The Diadematoida are an order of sea urchins. They are distinguished from other sea urchins by the fact that their spines are hollow, or at best have an open mesh at the core, and by the presence of 10 buccal plates around the mouth. Their tests can be either solid or flexible.

Diadematoida. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Diadematoida.

The Diadematidae are a family of sea urchins. Their tests are either rigid or flexible and their spines are long and hollow.

Astropyga Gray, 1825

Astropyga radiata (Leske, 1778), extant

Diadematidae. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Diadematidae.