Echinoderms
This starfish usually has 6 to 8 arms.
On this picture, there are several individuals. The number of arms varies but is always a multiple of 5.
On a red gorgonian
Its spines inject a powerful venom that makes any sting very painful. The arrangement of the spines illustrates the 5th order symmetry.
Notice the 5th order symmetry of the yellow dots.
Echinoderms come in very different forms but have two common characteristics:
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a calcareous skeleton made of plates or spines present under the skin,
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a fifth order symmetry.
There are 5 large families:
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the starfish, where the 5th order symmetry is usually obvious,
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the sea urchins whose test has this same symmetry,
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the sea cucumbers,
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the brittle stars,
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the crinoids (comatulas).
The blue starfish perfectly illustrates the 5th order symmetry of these animals.