Crab
From CreationWiki, the encyclopedia of creation science
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Many people are confused about the term crab. When people see Hermit Crabs, King Crabs, and Horseshoe Crabs, they think they are all crabs, but really, none of them are true crabs. Only members of the Brachyura are considered to be true crabs. Despite many similarities, other crabs are not true crabs. Hermit Crabs, King Crabs, and Porcelain Crabs all belong to the Anomura and can be distinguished from true crabs by counting their legs. In Anomura, the last pair of Pereiopods, which are walking legs, are hidden inside the carapace so that only four pairs of legs are visible. Unlike them, true crabs always have five visible pairs of legs, thus they belong to the order Decapoda whose name means "ten feet".
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Anatomy
True crabs are 10 footed (decapod) crustaceans. They have five pairs of walking legs; the first of which are modified into a pair of claws. They typically have a flattened shell. Most crabs, like a raninoida crab, have an abdomen that is folded underneath the cephalothorax.
Their sexes show clear dimorphism, meaning the male and female can be easily distinguished. The abdomen of a male is thinner than that of a female and located under the thorax. Female crabs, however, have a wider abdomen and retains a greater number of pleopods, which is related to the carrying of the fertilized eggs. In those species in which no such dimorphism is found, the position of the gonopores have to be used instead to identify the sexes. Gonopores are on the third pereiopod, or on the sternum in higher crabs. Males have gonopores that are at the base of the fifth pereiopods on the sternum.
Reproduction
Crabs reproduce sexually.
Ecology
Crabs are a very diverse group that are mostly found in saltwater. Only a few live in freshwater or on land near freshwater.
Lack of evolution
Crabs have remained essentially unchanged since their first appearance on earth. Even evolutionists admit they are stumped as to why crabs don't seem to have evolved. In an interview with the late well-known zoologist–biologist Ernst Mayr, Mayr was quoted as saying:
- "In evolutionary biology we have species like horseshoe crabs. The horseshoe crab goes back in the fossil record over two hundred million years without any major changes. So obviously they have a very invariant genome type, right? Wrong, they don't. Study the genotype of a series of horseshoe crabs and you'll find there's a great deal of genetic variation. How come, in spite of all this genetic variation, they haven't changed at all in over two hundred million years while other members of their ecosystem in which they were living two hundred million years ago are either extinct or have developed into something totally different? Why did the horseshoe crabs not change? That's the kind of question that completely stumps us at the present time." [1]
Creationists believe the lack of evidence for crab evolution is because crabs did not evolve. They were created as crabs in the beginning. [2]
Gallery
 Marbled swimming crab |
Related References
- Crab by Wikipedia
- Blue Crab by Blue Crab
- Red King Crab by Noaa
See Also
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