The Echinoid Directory

Biology and geological history


Diadematids form a prominent component of shallow water reef communities, living predominantly in the more sheltered backreef and peri-reefal environments. They are epifaunal and can be found out in the open during the day, relying on herding and their long spines for protection. Their diet comprises small benthic organisms scraped off hard substrates or picked up from the sea-floor. Most species live in shallow water settings of less than 40 m, but a few occur in deeper water shelf settings to about 400 m.

Species whose larval development is known are all planktotrophs. Their larvae has a highly characteristic form with just two elongate arms.

Geological history
In the absence of lanterns and spines, the identification of fossil diadematids is extremely difficult. This is because we now know that species traditionally assigned to the Pseudodiadematidae can have test morphologies similar to diadematids but possess keeled teeth and solid spines. The oldest true diadematid that can be currently recognized is late Cretaceous. However, it is fairly certain that the group has a longer history than this and that when some Jurassic regular echinoids become better known they will turn out to belong this family.