Soft-bodied organisms
The term "soft-bodied organism" is used to describe animals without skeleton, roughly corresponding to the group Vermes as proposed by Carl von Linné. All animals have muscles, but since muscles can only pull, never push, a number of animals have developed hard parts that the muscles can pull on, commonly called skeletons.[1] Such skeletons may be internal, as in vertebrates, or external, like in arthropods. However, a surprising number of animals groups do very well without hard parts.[2] This include animals like earthworms, jellyfish, tapeworms, squids and an enormous variety of animals from almost every part of the Animal Kingdom.
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[edit] Commonality
Most soft-bodied animals are small, but they do make up the majority of the animal biomass. If we were to stuff all animals on Earth with hard parts in one pile and the soft-bodied ones in another, estimates indicate that the pile of soft-bodied animals would be at least twice the size of the other pile, quite possibly much larger.
[edit] Size
While their lack of a skeleton typically restrict soft-bodied animals' body size on land, but some marine representatives can grow to very large sizes. The heaviest soft-bodied organisms are likely the giant squids, with maximum weight estimated at 275 kilograms (610 lb) for females, while arctic lion's mane jellyfish mat reach comparable sizes.[3][4] The longest animal on record is also thought to be a soft-bodied organism, a 55 metres (180 ft) long bootlace worm, Lineus longissimus found on a Scottish beach 1864.[5] Most soft-bodied organisms are much smaller, even microscopic. The various organisms grouped as mesozoans are typically composed of just a few hundred cells.[2]
[edit] Fossil record
The lack of hard parts in Soft-bodied organisms makes them extremely rare in the fossil record. Accordingly, the evolutionary history of many of the soft-bodied groups are poorly known. The first major find of fossil soft-bodied animals was from the Burgess Shale in Canada.[6] Today, several Burgess shale type faunas are known, but the history of many groups of soft-bodied animals is still poorly understood.
[edit] References
- ^ Marieb, Elaine; Katja Hoehn (2007). Human Anatomy & Physiology (7th ed.). Pearson Benjamin Cummings.
- ^ a b Ruppert, E.E., Fox, R.S., & Barnes, R.D. (2004): Invertebrate Zoology (7 ed.). Brooks / Cole. ISBN 0030259827
- ^ O'Shea, S. 2003. "Giant Squid and Colossal Squid Fact Sheet". The Octopus News Magazine Online.
- ^ "Lion’s Mane Jellyfish - Reference Library". redOrbit. http://www.redorbit.com/education/reference_library/science_1/cnidaria/2582734/lions_mane_jellyfish/index.html. Retrieved 2010-09-03.
- ^ Carwardine, M. 1995. The Guinness Book of Animal Records. Guinness Publishing. p. 232.
- ^ Clarkson, E.N.K. (1993): Invertebrate Palaeontology and Evolution, (3rd edition). Chapman & Hall, ISBN 0-412-47990-7
