Reproduction and Life Cycle
When food is plentiful, many Hydra reproduce asexually by producing buds in the body wall, which grow to be miniature adults and simply break away when they are mature. When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some Hydra. Swellings in the body wall develop into either a simple ovary or testes. The testes release free-swimming gametes into the water, and these can fertilize the egg in the ovary of another individual. The fertilized eggs secrete a tough outer coating, and, as the adult dies, these resting eggs fall to the bottom of the lake or pond to await better conditions, whereupon they hatch into nymph Hydra. Some, like Hydra circumcincta and Hydra viridissima, are hermaphrodites and may produce both testes and an ovary at the same time.
Many members of the Hydrozoa go through a body change from a polyp to an adult form called a medusa. However, all Hydra, despite being hydrozoans, remain as polyps throughout their lives.
Read more about this topic: Hydra (genus)
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