Phylum: Echinodermata
Class: Echinoidea
Subclass: Regularia

Pentaradial symmetry
Anus and peristome lie in line
Spine attachments
Five sets of ambulacra

Cast (internal mould of an external mould)

Spine attachments very much larger than for irregular echinoids as they have to hold much larger spines. Spines on regular echinoids are for defence and preventing predation, unlike for irregular echinoids where the spines are for movement in burrows. Watch a video of regular echinoids moving: BBC Wildlife Army of Sea Urchins