Cidaroida is an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

of primitive

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) ...

s, the only living order of the subclass

Perischoechinoidea Perischoechinoidea is a subclass of primitive sea urchins that were abundant in the Palaeozoic seas. However, the great majority of species died out during the Mesozoic, as the more advanced euechinoid sea urchins became common. Today, only a si ...

. All other orders of this subclass, which were even more primitive than the living forms, became extinct 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 Creta ...

Description

Their primary spines are much more widely separated than in other sea urchins, and they have no buccal slits. Other primitive features include relatively simple plates in the

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...

, and the

ambulacral Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea ...

plates continuing as a series across the membrane that surrounds the mouth.

Families

According to

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained by scientific speciali ...

: * family Anisocidaridae Vadet, 1999 † * super-family Cidaridea Gray, 1825 ** family

Cidaridae Cidaridae is a family of sea urchins in the order Cidaroida. Description and characteristics Cidarid sea urchins are characterized by their stout skeleton : the test is thick and hard, with massive perforated tubercles (never crenulated) surr ...

Gray, 1825 ** family

Ctenocidaridae Ctenocidaridae is a family of echinoderms belonging to the order Cidaroida. Genera: * '' Aporocidaris'' Agassiz & Clark, 1907 * '' Ctenocidaris'' Mortensen, 1910 * '' Homalocidaris'' Mortensen, 1928 * ''Notocidaris ''Notocidaris'' is a genus of ...

Mortensen, 1928a ** family Paurocidaridae Vadet, 1999a † * family

Diplocidaridae ''Diplocidaridae'' is an extinct family of sea urchins. These slow-moving low-level epifaunal grazer-omnivores lived in the Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that ...

Gregory, 1900 † * family Heterocidaridae Mortensen, 1934 † * super-family Histocidaroidea Lambert, 1900 ** family

Histocidaridae Histocidaridae is a family 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 d ...

Lambert, 1900 ** family Psychocidaridae Ikeda, 1936 * family Miocidaridae Durham & Melville, 1957 † * family Polycidaridae Vadet, 1988 † * family Rhabdocidaridae Lambert, 1900 † * family Serpianotiaridae Hagdorn, 1995 † * family Triadocidaridae Smith, 1994c † Image:Stylocidaris affinis.jpg, '' Stylocidaris affinis'' (

) Image:Notocidaris.jpg, '' Notocidaris sp.'' (

) Image:Histocidaris variabilis.jpg, ''

Histocidaris variabilis ''Histocidaris'' is a genus of sea urchins in the family Histocidaridae. Some species are known from the fossil record. Species * ''Histocidaris acutispina'' Mortensen, 1927 * ''Histocidaris australiae'' Mortensen, 1928 * '' Histocidaris cari ...

'' (

) Image:Tylocidaris ohshimai.JPG, '' Tylocidaris ohshimai'' ( Psychocidaridae) Image:Miocidaris coaeva MHNT.PAL.2006.94.jpg, '' Miocidaris coaeva'' ( Miocidaridae, fossil) Image:Paracidaris florigemma.JPG, '' Paracidaris florigemma'' ( Polycidaridae, fossil) Image:Cidaris blakei.jpg, ''

Cidaris blakei ''Cidaris blakei'' is a species of sea urchins of the family Cidaridae. Its armour is covered with spines of three types, one unique type being extended and fan-like, making it easily recognized. Alexander Agassiz first described it scientificall ...

'', abyssal Caribbean species Image:Eucidaris tribuloides (Slate-pencil Urchin).jpg, ''

Eucidaris tribuloides ''Eucidaris tribuloides'', the slate pencil urchin, is a species of cidaroid sea urchins that inhabits littoral regions of the Atlantic Ocean. As a member of the basal echinoid order Cidaroida, its morphological, developmental and molecular ge ...

'', shallow Caribbean species Image:Phyllacanthus.jpg, ''

Phyllacanthus imperialis ''Phyllacanthus imperialis'', also known as the Sputnik urchin, imperial lance urchin, imperial sea urchin, imperial urchin, pencil sea urchin, lance urchin, knobby sputnik sea urchin, mine urchin, and land mine sea urchin, is a species of sea ur ...

'', shallow Indo-Pacific species Image:Plococidaris verticillata.jpg, ''

Plococidaris verticillata ''Plococidaris'' is a monotypic genus of echinoderms belonging to the family Cidaridae. The only species is ''Plococidaris verticillata''. The species is found in Malesia Malesia is a biogeographical region straddling the Equator and the ...

'', rare shallow Indo-Pacific species Image:Prionocidaris baculosa.jpg, ''

Prionocidaris baculosa ''Prionocidaris'' is a genus of echinoderms belonging to the family Cidaridae. The genus has almost cosmopolitan distribution. Species: *'' Prionocidaris anacachoensis'' *'' Prionocidaris australis'' *''Prionocidaris baculosa'' *'' Prionoc ...

'', from Philippines Image:Reef0228.jpg, ''

Chondrocidaris gigantea ''Chondrocidaris gigantea'' is a species of sea urchin of the family Cidaridae. Their armour is covered with spines. ''Chondrocidaris gigantea'' was first scientifically described in 1863 by Alexander Agassiz.Kroh, A. (2010). ''Chondrocidaris gi ...

'', from Hawaii

References

Citations

Sources

* * * Cisuralian first appearances Extant Permian first appearances {{echinoidea-stub