Question

Most appropriate term to designate the life cycle of Obelia is
 A. Neoteny
 B. Metagenesis
 C. Metamorphosis
 D. None of the above

Answer 1

Hint: In a complete life cycle, when an organism goes through alternation of generations between sexual and asexual forms is termed as metagenesis whereas metamorphosis involves in change in forms on habits of an organism during normal development after the completion of embryonic stage..Besides, delayed physiological development of an organism (specially in humans) is called neoteny.

Complete answer:
Obelia sp. (sea fur), a marine, freshwater hydrozoan, belongs to the phylum Chidaria. It is diploblastic having two true tissue layers- an epidermis and a gastrodermis, with a jelly-like substance (mesoglea) which fills the area between two true tissue layers.
Life cycle of Obelia sp. is completed through two distinct stages: polyp stage and medusa stage. The life cycle begins as immobile polyp colonies that contain gonangium, a reproductive unit. Later, gonangium reproduces asexually while releasing medusa. Medusa or jellyfish can go through sexual reproduction releasing eggs and also sperms into the water. This results in the formation of larvae which attach to the ocean floor as new polyps. Hence in complete life cycle, Obelia begins with polyp stage (asexual generation) and then to medusa stage (sexual generation). Thus alternation of generation takes place which is also known as metagenesis.

Hence, (B) Metagenesis is termed to designate the life cycle of Obelia sp.

Note: As metagenesis and metamorphosis are two quite similar terms, sometimes one makes mistakes in choosing between them. So, keeping this in mind, we should have a clear idea between metamorphosis and alternation of generation (metagenesis) and also neoteny i.e. the retention of physical development of an organism.