plural noun
Cid·​a·​roi·​da | \ ˌsidəˈrȯidə\

Definition of Cidaroida

: the oldest surviving order of sea urchins containing the most primitive of living forms, all lacking peristomial gills and sphaeridia but having an apically located anus — see cidaridae

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History and Etymology for Cidaroida

New Latin, from Cidaris + -oida

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