The metamorphosis of an urchin is a transient moment when the floating larva becomes something else

In this video, you see the formation of the urchin rudiment within the body of a late pluteus larva. This is a seasonal event, which massively and synchronously occurs in the North Sea during early April. Plutei are planktonic larvae of sea urchins, and their drifting power helps to find new habitats in the ocean. The floating larva of an urchin and the bottom-dwelling urchin have different morphology and structure reflecting their needs and the purpose. This causes the need for a transition - metamorphosis, when the larval plutei transform into juvenile urchins. These juveniles start as pentameric disks embedded within the bodies of the metamorphic larvae.