{{Short description|Group of sea urchins}} {{Automatic taxobox | name = Irregularia | image = Echinocardium_cordatum.jpg | image_caption = ''Echinocardium cordatum'' | fossil_range = {{Fossil range|Lower Jurassic|recent}} | taxon = Irregularia | authority = Latreille, 1825 | subdivision_ranks = Superorders | subdivision = Atelostomata<br> Neognathostomata }}
'''Irregularia''' is an extant infraclass of sea urchins that first appeared in the Lower Jurassic.
== Description and characteristics == These particular sea urchins are distinguished from other sea urchins by their irregular shape: the anus and often even the mouth are at the two poles of the test, creating a bilateral symmetry instead of the classical 5-fold symmetry of echinoderms. The group includes the well known heart urchins, as well as flattened sand dollars, sea biscuits and some other forms. Most of them live inside the sediment, moving in thanks to their particular spines, and feed on its organic fraction.
<gallery style="text-align:center;" mode="packed"> Image:Heart urchin Spatangoida 1380049 Nevit.jpg|{{center|Test of a spatangoid (oral face): the mouth is on the right and the anus on the left.}} Image:Echinocyamus pusillus.jpg|{{center|''Echinocyamus pusillus''. }} Image:Keyhole sand dollar 01.jpg|{{center|Test of a ''Mellita quinquiesperforata''. }} Image:Live Sand Dollar trying to bury itself in beach sand.jpg|{{center|A "sand dollar" in its environment.}} </gallery> <gallery style="text-align:center;" mode="packed"> Image:Clypeaster reticulatus both sides.jpg|{{center|''Clypeaster reticulatus'' (family ''Clypeasteridae'').}} Image:Encope emarginata (Leske, 1778) derivate 2013.jpg|{{center|''Encope emarginata'' (aboral and oral faces) drawn by Ernst Haeckel (1904). }} Image :Clypeaster rosaceus (Linnaeus, 1758) derivate 2013.jpg|{{center|''Clypeaster rosaceus'', ''ibid''. }} Image:Clypeaster aegypticus (inside).JPG|{{center|Many slices of a ''Clypeaster aegypticus'', showing buttresses and pillars.}} </gallery>
== Taxonomy == [[Image:MHNT_-_Hemipneustes_pyrenaicus_-_1.jpg|thumb|upright=0.8|Fossil of an ''Hemipneustes pyrenaicus'' (Holasteroida).]] [[Image:Ruhrmuseum-Ebene-12-Naturkunde3784.jpg|thumb|upright=0.8|Fossil of a ''Conulus subroundatus'' (Echinoneoida).]] [[Image:Scutella subrotunda (Leske, 1778).JPG|thumb|upright=0.8|{{center|Fossil of a ''Scutella subrotunda'' (Clypeasteroida). }}]] [[Image:Echinolampas ovalis M Eocene Civrac-en-Médoc France.JPG|thumb|upright=0.8|''Echinolampas ovalis'', Middle Eocene, Civrac-en-Médoc, France.]] upright=0.8|thumb|''Echinolampas ovalis'', Middle Eocene, Civrac-en-Médoc, France; oral surface. * super-order Atelostomata ** fossil family Acrolusiidae <small> Mintz, 1968</small> † ** fossil family Collyritidae <small> d'Orbigny, 1853</small> † ** fossil family Disasteridae <small> Gras, 1848</small> † ** order Holasteroida ** order Spatangoida ** fossil family Tithoniidae <small> Mintz, 1968</small> † * fossil genus ''Atlasaster'' <small> Lambert, 1931</small> † * fossil family Desorellidae <small> Lambert, 1911a</small> † * order Echinoneoida * fossil family Galeropygidae <small> Lambert, 1911a</small> † * fossil genus ''Grasia''<small> Michelin, 1854</small> † * fossil order Holectypoida † * fossil family Menopygidae <small> Lambert, 1911</small> † * fossil genus ''Mesodiadema''<small> Neumayr, 1889</small> † * super-order Neognathostomata ** familia Apatopygidae <small> Kier, 1962</small> ** fossil family Archiaciidae <small> Cotteau & Triger, 1869</small> † ** order Cassiduloida ** order Clypeasteroida ** fossil family Clypeidae <small> Lambert, 1898</small> † ** fossil family Clypeolampadidae <small> Kier, 1962</small> † ** order Echinolampadoida ** fossil family Nucleolitidae <small> L. Agassiz & Desor, 1847</small> † ** fossil family Pygaulidae <small> Lambert, 1905</small> † ** fossil genus ''Pygolampas''<small> Saucède, Dudicourt & Courville, 2012</small> † * fossil order Oligopygoida <small> Kier, 1967</small> † * fossil family Pygasteridae <small> Lambert, 1900</small> † * fossil family Pygorhytidae <small> Lambert, 1909b</small> †
==References== * {{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|page= 981|isbn= 0-03-056747-5}} * {{cite worms | id = 510499 | db = Echinoidea | title = Irregularia}}
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Category:Sea urchins Category:Taxa named by Pierre André Latreille
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