Polyps are tubular body shapes of cnidarians that are attached to a firm surface.
<h3>What are cnidarians?</h3>
Cnidaria or Coelenterata is a phylum of aquatic animals most of which are marine. Any organism under this phylum is called a cnidarian.
These have special cells called cnidocytes (stinging cells) which help to capture prey.
Examples of this group are the corals, jellyfish, hydra, sea anemone.
Cnidarians have two types of body forms the polyp and the medusa which change during the life cycle of the animal. Some have only one type of body form throughout their life.
The polyp is tubular and sessile, usually attached to a firm surface.
Medusa (Jellyfish) is bell shaped and motile having tentacles hanging out at the margins.
Spicules are sharp needle like shapes embedded in the sponges which help in defense.
Nematocysts are large organelles produced as a secretory vessel from Golgi within cells called nematocyte in cnidarians.
The difference between granites and basalts is in silica content and their rates of cooling. A basalt is about 53% SiO2, whereas granite is 73%. Intrusive, slowly cooled inside the crust.
