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 periphery of the test. The plastron is never amphisternous.[1]
Fossile of Hemipneustes pyrenaicus (Hemipneustidae, Maastrichtian)
This order seems to have appeared at the lower Cretaceous.[1]
According to World Register of Marine Species :
Holasteroida is an order of irregular sea urchins.