The Life Cycle of a Starfish
Starfish are unique animals in that they can reproduce in both sexual and asexual manners. Each starfish is a male or female, but the animal's actual reproductive method will depend solely on what specie of sea star is in question. There are over 1,800 species of starfish, so there is a lot of variety in the creatures' lifecycles.
Fertilization
Starfish release their gametes into the ocean, where they mix with the gametes from a starfish of the opposite sex. To increase chances of fertilization, starfish tend to gather in groups when they are ready to spawn and then they coordinate the timing through environmental signals and chemical signals.
Early Lives
In the embryonic stage, sea star embryos become part of the zooplankton in the sea. After growing beyond fertilized eggs, the creatures grow into first-stage larve known as bipinnaria.
The second-stage larvae are called brachiolaria. These babies are initially bilaterally symmetric, meaning they have a distinct left and right side. In the brachiolaria stage, the larvae survives on a yolk from its egg stage or from eating other types of plankton. They swim by beating their cilia together.
Metamorphosis
When they become large enough, the starfish move to the ocean floor and grow into maturity. This also allows them to transform from bilateral symmetry to radial symmetry, usually revolving around five arms although some species and individuals may have more or less.
Starfish in aquariums have been known to live up to eight years. It is not known how long the average wild sea star will survive, but they may live anywhere between five to 20 years depending on the species.
Reproductive Variations
Some female starfish lay eggs that cling to the surface of their stomach or the ground. The males spawn gametes, which fertilize these eggs, and then the eggs hatch and grow on the ground. These species tend to exist in deep sea and polar environments where plankton larvae would not bode well.
Asexual Reproduction
Some sea stars reproduce asexually by fragmenting off part of an arm that will eventually develop into a completely new sea star. The regeneration can only occur if part of the animal's central ring is included in the severed arm.
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