Compare the life cycle of a jellyfish and a hydra. Identify similarities and difference with respect to medusa stage
The correct answer and explanation is:
The life cycles of both jellyfish and hydra are fascinating examples of cnidarian biology. They both have two distinct stages: the polyp and the medusa, but they differ significantly in their progression through these stages.
Jellyfish Life Cycle:
Jellyfish, or members of the class Scyphozoa, typically begin their life cycle as a fertilized egg that develops into a planula larva. The planula settles on a substrate and develops into a polyp. The polyp then undergoes a process called “strobilation,” in which it produces medusa buds through asexual reproduction. These medusa buds eventually detach from the polyp, growing into the adult medusa stage that is familiar as a jellyfish. This medusa is free-swimming and capable of sexual reproduction, producing gametes that fertilize to form the next generation of planula larvae.
Hydra Life Cycle:
Hydra, part of the class Hydrozoa, is a much simpler cnidarian, and its life cycle differs from jellyfish in that it is primarily in the polyp stage throughout its life. While it can reproduce sexually under certain conditions, it most often reproduces asexually through budding. Hydra does not have a true medusa stage, although some species within the Hydrozoa class do exhibit this stage. When hydra does reproduce sexually, it forms a medusa-like structure, but it is temporary and smaller than the free-swimming medusa of jellyfish. The hydra’s sexual reproduction involves the production of eggs and sperm, which fertilize externally.
Similarities:
- Polyp Stage: Both jellyfish and hydra begin life as polyps.
- Medusa Stage (in Jellyfish): The medusa is a key feature of the jellyfish life cycle and is the adult, free-swimming stage that plays a significant role in sexual reproduction.
Differences:
- Presence of Medusa: The jellyfish has a prominent medusa stage that is a free-swimming adult, while hydra does not have a true medusa stage except for some species in the Hydrozoa class.
- Asexual Reproduction: Jellyfish reproduce asexually through strobilation, whereas hydra mostly reproduce asexually by budding, with sexual reproduction occurring only under specific environmental conditions.
In conclusion, while both organisms share common cnidarian life cycle features, the medusa stage is much more developed and central to the jellyfish life cycle than in hydra, which lacks a prominent medusa form.