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World Applied Programming, Vol (3), Issue (3), March 2013. 113-115 ISSN: 2222-2510 ©2013 WAP journal. www.waprogramming.com Taking a Brief Look to the Phylum Cnidaria Hamed Nosrati * Masoud Nosrati Ronak Karimi Kamran Malekian Eslamabad-E-Gharb branch, Islamic Azad University, Eslamabad-E-Gharb, Iran. [email protected] Eslamabad-E-Gharb branch, Islamic Azad University, Eslamabad-E-Gharb, Iran. [email protected] Eslamabad-E-Gharb branch, Islamic Azad University, Eslamabad-E-Gharb, Iran. [email protected] Eslamabad-E-Gharb branch, Islamic Azad University, Eslamabad-E-Gharb, Iran. Abstract: The phylum Cnidaria has been investigated in this paper. Cnidarians form an animal phylum that is more complex than sponges. Adult cnidarians appear as either swimming medusae or sessile polyps. They have a supporting structure named, mesoglea. Cnidaria have no brains or central nervous systems. All cnidaria can regenerate. Regeneration is akind of asexual reproduction. In this phylum sexual reproduction often involves a complex life cycle with both polyp and medusa stages. There are no respiratory organs in these animals. Locomotion of these animals has been investigated in this paper. Keywords: Some characteristics of the phylum Cnidaria, Polyp and medusae forms, Regeneration as asexual reproduction in cnidarians I. INTRODUCTION In this paper we will investigate some characteristics of the phylum Cnidaria. In section 2 we will discuss about cnidarians as an animal phylum that is more complex than sponges. Section 3 is about the forms of their body. In section 4 we will discuss about skeletons of these animals. In section 5 we will investigate their locomotion. Section 6 is dedicated to cnidarians' nervous system. Cnidaria have no brains or central nervous systems. Section 7 is about their reproduction. In this section we will discuss about regeneration as asexual reproduction in cnidarians and we will also study sexual reproduction in this animal phylum. We will discuss about respiration n section 8. We will understand that there are no respiratory organs in these animals by studying this section. At the end of paper conclusion is placed. II. ABOUT PHYLUM CNIDARIA Cnidarians form an animal phylum that is more complex than sponges, about as complex as ctenophores (comb jellies), and less complex than bilaterians, which include almost all other animals. However, both cnidarians and ctenophores are more complex than sponges as they have: cells bound by inter-cell connections and carpet-like basement membranes; muscles; nervous systems; and some have sensory organs. Cnidarians are distinguished from all other animals by having cnidocytes that fire like harpoons and are used mainly to capture prey but also as anchors in some species. [1] Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians; more complex animals have three main cell layers and no intermediate jellylike layer. Hence, cnidarians and ctenophores have traditionally been labelled diploblastic, along with sponges. [1][2] However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer. [3] As a result some recent text books classify ctenophores as triploblastic, [4] and it has been suggested that cnidarians evolved from triploblastic ancestors. [3] 113 Hamed Nosrati et al. World Applied Programming, Vol (3), No (3), March 2013. III. BODY FORMS Adult cnidarians appear as either swimming medusae or sessile polyps. Both are radially symmetrical, like a wheel and a tube respectively. Since these animals have no heads, their ends are described as "oral" (nearest the mouth) and "aboral" (furthest from the mouth). Most have fringes of tentacles equipped with cnidocytes around their edges, and medusae generally have an inner ring of tentacles around the mouth. The mesoglea of polyps is usually thin and often soft, but that of medusae is usually thick and springy, so that it returns to its original shape after muscles around the edge have contracted to squeeze water out, enabling medusae to swim by a sort of jet propulsion. [2] IV. SKELETONS In medusae the only supporting structure is the mesoglea. Hydra and most sea anemones close their mouths when they are not feeding, and the water in the digestive cavity then acts as a hydrostatic skeleton, rather like a water-filled balloon. Other polyps such as Tubularia use columns of water-filled cells for support. Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, rather like sponges. [2] In some colonial polyps a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps. Stony corals secrete massive calcium carbonate exoskeletons. A few polyps collect materials such as sand grains and shell fragments, which they attach to their outsides. Some colonial sea anemones stiffen the mesoglea with sediment particles. [2] V. LOCOMOTION Medusae swim by a form of jet propulsion: muscles, especially inside the rim of the bell, squeeze water out of the cavity inside the bell, and the springiness of the mesoglea powers the recovery stroke. Since the tissue layers are very thin, they provide too little power to swim against currents and just enough to control movement within currents. [2] Hydras and some sea anemones can move slowly over rocks and sea or stream beds by various means: creeping like snails, crawling like inchworms, or by somersaulting. A few can swim clumsily by waggling their bases. [2] VI. NERVOUS SYSTEM Cnidaria have no brains or even central nervous systems. Instead they have decentralized nerve nets consisting of: sensory neurons that generate signals in response to various types of stimulus, such as odors; motor neurons that tell muscles to contract; all connected by "cobwebs" of intermediate neurons. As well as forming the "signal cables", intermediate neurons also form ganglia that act as local coordination centers. The cilia of the cnidocytes detect physical contact. Nerves inform cnidocytes when odors from prey or attackers are detected and when neighbouring cnidocytes fire. Most of the communications between nerve cells are via chemical synapses, small gaps across which chemicals flow. As this process is too slow to ensure that the muscles round the rim of a medusa's bell contract simultaneously in swimming the neurons which control this communicate by much faster electrical signals across gap junctions. [2] Medusae and complex swimming colonies such as siphonophores and chondrophores sense tilt and acceleration by means of statocysts, chambers lined with hairs which detect the movements of internal mineral grains called statoliths. If the body tilts in the wrong direction, the animal rights itself by increasing the strength of the swimming movements on the side that is too low. Most species have ocelli ("simple eyes"), which can detect sources of light. However the agile Box Jellyfish are unique among Medusae because they possess four kinds of true eyes that have retinas, corneas and lenses. [5] Although the eyes probably do not form images, Cubozoa can clearly distinguish the direction from which light is coming as well as negotiate around solid-colored objects. [1][5] 114 Hamed Nosrati et al. World Applied Programming, Vol (3), No (3), March 2013. VII. REPRODUCTION In this section we will investigate asexual and sexual reproduction in cnidarians. 7.1 Asexual reproduction All known cnidaria can reproduce asexually by various means, in addition to regenerating after being fragmented. Hydrozoan polyps only bud, while the medusae of some hydrozoans can divide down the middle. Scyphozoan polyps can both bud and split down the middle. In addition to both of these methods, Anthozoa can split horizontally just above the base. [1][2] 7.1.1 Regeneration All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Medusae have limited ability to regenerate, but polyps can do so from small pieces or even collections of separated cells. This enables corals to recover even after apparently being destroyed by predators. [1] 7.2 Sexual reproduction In the Cnidaria sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example in Scyphozoa (jellyfish) and Cubozoa (box jellies) a larva swims until it finds a good site, and then becomes a polyp. This grows normally but then absorbs its tentacles and splits horizontally into a series of disks that become juvenile medusae, a process called strobilation. The juveniles swim off and slowly grow to maturity, while the polyp re-grows and may continue strobilating periodically. The adults have gonads in the gastroderm, and these release ova and sperm into the water in the breeding season. [1][2] VIII. RESPIRATION There are no respiratory organs, and both cell layers absorb oxygen from and expel carbon dioxide into the surrounding water. When the water in the digestive cavity becomes stale it must be replaced, and nutrients that have not been absorbed will be expelled with it. Some Anthozoa have ciliated grooves on their tentacles, allowing them to pump water out of and into the digestive cavity without opening the mouth. This improves respiration after feeding and allows these animals, which use the cavity as a hydrostatic skeleton, to control the water pressure in the cavity without expelling undigested food. [1] Cnidaria that carry photosynthetic symbionts may have the opposite problem, an excess of oxygen, which may prove toxic. The animals produce large quantities of antioxidants to neutralize the excess oxygen. [1] IX. CONCLUSION In this paper we investigated some characteristics of the phylum Cnidaria as an animal phylum. We discussed about their body forms. We studied about cnidarians' skeletons and we also studied about their locomotion, nervous system and respiration. In this paper we investigated cnidarians' reproduction too. We discussed about cnidarians' sexual and asexual reproduction in this paper. REFERENCES [1] [2] [3] [4] [5] Hinde, R.T., (1998). "The Cnidaria and Ctenophora". In Anderson, D.T.,. Invertebrate Zoology. Oxford University Press. pp. 28–57. ISBN 019-551368-1. Ruppert, E.E., Fox, R.S., and Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 111–124. ISBN 0-03-025982-7. Seipel, K., and Schmid, V. (June 2005). "Evolution of striated muscle: Jellyfish and the origin of triploblasty". Developmental Biology 282 (1): 14–26. doi:10.1016/j.ydbio.2005.03.032. PMID 15936326. Ruppert, E.E., Fox, R.S., and Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 182–195. ISBN 0-03-025982-7. "Jellyfish Have Human-Like Eyes". www.livescience.com. April,1 2007. Retrieved 2012-06-12. 115