What is a hydra, and it's functions?
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It is a protrusion from a fungus, if I remember correctly. It is necessary for feeding saprophytically, that is secreting digestive enzymes into food then absorbing the digested food.
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cnidarians have a sac called a gastovascular cavity where digestion occurs. There's only one opening to it that acts as both a mouth and anus.
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Hermatypic corals (the ones that form coral reefs) have symbiotic zooxanthellae (unicellular algae) within their tissues; the algae receive protection and housing from the polyps, and enable them to produce their calcareous exoskeleton.\nThere are sea anemones that attach to the dorsum of crabs, marine snails, etc. Thus the anemone "travels free" and the other animal is protected. \nMany species of small fishes and crustaceans shelter beneath the umbella of some jellyfish (read example at the link).
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they have horns. Look for small antennae at the back of their head too thats a sure sign that they are good freinds. Just keep those bots away from water
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similar structures with different functions...\n\nBats arms and human arms have similar structure, but different function. Bats wings fly and we use our hands for dexterity
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The constellation Hydra has at least 70 stars.  However, only 2 of those stars have apparent magnitudes brighter than 3 (the lower the number, the brighter).
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Why?  Evolution.\n\nWhat purposes do they serve?  (ah, glad you asked...)\n\nThey keep sweat out of our eyes.\nProvide some amount of shade from the sun.\nAre used to communicate emotions through facial expressions.\n\n... and more!\n\nEyebrows!  I love 'em so much, I've got two!
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The mouth, located at the center of one end of the body, opens into a gastrovascular cavity, which is used for digestion and distribution of food; an anus is lacking.\nAn evolutionary advance the Cnidarians have over sponges is extracellular \ndigestion of food. What this means is Cnidarians actually have a special \ngut cavity for digestion of captured food, rather than allowing each cell \nto do it, like a sponge does. All animals from Cnidarians up have kept \nthis feature! It's very important and allows the animal to be much more \nefficient.\n\nCnidarians (and Hydra) have a gut cavity with only a single opening. \nDigestive enzymes are released from the gut wall and help in the break-\ndown of the food. Once the food has been broken up into smaller particles, \ncells from the gut wall start engulfing the bits using the \nprocess "phagocytosis" (the same way an amoeba feeds).\n\nThe incredible thing about Cnidarian digestion is that when they arose, \nthey were the first animal ever to be able to eat and successfully digest \na piece of food LARGER that itself (although only small pieces by small \npieces).
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The mesoglea?  Basically it pulses its body to swim around.\n\nBy the way, jellyfish are fun to play with, assuming you get the kind where the sting doesn't affect humans.  The other kind are decidedly not fun to play with.
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Archamedies. It was originaly a way to pump water.
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Try searching the internet for "the zapper". It's a device that sends small electrical pulses and energy through the body on specific frequencies to eliminate parasites and diseases. I don't know much about it, but I remember hearing about it a few years ago.
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Leeches can help heal skin grafts and restore blood circulation. Their primary function is to drain blood. Pooled blood around a wound can threaten tissue survival.\nLeeches apply the perfect amount of suction to get the blood flowing
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If you mean the water hydra, the answer is right now (http://en.wikipedia.org/wiki/Hydra_%28genus%29).  If you are referring to the Lernaean Hydra, it lived in the days of Hercules in ancient Greece (http://en.wikipedia.org/wiki/Lernaean_Hydra).
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1.Hydrolyzes proteins via pepsin (a protease). \n2.Kills pathogens by dousing them with hydrochloric acid. 3.Stores food during digestion. \n4.Mechanically digests foods a little bit by churning the acid chyme.
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IT IS A VESTIGIAL ORGAN I.E. AN ORGAN THAT DOES NOT HAVE ANY FUNCTION IN OUR BODY BUT HAS SOME FUNCTION IN OUR ANCESTORS BODIES SUCH AS APES AND MONKEYS. IT DOES NOT HAVE TO DO ANYTHING WITH THEIR TAILS BUT DOES WITH THEIR STOMACH.\nEG: IN BIRDS THE NICTATING GLANDS OF EYES PROTECTS THEM FROM WIND WHEN THEY FLY BUT OUR NICTATING GLANDS ARE USELESS,WE INSTEAD HAVE TO USE SUN GLASSES.\nTRUST ME I JUST GAVE MY BIO. EXAM.
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Its functions are to insulate, suppress corona and arcing, and to serve as a coolant.
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It's not to do so much with the useful function; rather how the symetry arises. Each organisn arises from a single cell. The clump of cells becomes a ball, that then flatens out and develops a neural tube (becoming the spine and brain complex). From that, everything fans out. as the neural tube forms by a symetrical folding, so all things from it are symetrical as a mirror image forms or each part.