Holasteroida is an order of irregular sea urchins.
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 peripher of the test. The plastron is never amphisternous.
This order seems to have appeared at the lower Cretaceous.
According to World Register of Marine Species :
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 UrechininaFamily Calymnidae Mortensen, 1907Family Carnarechininae Mironov, 1993Family Corystusidae Foster & Philip, 1978Family Plexechinidae Mooi & David, 1996Family Pourtalesiidae A. Agassiz, 1881Family Urechinidae Duncan, 1889Family 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 †
