Diadematoida

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.

The Micropygidae form a family of sea urchins within the Diadematoida order of echinoderms. The family contains two living species of the genus Micropyga and one, Kierechinus, known only from fossils. Morphologically, they are quite flat and have short, sharp spines, which are close to each other. They occur in the Indian and Pacific Oceans.

Lissodiadema is the only genus in the family Lissodiadematidae.