How do sponges differ from hydra?
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Sponges are Porifera; hydra are Cniderians.\n\nPorifera have body pores (ostia), canals and chambers that serve for passage of water. They also have choanocytes (collar cells) specialized cells that create water currents, as they are filter feeders.  \n\nCnidarians have stinging cells organelles called nematocytes or cnidocytes. They also have a nerve net with symmettrical and asymmetrical synapses.  They have a muscular system.
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I think you want to know the difference between a porpoises and a dolphin. (If that is the case, then consider my answer but if not then never mind. )\n\n>>Porpoises have spatulate (spade-shaped or flattened) teeth distinct from the conical teeth of dolphins.\n>>Porpoises are relatively r-selected compared with dolphins: that is, they rear more young more quickly than dolphins.\n>>Porpoises tend to be smaller but stouter than dolphins. \n>>Porpoise's dorsal fin is generally triangular, rather than falcate (curved) like that of many dolphins.\n>> Porpoises tend to be less acrobatic and more wary than dolphins.\n>>Porpoises are rarely held in captivity in zoos or oceanaria, as they are generally not as capable of adapting to tank life nor as easily trained as dolphins.\n>>Porpoises belong to the Family Delphinidae, while dolphins belong to the Family Phocoenidae. \n>>extended beak present in most dolphins is absent in most porpoises.\n>>Porpoises lack a melon, while the bulbous forehead is often observed in dolphins.\n>>Porpoises are rarely observed in groups of more than one or two individuals, in contrast of the dolphins.\n>>Dolphins can be observed bow-riding, or riding on the pressure wave of a large ship or whale, on passing vessels. Unlike dolphins, porpoises are rarely seen bow-riding.♥
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both are different species belonging to same genus
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Oceanic crust is fundamentaly different from Continental because of its origin.  Oceanic crust is formed as the continents move apart and new 'material' is forced between the plates.  You may have seen the video of lava being extruded at the bottom of the ocean 'toothpaste style'.  This forms round lumps of 'pillow lava' which have no crystals (because it cooled very quickly the crystals don't have time to form).  Below this you'll see the same material (chemically) but which forms columns of basalt (like Giant's causeway in Ireland) as it cooled slower.  Below this is the layered basalts which will form a much more massive block of basalt.  Below this is peridotite.\nChemically speaking oceanic material is basaltic whereas continental is granitic.\nContinental volcanic rocks are a lot less systematic in structure as they just intrude through thick layers of other material although they'll generally have larger crystals and will be lighter in colour.  \nBecause of their increased silica content they're more explosive and so this will be seen by the steeper sides of the volcanoes, pumice (solidified ash), etc.
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It all depends on what your requirements are.  A titanium sponge is NOT superior in many applications.
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Depends what you mean. From a utility point of view, yes it certainly is. Sponges have been made from sponge, from cork and from loofahs. Today most sponges are made form plastic. So by that standard it's a sponge.\n\n\nIn biological terms no, it's not. A sponge is an animal that lives in the sea. A loofah is the dried remnants of a type of squash. It's a vegetable.
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They are different in structure and also in the way that gas exchange occurs. \nIn gills, the water flows in a single direction, and the blood flow in the blood vessels occurs in the opposite direction. Thus optimal gas exchange is achieved (there are good illustrations in textbooks to understand this better). However, to take up oxygen effectively, gills need an enormous surface area, because oxygen is relatively scarce in water. Thus, the gill lamellae are subdivided into smaller lamellae, and these in turn into even smaller projections; these extremely thin laminas are supported in water, but collapse onto each other in air, because of  surface tension and gravity. \nLungs can be of 2 types: the basic model comprises paired sacs, with more or less elaborate inner walls for greater surface area, but also with a surfactant substance that decreases surface tension so that these sacs do not collapse. The air goes in and out of the lungs by way of a single duct, thus there isn't a continuous flow of oxygenated air. Less efficient, but air has so much oxygen that it works anyway. The exception are the lungs of birds, in which the blood vessels are at right angles with respect to air flow, and the latter is continuous and unidirectional. \nAll respiratory surfaces need to be moist, and lungs are no exception. However, in this case the moisture is _inside_ the body, and the body surface is still mostly impermeable. \n\nThird choice... that would be perhaps the tracheae of insects. Aquatic arthropods have lungs of different types, and terrestrial chelicerates do have special gills too. But insects have a different system: ducts that pierce the body wall and project inwards, taking oxygenated air directly to the tissues (no participation of the circulatory system).
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go to howstuffworks.com search for hydralics they've got a great article on them
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Due to differences in chemical structures
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Typing out all the differences would be crazy.\nCheck out the links i've posted below.
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Similarities: They both move down a concentration gradient & they do not need ATP.\n\nDifferences: Osmosis is only for water molecules & it happens through a partially permeable membrane.
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That's a hard one,but I think its Sponge.
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Corals (class Anthozoa), which include sea anemones (order Actiniaria), are gastrovascular marine cnidarians (phylum Cnidaria) existing as small sea anemone-like polyps, typically forming colonies of many individuals. The group includes the important reef builders known as hermatypic corals, found in tropical oceans, and belonging to the subclass Zoantharia of order Scleractinia (formerly Madreporaria). The latter are also known as stony corals in as much as the living tissue thinly covers a skeleton composed of calcium carbonate. A coral "head" is formed of many individual polyps, each polyp only a few millimeters in diameter. The colony of polyps function essentially as a single organism by sharing nutrients via a well developed gastrovascular network, and the polyps are clones, each having the same genetic structure. Each polyp generation grows on the skeletal remains of previous generations, forming a structure that has a shape characteristic of the species, but subject to environmental influences.\n\nAlthough sea anemones can catch fish and other prey items and corals can catch plankton, they obtain much of their nutrient requirement from symbiotic unicellular dinoflagellates (type of algae) called zooxanthellae. Consequently, they are dependent upon growing in sunlight and for that reason usually found not far beneath the surface, although in clear waters corals can grow at depths of 60 m (200 ft). Other corals, notably the cold-water genus Lophelia, do not have associated algae, and can live in much deeper water, with recent finds as deep as 3000 m. Corals breed by spawning, with many corals of the same species in a region releasing gametes simultaneously over a period of one to several nights around a full moon.\n\nCorals are major contributors to the physical structure of coral reefs that develop only in tropical and subtropical waters. Some corals exist in cold waters, such as off the coast of Norway (north to at least 69° 14.24' N) and the Darwin Mounds off western Scotland. The most extensive development of extant coral reef is the Great Barrier Reef off the coast of Queensland, Australia. Indonesia is home to 581 of the world's 793 known coral reef-building coral species.\n\n\n\nHydra is a genus of simple, fresh-water animals possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa.\n\nHydras are low power microscopical life forms and are often studied by biologists due to their regenerative powers. They can be found in most un-polluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas.
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Actually, removing the sponges would cause the sea level to drop (the sponges do take up volume).  Perhaps you could personally remove them with all the spare time you have on your hands.
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Cnidarians live mainly in marine environments. Examples of cnidarians are the jellyfish, sea anemones, and corals. They are different from sponges because sponges have assymmetry which means they have no definite shape. Cnidarians have radial symmetry.
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They have a water vascular system which is unique to echinoderms (sea urchins, sea stars, etc) since they have a digestive system but no circulatory system.  They have an opening called a "madreporite" through which water flows into their bodies.  They have a system of canals within their bodies, and the flow of water transports nutrients.  It is also used for movement and respiration.
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two distinct forms have to be different species... don't really get what you're asking but hope that helps...