Notes on PHYLUM CNIDARIA Or COELENTERATA
This phylum is also known as Coelenterata due to the presence of cavity known as coelenteron. This phylum takes its name due to the presence of cnidocytes, which contain organelles (cnidae) characteristics of the phylum. This phylum has the known species of almost 9000 and in some books, 11000 species are also mentioned. It includes plant like hydroid, jellyfish, sea anemone and coral etc. They may be in the form of a sessile polyp or freely floating medusa. Cnidaria Evolution of the nervous system was first time observed in cnidarians Characteristics of phylum Cnidaria I. Stinging cells called nematocysts housed by cnidocytes are found in the phylum. II. Most are marine but some are also present in fresh water. III. Possess radial or biradial symmetry (modification of radial symmetry). IV. Diploblastic and show tissue level organization. V. Mesoglea which is non-c...