Cassiduloida is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

s. The group was extremely diverse with many families and species during the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

, but today, only seven extant species remain. A 2019 phylogenetic systematics study by Souto et al. presented a revised classification of the cassiduloids, and hypothesised that the order probably originated in the Early Cretaceous.

Description and characteristics

Cassiduloids have a rounded or slightly oval appearance, and look somewhat similar to heart urchins, although they are actually more closely related to the sand dollars. They are distinguished from other sea urchins by the presence of smaller intervening areas between the main ambulacral areas on the oral surface. They have no lantern as adults, and the petaloids are poorly developed or absent.

List of families and genera

* family Cassidulidae L. Agassiz and Desor, 1847 ** genus '' Cassidulus'' Lamarck, 1801 ** genus '' Paralampas'' Duncan & Sladen, 1882 ** genus '' Rhyncholampas'' Agassiz, 1869 * family Eurhodiidae Souto et al., 2019 ** genus '' Australanthus'' Bittner, 1892 ** genus '' Eurhodia'' d'Archiac & Haime, 1853 ** genus '' Glossaster'' Lambert, 1918 ** genus '' Kassandrina'' Souto & Martins, 2018 * family Faujasiidae Lambert, 1905 * family Neolampadidae Lambert, 1918 * family Pliolampadidae Kier, 1962 † * family Galeropygidae Lambert, 1911 † ** genus '' Galeropygus'' Kier (1962) † ** genus '' Eogaleropygus'' Kier (1962) †

References

* * * Echinoderm orders {{echinoidea-stub