The Phymosomatoida are 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, found in Europe, North America, North Africa and the Middle East. They are distinguished from other sea urchins by the presence of large fused plates on top of the feeding lantern. The test is usually sculpted to some degree, but, unlike their close relatives the

Temnopleuroida Temnopleuridea is an infraorder of sea urchins in the order Camarodonta. They are distinguished from other sea urchins by the presence of large fused plates on top of the feeding lantern. The test is usually sculpted to some degree, and has per ...

, the tubercles are never perforated. The opening in the test through which the anus passes, known as the

periproct The periproct is the final body segment in annelid worms. The anus is located on this segment. The term also refers to the small region surrounding the anus of the sea urchin. See also *Prostomium *Earthworm *Sea urchin Sea urchins () are s ...

, is unusually large in sea urchins from this group. The apical disc, around the mouth, is only loosely attached to the rest of the test and is often missing in fossil species, giving the false impression that they also have a large oral opening.

References

* * Extant Early Jurassic first appearances {{Echinoidea-stub