†order Orthopsida Mortensen 1942 (sea urchin)
Alternative spelling: Orthopsina
Full reference: T. Mortensen. 1942. New Echinoidea (Camarodonta). Preliminary notice. Videnskabelige Meddelelsar Dansk Naturhistoriske Forening i Kjøbenhavn 106:225-232
Parent taxon: Echinacea according to H. B. Fell and D. L. Pawson 1966
Sister taxa: Arbacioida, Besairecidaris, Bramus, Camarodonta, Crinocidaris, Glyphopneustidae, Plesiocidaroida, Stomopneustoida
Subtaxa: none
Ecology: slow-moving low-level epifaunal grazer