Development of Sea Urchin Larvae

Fertilization

• Sea urchins fertilize independently of intercourse, instead releasing eggs and sperm under conditions that promote fertility. In some cases, eggs are able to develop without being fertilized.

Early Development

• The early development of the fertilized egg produces a blastula, which is a small cluster of cells surrounding a hollow space called the blastocoel. The urchin looks like a small ball. This stage takes a few hours to reach after fertilization.

Gastrula

• The gastrula is formed next; this occurs after a process in which cell division happens more rapidly, and a sheet of cells forms to create what will become the sea urchin's interior organs. The mouth and anus appear at this stage, which lasts for several days, and the sea urchin's body elongates slightly.

Archenteron

• The archenteron, the future site of the animal's organs, forms the mesoderm and endoderm. The endoderm lines the sea urchin's internal organs, while the mesoderm will become the spines, reproductive organs and muscles. At this stage, the larva has two "arms" used to gather food and move through the water. This stage lasts several weeks, until the sea urchin is ready to undergo metamorphosis.

Time Frame

• A month after fertilization, sea urchins undergo metamorphosis and attain their adult form. While the sea urchin is still small, no more major changes except in size will occur. This metamorphosis marks the end of the larval stage.