there are freshwater species, the great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding 8,800 m (5.5 mi).Īlthough most of the approximately 5,000–10,000 known species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts, and these alliances often produce more food and oxygen than they consume. All adult sponges are sessile aquatic animals, meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel) while in larval stage of life they are motile. Many sponges have internal skeletons of spicules (skeletal-like fragments of calcium carbonate or silicon dioxide), and/or spongin (a modified type of collagen protein). The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where the water deposits nutrients and then leaves through a hole called the osculum. Some of them are radially symmetrical, but most are asymmetrical. Unlike other animals, they lack true tissues and organs. ![]() Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spirastrella coccinea, and the gray rope sponge, Callyspongia sp. Overview Sponge biodiversity and morphotypes at the lip of a wall site in 60 feet (20 m) of water. The term sponge derives from the Ancient Greek word σπόγγος ( spóngos 'sponge'). Sponges were possibly the first to branch off the evolutionary tree from the last common ancestor of all animals, which would make them the sister group of all other animals. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges do not have complex nervous, digestive or circulatory systems like humans. Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Sponges, the members of the phylum Porifera ( / p ə ˈ r ɪ f ər ə/ meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts.
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