Holasteroida is an order of irregular sea urchins.

Characteristics

These irregular sea urchins are characterized by a particularly marked bilateral symmetry, including for the apical system, which is highly elongated. In some contemporary abyssal groups such as Pourtalesiidae, some species are even bottle-shaped. The mouth (peristome) does not contain an Aristotle's lantern. The anus (periproct) has migrated towards the periphery of the test. The plastron is never amphisternous. Image:MHNT - Hemipneustes pyrenaicus - 1.jpg, Fossile of '' Hemipneustes pyrenaicus'' ( Hemipneustidae,

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...

) Image:Echinosigra amphora.jpg, '' Echinosigra amphora'' ( Pourtalesiidae) This order seems to have appeared at the lower

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

List of 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 specialis ...

: * Family Hemipneustidae (Lambert, 1917) † ** genus '' Hemipneustes'' L. Agassiz, 1835 † ** genus '' Medjesia'' Jeffery, 1997 † ** genus '' Opisopneustes'' Gauthier, 1889 † ** genus '' Plesiohemipneustes'' Smith & Wright, 2003 † ** genus '' Toxopatagus'' Pomel, 1883 † * Sub-order Meridosternata (Lovén, 1883) ** Infra-order Cardiasterina † *** Family Cardiasteridae Lambert, 1917 † *** Family Stegasteridae Lambert, 1917f † ** Family Echinocorythidae Wright, 1857 † ** Family Holasteridae Pictet, 1857 † *** Genus '' Salvaster'' Saucède, Dudicourt & Courville, 2012 † ** Infra-order Urechinina *** Family Calymnidae Mortensen, 1907 *** Family Carnarechinidae Mironov, 1993 *** Family Corystusidae Foster & Philip, 1978 *** Family Plexechinidae Mooi & David, 1996 *** Family Pourtalesiidae A. Agassiz, 1881 *** Family Urechinidae Duncan, 1889 * Family Pseudholasteridae (Smith & Jeffery, 2000) † ** genus '' Eoholaster'' Solovjev, 1989 † ** genus '' Giraliaster'' Foster & Philip, 1978 † ** genus '' Pseudholaster'' Pomel, 1883 † ** genus '' Taphraster'' Pomel, 1883 † * Family Stenonasteridae (Lambert, 1922) † ** genus '' Stenonaster'' Lambert, 1922 †

References

Holasteroida
at the

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

* {{echinoidea-stub