Irregularia

Irregularia

Irregularia
Temporal range: Lower Jurassic–recent

PreЄ
Є
O
S
D
C
P
T
J
K
Pg
N

Echinocardium cordatum

Scientific classification

Kingdom:
Animalia

Phylum:
Echinodermata

Class:
Echinoidea

Infraclass:
Irregularia
Latreille, 1825

Superorders

Atelostomata
Neognathostomata

Irregularia is an extant infraclass of sea urchins that first appeared in the Lower Jurassic.
Description and characteristics[edit]
These particular sea urchins are distinguished from other sea urchins by their irregular shape : the anus and often even the mouth are no more 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, movin in thanks to their particular spines, and feed on its organic fraction.

Test of a spatangoid (oral face) : the mouth is on the right and the anus on the left.

Echinocyamus pusillus.

Test of a Mellita quinquiesperforata.

A “sand dollar” in its environnement.

Clypeaster reticulatus (family Clypeasteridae).

Encope emarginata (aboral and oral faces) drawn by Ernst Haeckel (1904).

Clypeaster rosaceus, ibid.

Many slices of a Clypeaster aegypticus, showing buttresses and pillars.

Taxonomy[edit]

Fossil of an Hemipneustes pyrenaicus (Holasteroida).

Fossil of a Conulus subroundatus (Echinoneoida).

Fossil of a Scutella subrotunda (Clypeasteroida).

Echinolampas ovalis, Middle Eocene, Civrac-en-Médoc, France.

Echinolampas ovalis, Middle Eocene, Civrac-en-Médoc, France; oral surface.

super-order Atelostomata

fossil family Acrolusiidae Mintz, 1968 †
fossil family Collyritidae d’Orbigny, 1853 †
fossil family Disasteridae Gras, 1848 †
order Holasteroida
order Spatangoida
fossil family Tithoniidae Mintz, 1968 †

fossil genus Atlasaster Lambert, 1931 †
fossil family Desorellidae Lambert, 1911a †
order Echinoneoida
fossil family Galeropygidae Lambert, 1911a †
fossil genus Grasia Michelin, 1854 †
fossil order Holectypoida †
fossil family Menopygidae Lambert, 1911 †
fossil genus Mesodiadema Neumayr, 1889 †
super-order Neognathostomata

familia Apatopygidae Kier, 1962
fossil family Archiaciidae Cotteau & Triger, 1869 †
order Cassiduloida
order Clypeasteroida
fossil family Clypeidae Lam

Comments are closed.