Eucidaris metularia is a primitive species of sea urchin and comes from an ancient lineage that has hardly changed over the past 150 million years. The test is robust and somewhat flattened and up to 3 cm (1.2 in) in diameter. The ambulacra are almost straight and have horizontal pairs of pores. The primary spines are few in number, stout with a truncated tip and distinctively banded. The secondary spines surround the primaries and are more numerous, much smaller and flattened. Sea urchins release their gametes into the sea where external fertilization takes place. The larvae are planktonic and drift with the currents. The larvae of Eucidaris metularia and other members of the genus Eucidaris have distinctive fleshy lobes which enables them to be distinguished from other echinoid larvae. At metamorphosis, which takes place after the larvae have settled on the seabed, the rearrangement of tissues is much less extensive in these primitive species than is the case in more advanced echinoids. Learn more about Ten-Lined Urchin