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Among the various life cycles of the myriad of forms of life, certainly the Jellyfish (Phylum Cnidaria, Class Scyphozoa) is one of the most extravagant.
They, in fact, represent only the sexual planktonic phase of a small benthic polyp, that during the winter is fixed to the substrate, in the spring produces by gemmation efire, that growing become small jellyfish and that, once grown-up, produce gametes from which then will born the larva.
Too complicated? It ‘s true. Let’s start from the beginning.
From the egg comes a ciliated larva (called planula) that is fixed to the substrate giving rise to a very particular polyp. Once grown, this polyp begins to divide itself transversely (strobilation). Let us imagine a candlestick that upwards forming horizontal rings as if carrying a stack of pans. Every now and then, the higher pan, the last of the stack, comes off and goes swimming: is born an efira that once developed will become a real jellyfish. The adult will reproduce sexually by producing gametes from which the larva will born and the cycle will begin again.
A single polyp can also produce a dozen efire that in two or three months will become adult jellyfishes, in certain species they growth more than 200 times the size of the individual from which they originated.
Photography: Compass Jellyfish (Chrysaora melanaster, Brandt 1838)
