This animation traces the development of the sea urchin from

the single fertilized cell to

the baby sea urchin.

Some of the steps along the way:

At the forth division the micromeres form

The swimming blastula "hatches"

Gastrulation forms the mouth from the anus

Prism stage. Embryo starts to feed

Early Pluteus, about 3 days from start

Late Pluteus, about one week

Metamorphosis happens at several months

Producing the baby sea urchin