Marine Biology

A look at the Lifecycle of a Jellyfish



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"A look at the Lifecycle of a Jellyfish"
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Bell-shaped body and long tentacles, rhythmically opening and closing its body as it appears to drift through the ocean's waters. This image is just one of the cycles a jellyfish passes through in its short yet invaluable lifespan.

Jellyfish are either male or female and reproduce sexually, although the less dominant scyphistomae generation of jellyfish reproduces asexually. Sperm, released by the male jellyfish into the water, swims into the mouth of the female jellyfish allowing for fertilization of the ova. Fertilization may occur inside the female jellies or in brood pouches which form in pits on the oral arms where the eggs have become lodged.

The short-lived planula larva stage occurs once the egg has undergone embryonic development. In this stage, the free-swimming planula larva leaves the mouth or brood pouch and settles onto a firm surface where it develops into a polyp.

The scyphistoma (or polyp) stage of the jellyfish life cycle is sessile, as the cup-shaped polyp remains stationary during this stage. The polyps mouth and tentacles face upwards allowing it to catch passing food. Budding, when the polyp begins reproducing asexually, occurs once the polyp has grown some. Immature jellies called ephyra are produced by budding. The ephyra are tiny free-swimming jellies which grow in size and become medusa.

The medusa stage of the jellyfish life cycle is the adult stage. The adult jellyfish has a bell-shaped body from which tentacles are suspended. Jellies have an incomplete digestive system, lack basic sensory organs and a brain, but have a nervous system that allows them to perceive stimuli and respond quickly. They are slow swimmers and move their body to create a current forcing prey within reach of their tentacles, feeding on the small fish and zooplankton which become caught in the tentacles.

Be it luck or misfortune, the jellyfish accomplishes this complex life cycle in its brief lifespan of two and a half months (six months if it happens to be lucky).

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