Class Sea urchin, Echinoidea "Sea Urchin (Diadematidae) (20 cm)" by CybersamX via Flickr, Creative Commons Attribution.

Class Sea cucumber, Holothuroidea "Another of that sea cucumber" by Pfly via Flickr, Creative Commons Attribution ShareAlike.

Taxonomy:

Class Sea urchin, Echinoidea

S.Class Euechinoidea (Add)
S.Class Perischoechinoidea (Add)

Class Sea cucumber, Holothuroidea

S.Class Apodacea (Add)
S.Class Aspidochirotacea (Add)
S.Class Dendrochirotacea (Add)