during alteration of generation in obelia which one of following give rise to colony
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Answer:
During alternation of generation in Obelia, colonial structure is formed like follows:-
Obelia colony consists of a horizontally branching root-like stolon or hydrorhiza from which emerge many vertical branching stems called hydrocaulus. Branches emerging from the stem terminate either in nutritive zooids, called the polyps or hydranths or in reproductive zooids called blastostyles or gonangia, which produce medusa. Thus, Obelia colony is trimorphic, exhibiting two types of zooids attached to the sedentary colony and a free swimming zooid or medusa.
The colony is made of an inner, tubular and living tissue, the coenosarc, which encloses a canal, called the gastrovascular cavity, whose walls consist of two layers, an outer epidermis and an inner gasrodermis and a gelatinous mesogloea in between. Coenosarc is surrounded externally by a yellowish or brownish, non-living chitinous layer, called perisarc that protects the colony and serves as an exoskeleton. Annuli on perisarc permit limited swaying movements and bending of the zooids.