Sea stars shed their eggs and sperm into the water, and fertilization occurs externally, producing a swimming, bilaterally symmetrical larva. The larva settles and undergoes a sessile (attached) period while metamorphosing into the free-living, radially symmetrical adult form. A single female may produce over 2 million eggs in one spawn, but the eggs and larvae form part of the plankton on which many marine animals feed, and few survive.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.