Cnidarian - Cnidarian - Critical appraisal: The classification of living cnidarians is relatively stable and generally accepted. This is the most venomous group of all the cnidarians (Figure 4). Jellyfish, any planktonic marine member of the class Scyphozoa (phylum Cnidaria), a group of invertebrate animals composed of about 200 described species, or of the class Cubozoa (approximately 20 species). In spite of […] Cnidarians contain specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts (stingers). Classes in the Phylum Cnidaria. Phylum Cnidaria is a pretty cool group of animals. They all have tentacles with stinging cells called nematocysts that they use to capture food. Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers.Nearly all (about 99 percent) cnidarians are marine species. Hydros- water, zoon- animal): Either only polyps are found or polyps and medusae are present. All Cnidaria are aquatic, mostly marine, organisms. This is because cnidarians are things like corals, anemones, jellies, and hydras. A Cnidocyte is … These species may achieve sizes of 15–25 cm. Most Cnidarians have radial symmetry. The phylum Cnidaria contains more than 10,000 living species, among them, mostly are marine animals whereas only 20 species inhabit in freshwater. Characteristics of Chordata. One of the most important distinguishing characteristics of the phylum cnidaria are the Nematocysts. Nematocysts – and their enclosing Cnidocytes – come in about 24 different forms. The relationship between Hydrozoa and Scyphozoa is not very clear. In some groups, some of these are present only during embryonic development. Class Hydrozoa represents the most primitive forms amongst the Cnidarians. Phylum Cnidaria. Nearly all (about 99 percent) cnidarians are marine species. The differences play a functional role in the classification of the phylum. Cnidarian species are found throughout the world and are quite diverse, but they share many similar characteristics. Hydrozoa (Gk. The key difference between Cnidaria and Ctenophora is that the cnidaria show alteration of generation between medusa and polyp, while Ctenophora does not show alteration of generation; only medusa form is present.. Phylum Coelenterata is a subdivision of Kingdom Animalia. Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers. Characteristics of Phylum Cnidaria. is the phylum of animals that contains corals, jellyfish (sea jellies), sea anemones, sea pens, and hydrozoans. It consists of two main phyla Cnidaria and Ctenophora and approximately 15000 species included. ADVERTISEMENTS: In this article we will discuss about the interrelationships between the different classes of phylum Cnidaria. The lowest hydrozoan form is exhibited by Hydra and the hydrula stage of some Hydrozoa. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail (Figure 2). The Cnidaria (Cnidaria spp.) Cubozoans display overall morphological and anatomical characteristics that are similar to those of the scyphozoans. The notable cnidarians include hydras, the corals, Portuguese men-of-war, jellyfish, sea anemones, sea whips, sea pens, and sea fans. Class 1. One unanswered question relates to their evolutionary position among the lower Metazoa (a division of the animal kingdom that includes all phyla except the Protozoa). Cnidarians contain specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts (stingers). When damaged, some cnidarians can regenerate their body parts, making them effectively immortal. 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