The crab is a kind of animal which we are quite common, they often live in the water.Some of the appearance characteristics of crabs are also prominent, through which they can be easily distinguished.The outside of the crab's body is a very hard shell, which plays an important role in protecting their body and supporting their body.However, they do not have backbones, so they do not rely on backbones to support their bodies.In fact, crabs themselves are invertebrates, so it is well understood that they do not have backbones.Crabs can be distinguished from vertebrates by their lack of vertebrae.
As mentioned above, the crab has no spine.In fact, crabs themselves are invertebrates, not vertebrates.From these two nouns, we can see that the biggest characteristic of vertebrates compared with invertebrates is that invertebrates have no vertebrae, while vertebrates have vertebrae, which are lower than vertebrates, and they do not have the unique advanced structure of vertebrates.
If further subdivided, crabs can be divided into arthropods, and if carefully divided, they can be divided into crustaceans in arthropods.As crustaceans, many of the characteristics of crabs are more prominent, such as their external layer of a relatively hard shell, the shell is generally composed of chitin.This shell can replace the spine to play a part of the support role, so that crabs can move freely.
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