The genital plate 5, which may collapse in the periproct, is not always visible. |
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The supplementary plates are more and more developed whereas the distance between the periproct and ocular plates increases. |
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On the upper surface, opposite the mouth, is the periproct, which surrounds the anus. |
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The periproct contains a variable number of hard plates, depending on species, one of which contains the madreporite. |
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