Echinoids remained only a very minor element of the benthos throughout the Palaeozoic and are never common as fossils. Although all had a lantern of some sorts it was not a particularly strong or ...

This is a synapomorphy for the crown group of the Echinoidea, and is also true for all post-Palaeozoic echinoids, bar one, Tiarechinus. By contrast almost all Palaeozoic echinoids have a test which ...