Class Ophiuroidea + Class Echinoidea + Class Holothuroidea
External ciliary grooves
Ambulacral grooves extend aborally
Sister classes
Common name: brittle stars
Stalked
Arms narrowly connected to calyx
Ambulacral grooves
Endoskeletal plates reduced
Water vascular system
Endoskeletal plates of CaCO3
Endoskeletal plates fused as test
Ambulacral grooves closed
Aboral madreoporite
Common name: Sea Urchin
Common name: Sand dollar
Common name: sea lilies
Arms widely connected to calyx
Common name: sea stars
Common name: sea cucumbers
Pentaradial symmetry
Oral surface faces substrate