Echinothurioida
| Echinothurioida Temporal range: | |
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| Fire urchin (Asthenosoma varium) | |
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| Superorder: | Echinothuriacea |
| Order: | Echinothurioida Claus, 1880 |
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See text | |
The Echinothurioida are an order of sea urchins in the class Echinoidea. Echinothurioids are distinguished from other sea urchins by the combination of a flexible test and hollow spines. The membrane around the mouth contains only simple plates, in contrast to the more complex mouth parts of their close relatives, the Diadematoida. They are nearly all deepsea dwellers.