Smith, Andrew B. Department of Paleontology, Natural History Museum, London, United Kingdom.
A paraphyletic grouping of extinct irregular echinoids, members of which gave rise to the Holaster-oida and Spatangoida in the Lower Cretaceous. Disasteroids have a split apical disc; the posterior two ocular plates and their associated ambulacra are separated from the remainder of the apical disc (and the anterior three ambulacra) by intercalated interambulacral plates. The apical disc became split in the early evolution of this group as a consequence of periproct migration out of the apical disc. Disasteroids have a strong bilateral symmetry. The peristome, which is small and oval and lacks buccal notches, lies toward the anterior of the lower surface. Plastron plating is usually protosternous but in late members can be meridosternous. Tuberculation is fine, dense, and uniform, without regional differentiation. Larger pore pairs, arranged in phyllodes around the mouth, suggest that disasteroids were deposit feeders with penicillate feeding tube feet. Most species probably lived infaunally, though not burrowing deeply.
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