Pedinoida is an order of

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

s, containing the single living genus ''

Caenopedina ''Caenopedina'' is a genus of sea urchins of the family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to ...

''. The group was much more diverse during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

, and represents the oldest surviving order of euechinoid sea urchins. They are distinguished from other sea urchins by the presence of a rigid test with

tessellated A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called ''tiles'', with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of ...

plates. While their primary spines are solid, the smaller ones may be hollow, further distinguishing them from the closely related orders Diadematoida and

Echinothurioida 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 plat ...

, which possess only hollow spines.

References

* * Extant Early Triassic first appearances {{echinoidea-stub