THE VARIED ROLES OF SNAILS - National Universities Commission

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(a) Small intestine – Fasciopsis buski – Heterophyes heterophyes – Metagonimus yokogawai – Watsonius watsoni (b) Large intestine – Gastrodiscoides hominis (iii) Respiratory tract – Paragonimus spp. In the snails the miracidia develop into sporocysts followed by two generations of rediae and later (3 months after) give rise to very short tailed cecariae (micro- cercous Xiphidio- cercariae). These emerge from the snail and swim in water and can survive for 24-48 hours. If they find freshwater crabs they enter. The crab species include Potamon, Sesarma, Eiocheir and Sudanonautes or freshwater crayfish – Astacus. They penetrate and encyst in the gills or muscles as metacercariae. The Freshwater crustaceans can probably become infected by ingesting unencysted cercariae in the water or even inside infested snail. The disease is insidious beginning with a non-specific cough that becomes chronic and is productive of blood tinged sputum known as endemic haemoptysis. Patients also experience pleural pain and dyspnoea. Depending upon secondary bacterial infection there may be pneumothorax and pleural adhesion. Lesions in the brain can lead to seizures. (e) Clonorchiasis 84
Clonorchiasis is caused by Clonorchis sinesis. The species was earlier known as Opisthorchis sinensis. Infection due to this parasite is largely confined to Vietnam to Japan (Including Korea, Taiwan, China). It affects about 10 million persons. Humans are the principal definitive hosts, but dogs and other fish eating canines act as reservoir hosts. Two intermediate hosts are required to complete its life cycle, the first being snails and the second is fish. The eggs passed in faeces contain the ciliated miracidia. They do not hatch in water, but only when ingested by suitable species of operculate snails such as Parafoassarulu, Bulimus, Alocinma. The cercariae escape from these snails and swim about in water, waiting to get attached to the second intermediate host, suitable freshwater fish of the carp family. They then shed their tails and encyst under the scales or in the flesh of the fish to become in about 3 weeks the meta cercariae which are the infective stage. Human infection occurs when such a fish is eaten raw or improperly processed. Frozen, dried or pickled fish may act as source of infection. Infection may also occur through fingers or cooking utensils contaminated with the meta cercariae during preparation of fish for cooking (f) Other Trematodes of Medical Importance (i) Dicrocoeliasis: Disease caused by the trematode parasite Dicrocoelium dendriticum 85
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THE VARIED ROLES OF SNAILS (GASTROP
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1820 and twice that in 1930 (Martin
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contributions of snails to human ex
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a.) Production from the wild (wild
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Gastropods I: Terrestrial or Garden
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contracts and expands and this crea
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live on the surface so that they ca
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Many members of the Carrier shell f
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Most bivalves reproduce by laying m
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the snails, what is true of one spe
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principle, is a rasping tongue with
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sculptural defenses against crushin
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Fig. 6: Shells of different freshwa
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ight larval retractor i.e. establis
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(iii) The hypertrophy of the right
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ys two present kidneys 5. Operculum
Page 33 and 34: organs of some species and found si
Page 35 and 36: imperative for the ecosystem dynami
Page 37 and 38: oth of a direct and an indirect nat
Page 39 and 40: females.. Self fertilization is a c
Page 41 and 42: emerges and goes on a binge of repl
Page 43 and 44: of spermatozoa in males or stimulat
Page 45 and 46: d. LIFE CYCLE & LIFE BUDGET SUDIES:
Page 47 and 48: competitively loosely packed. With
Page 49 and 50: digestible vegetable. Tough plants
Page 51 and 52: Birds Various ducks Storks Kites Ot
Page 53 and 54: when mineral ions form chelate comp
Page 55 and 56: produce stress. Thus snail distribu
Page 57 and 58: Protein (g): 16 Availablecarbohydra
Page 59 and 60: or cocoyam, and palm oil or pea nut
Page 61 and 62: 1925, 1931, at Angola and Namibia;
Page 63 and 64: meat with garlic. British species a
Page 65 and 66: 4. Helicinidae 5. Fissurellidae 6.
Page 67 and 68: Helix nucuea Helix aperta Arianta a
Page 69 and 70: Archachatina calachatina marinae Ar
Page 71 and 72: sites in North Africa but are also
Page 73 and 74: infect man or animals. The five pri
Page 75 and 76: Okafor (1989, 1990, and 1992), Ozum
Page 77 and 78: P. aurita P. byronensis Gyraulus G.
Page 79 and 80: one miracidium the potential of pro
Page 81 and 82: In the snail the miracidium metamor
Page 83: While Potadoma and Semisulcospira s
Page 87 and 88: Table 7: Showing a list of trematod
Page 89 and 90: promising and show reduction of pai
Page 91 and 92: memory loss have a devastating cons
Page 93 and 94: acteria. This bacteriostatic activi
Page 95 and 96: The thin, quickly leached soils of
Page 97 and 98: Snails are also pests of crops wher
Page 99 and 100: (f) The management of the snail far
Page 101 and 102: flakes or maize chaffs and mostly g
Page 103 and 104: important that they are separated i
Page 105 and 106: The profit = 1, 800,000 - 30,000 =
Page 107 and 108: designs that are very attractive an
Page 109 and 110: cornuarietis or of flatworms as bio
Page 111 and 112: In few location of the world, snail
Page 113 and 114: damages to crops. So, they must be
Page 115 and 116: 115
Page 117 and 118: The Nigerian Field, 44 (4), 130-144
Page 119 and 120: 19. Asibey, E. O. A. and child, G.
Page 121 and 122: 32. Dei, G. J. S. (1989). Hunting a
Page 123 and 124: J. moll. Studies, 64 (2), 173-181.
Page 125 and 126: 56. Lux moore, R. (1985). Game farm
Page 127 and 128: 69. Okafor, F. C. (1989). Consumpti
Page 129 and 130: Proc. Symposium organized by the Br
Page 131 and 132: Chronicle Nautilus Batavia, 104,278
Page 133 and 134: Achatina fulicaBowdich,1822 Shell s
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Achatina immaculata Lamarck,1822 Sh
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Achatina stuhlmanni von Martens,189
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Columna leai(Tryon, 1866) : São To
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Shells of Gyraulus costulatus 141
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Shells of Biomphalaria pfeifferi 14
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Shells of Lanistes varicus and oper
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147
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Courtesy of Yurii Yashin Courtesy o
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Yurii Yashin Yurii Yashin Yurii Yas
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THE VARIED ROLES OF SNAILS - National Universities Commission

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