Irregularia

Irregularia

[i‚reg·yə′lar·ē·ə]
(invertebrate zoology)
An artificial assemblage of echinoderms in which the anus and periproct lie outside the apical system, the ambulacral plates remain simple, the primary radioles are hollow, and the rigid test shows some degree of bilateral symmetry.
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References in periodicals archive ?
3) are concentrated in, but not exclusive to, the regular urchins; larvae from representatives of Cidaridae (earliest diverging extant echinoid clade) and Clypeasteridae (earliest diverging extant Irregularia clade) both have PTBs with a high EI.
The clade containing both Stirodonta and Camarodonta is currently considered sister taxon to the Superorder Irregularia, which includes spatangoids (heart urchins) and clypeasteroids (sand dollars) (Smith et al.