2-424: Holasteroida Spatangoida The Atelostomata are a type of sea urchins . They are distinguished from other sea urchins by their irregular shape and the absence of a feeding lantern. The group includes the well known heart urchins , as well as some less familiar and extinct forms. This article about a sea urchin is a stub . You can help Misplaced Pages by expanding it . Holasteroida Holasteroida
4-415: 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
#585414