The larvae are bilaterally symmetrical and have a distinct left and right side (unlike adults of the species, which have a radial symmetry). These larvae have a gut containing internal cilia, which the organism utilizes to inhale and transport food particles, such as diatoms and other microscopic creatures in the plankton.īrachiolaria larvae live as plankton, suspended in the ocean water and moving about by a coordinated motion of the external cilia. Several more weeks into the developmental period, the brachiolaria larval stage is reached. The next stage is the gastrula, followed by differentiation into the bipinnaria larval stage. After the gametes are matched and undergo fertilization, a blastula develops that employs cilia to enable free swimming of the embryo. Starfish may also use chemical signals to initiate the fertilization process. These include the length of the day to indicate the appropriate time of year, and the occurance of dawn or dusk to determine the correct time of day.
In order to increase the chance of fertilization, it is believed that starfish gather in groups when they are ready to spawn, employing several environmental signals to coordinate the timing. A majority of the starfish species disperse exceedingly large numbers of their gametes (eggs and sperm) freely into the water in the hope of an external fertilization event. Larval specimens of the common starfish Asterias rubens (phylum Echinodermata) occur in the plankton among those of sea urchins, sea cucumbers, and brittle stars.
Molecular Expressions: Science, Optics & You - Olympus MIC-D: Brightfield Gallery - Starfish Brachiolaria Larvaīrightfield Digital Image Gallery Starfish Brachiolaria Larva
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