EduF83 Regular Echinoid (Sea Urchin)

3D Model

Echinoid (Sea Urchin, Hemicidaris sp.)

39×39×27mm

Cretaceous (145-66Ma)

Echinoids are echinoderms, related to starfish and sea lilies. Although this genus is extinct, this fossil closely resembles the shell, or test, of a modern sea urchin. Their long spines fall off quickly after death and hence often fossilise separately from the test. The test of sea urchins are distinctive due to their 5-fold symmetry. The large bumps on the surface, called tubercles, are where the spines attach, and the lines of tiny holes between the tubercles, called ambulacral pores, are where the tube feet, used to move, eat and breathe, come out from.

This genus of urchin has especially large tubercles for the attachment of massive club-shaped spines, comparable to the pencil urchins that still exist today. Such thick spines were effective in blocking attacks by predators.

See: EduF42, EduF88 Irregular Echinoids