The relationship between metagenesis and polymorphism has raised the question—is metagenesis an outcome of polymorphism or has it lead to the emergence of polymorphism? A discussion on the existence of different grades of metagenesis in cnidarians will help us to find a logical answer. Gradations of Metagenesis: Four different forms of life-histories are seen in the cnidarians which exhibit a [...]
Learn about the comparison between Aurela and Urticina. Comparison # Aurelia: 1. Aurelia is elongated tube-like body with narrow proximal end differentiated into stalk for attachment. 2. Aurelia is about 1.5 cm in height. 3. Distal tentacle: 16 solid tentacles developed in regular order (4 per-radial, 4 inter-radial and 8 ad-radial tentacles). 4. Manubrium is present in Aurelia. 5. Mouth [...]
The following points highlight the two main types of polymorphic variabilities in Siphonophora. 1. Modifications of the Polyp: A. Gastrozooids or Trophozooids or Nutritive Zooids: Characters: 1. It is like a typical polyp (Fig. 12.34A,B). 2. Each gastrozooid is a cylindrical and funnel-shaped body with a large mouth. 3. Presence of a well-formed coelenteron. 4. A single long contractile and [...]