THE VARIED ROLES OF SNAILS - National Universities Commission

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B. tropicus B. reticulatus Oxyloma O. elegans Bithynia B. tentaculata Para P. manchouricus fossarulus Ferrisia F. ebunensis Succinea S. putris Cerithidea Cerithidea sp Segmentina S. angustus Physa P. waterloti Pironella Pironella sp Oncomelania O. anadrasi O. hupensis O. nosophora o. lindoensis O. formosana O. chiui Tricula T. aperta S. mekongi The intra-molluscan schistosome larvae are of no direct clinical importance, certain features are of interest. As the miracidium penetrates the snail, the tegumental plates, and cilia are shed and the rest of the body reorganizes into a sac of reproductive cells which absorbs nutrients from the snail tissues known as the mother sporocyst. The daughter sporocysts have even greater nutritional requirements which are best met in the digestive glands and gonads of the snail to which they migrate before beginning full development. The most important aspect of infection in the snail is the massive asexual multiplication which allows 78
one miracidium the potential of producing many thousand cercariae which, when released from the secondary sporocysts, migrate through the tissues into the blood sinuses and escape from the snail through the walls of the superficial blood vessels of the mantle, gill or pseudobrach. The net result of prolonged production of cercariae increases the chance that one cercaria will eventually infect man or other suitable hosts. It is important to note that the snails do not accept infection entirely passively (Loker et al., 1984). Amoebocytic cells originating from the heart epithelium attack invading foreign bodies, possibly in conjunction with soluble factors which themselves are derived from the amoebocytes. This reaction helps to destroy many primary sporocysts within a few days of penetration. In many snail species, the young snails are susceptible, but progressive changes in the composition of the haemolymph result in increasing resistance with age (Michelson, 1986). It is further important to note that some cercariae migrating through the snail tissues are trapped and destroyed in granulomatous reactions. These infection processes of the snail borne trematodes can be broadly divided into oral and(or) transdermal routes of the worms’ larval stages which have been previously released from the infected snails. During development within the human body clinical cymptoms appear. These symptoms include uticaria, fever, ascites, haematemesis, carcinoma and hepatosplenomegaly. After maturation and depending upon the species of infection, the resultant adult worms reside within the blood vasculature system or internal body cavities of the human hosts. Unlike 79
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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
Page 27 and 28: ight larval retractor i.e. establis
Page 29 and 30: (iii) The hypertrophy of the right
Page 31 and 32: 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: P. aurita P. byronensis Gyraulus G.
Page 81 and 82: In the snail the miracidium metamor
Page 83 and 84: While Potadoma and Semisulcospira s
Page 85 and 86: Clonorchiasis is caused by Clonorch
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
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Chronicle Nautilus Batavia, 104,278
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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
Page 151 and 152:
Yurii Yashin Yurii Yashin Yurii Yas
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