RADIATE ANIMALS - PDF

RADIATE ANIMALS There are different types of body symmetry in the animal kingdom, e.g. radial symmetry, bilateral symmetry and pentaradial symmetry. Animals with radial symmetry are known as radiate animals. In radiate animals, the body parts are arranged symmetrically around a central axis....

RADIATE ANIMALS There are different types of body symmetry in the animal kingdom, e.g. radial symmetry, bilateral symmetry and pentaradial symmetry. Animals with radial symmetry are known as radiate animals. In radiate animals, the body parts are arranged symmetrically around a central axis. Radiate animals include the Phylum Cnidaria/Coelenterata and the Phylum Ctenophora. Phylum Cnidaria Members possess radial or biradial symmetry. Biradial symmetry is a modification of radial symmetry such that a single plane passes through the central axis and divides the animals into mirror images. Being radially symmetrical, they have no anterior or posterior ends. Rather, the terms of direction in this phylum are based on the position of the mouth opening. The end of the animal’s body that contains the mouth is the oral end, while the opposite end is the aboral end. Phylum Cnidaria (Cont’d) One distinguishing feature of the cnidarians is the presence of special features known as nematocysts on their body wall. Nematocysts are used for feeding (food gathering) and defence. Another distinguishing characteristic of cnidarians is the alternation of generations in their life hsitories. Alternation of generations means the possession of two body forms, namely polyp and medusa. Polyp is the asexual sessile form of cnidarians Medusa is the sexual and free-swimming form of cnidarians. Classification of the Phylum Cnidaria Class Hydrozoa, e.g. Hydra, Obelia Class Scyphozoa, e.g. Aurelia Class Anthozoa, e.g. Anemones and corals Class Cubozoa, e.g. Chironex