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Question
This life cycle belongs to which animal?
This life cycle belongs to which animal?
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Solution
The correct option is A Obelia
This life cycle belongs to Obelia.The free-swimming planula stage of Obelia helps in the dispersal of the species. The life history can be represented as male and female gametes → zygote → planula larva → hydrula → colony → sexual medusae → gametes → zygote and so on.Fertilisation usually takes place in open sea water and here, the gametes are set free. Sometimes, the sperms are carried into the female medusae with water currents and there they fertilize the eggs in situ. However, the parent medusae die soon after liberating their respective gametes.
Development:
The zygote undergoes complete or holoblastic (equal) cleavage to form a single-layered blastula with a blastocoele. Some cells migrate into blastocoele, eventually filling it completely to form a solid gastrula known as stereo gastrula. Its outer cell layer becomes the ectoderm and inner cell mass the endoderm.
The gastrula elongates and its outer layer of ectoderm cells becomes ciliated, and now it is called planula. Soon, a cavity called enteron develops in the solid endodermal cell mass by the process of delamination and the planula becomes a two-layered larva having an outer ciliated ectodermal cells and an inner layer of endodermal cells.
The planula after a short free-swimming existence settles on some solid object by its broader end. The free end forms a manubrium with a mouth and a circlet of tentacles. Thus, a simple polyp or hydrula is formed which grows a hydrorhiza from its base, from which an Obelia colony is formed by budding.
This life cycle belongs to Obelia.
The free-swimming planula stage of Obelia helps in the dispersal of the species. The life history can be represented as male and female gametes → zygote → planula larva → hydrula → colony → sexual medusae → gametes → zygote and so on.
Fertilisation usually takes place in open sea water and here, the gametes are set free. Sometimes, the sperms are carried into the female medusae with water currents and there they fertilize the eggs in situ. However, the parent medusae die soon after liberating their respective gametes.
Development:
The zygote undergoes complete or holoblastic (equal) cleavage to form a single-layered blastula with a blastocoele. Some cells migrate into blastocoele, eventually filling it completely to form a solid gastrula known as stereo gastrula. Its outer cell layer becomes the ectoderm and inner cell mass the endoderm.
The gastrula elongates and its outer layer of ectoderm cells becomes ciliated, and now it is called planula. Soon, a cavity called enteron develops in the solid endodermal cell mass by the process of delamination and the planula becomes a two-layered larva having an outer ciliated ectodermal cells and an inner layer of endodermal cells.
The planula after a short free-swimming existence settles on some solid object by its broader end. The free end forms a manubrium with a mouth and a circlet of tentacles. Thus, a simple polyp or hydrula is formed which grows a hydrorhiza from its base, from which an Obelia colony is formed by budding.
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