Bothriocidaris

Bothriocidaris is an extinct genus of echinoid from the Ordovician.

It grew to 1.6 centimetres (0.63 in) in size[1] and fed on plankton.

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Bothriocidaris globulus. from the Encyclopædia Britannica, 1911. The short spines which were attached to the tubercles are not drawn.