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Abstract Mollusca is the second largest phylum of the animal kingdom, forming a major part of the world fauna. The Gastropoda is the only class of molluscs which have successfully invaded land. They are one of the most diverse groups of animals, both in shape and habit. Among gastropods, land snails (subclass: Pulmonata) are one of the most numerous with almost 35,000 described species of the world. On reviewing literature conducted on land snails of Egypt, as far as can be ascertained, most studies were focused on Lower Egypt but Upper Egypt was neglected. So, the present investigation was designed to fulfill this gap and to promote and enhance the studies of land snails, especially those which have economic importance. The study aims to: 1- Make a survey of different terrestrial snail species inhabiting different types of soil in Assiut governorate, Egypt. 2- Study the horizontal distribution of common terrestrial snail populations in Assiut governorate to make the distribution map. 3- Investigate the seasonal fluctuations of the terrestrial snail populations and effects of some ecological factors (which my have influence on terrestrial snail species) in Assiut city. 4- Study the life cycles of common snails.5- Study the effects of some substrates on certain traits of a common snail. To achieve the above mentioned goals, the following procedures were taken: For qualitative study, random land snail samples were collected from 95 different locations in Assiut governorate, during a period; from April 2007 till October 2008, to make a survey for different terrestrial snail species present. For quantitative studies, four sites from the above mentioned locations were chosen. The first two locations were at Al- Malga, Assiut, these are: Mangoes orchard and Mandarin orange. The third location was a vegetated land at El-Wasta. The fourth location was an ornamental farm of Assiut University. For quantitative studies, monthly samples were taken from the main four studied sites mentioned above, for a period of one year; extending from October 2007 till September 2008. Some ecological factors including air and soil temperatures, relative humidity, percentage of soil water content (%Wt. C.) and percentage of soil organic matter content (%Org. M.), light and soil pH were monthly recorded during the period of study, as well as their seasonal fluctuations at the studied sites. A part of the present study was focused on common snails Monacha obstructa and Oxyloma elegans since they were the most dominant terrestrial snail species recorded in the four sites. The life cycles of these species were studied in laboratory, which will help in controlling these species since they are considered as agricultural pests. Effects of different substrates on certain traits of Oxyloma elegans were studied. The results can be summarized as follows: The survey indicated the occurrence of a total number of nine species. Four species were recorded for the first time in Egypt namely: Pupoides coenopictus, Oxyloma elegans, Vitrea pygmaeum and Cecilioides acicula. All the species recorded belong to order: Pulmonata and include eight families namely: Pupillidae, Vallonidae, Succineidae, Zonitidae, Helicidae, Hygromiidae, Helicodiscidae and Ferussaciidae. The recorded species were divided into constancy classes, and it was concluded that there was no constant snail species. The accessory snails included Oxyloma elegans, Monacha obstructa, and Eobania vermiculata, while the accidental species included Vallonia pulchella, Theba pisana, Helicodiscus singleyanus inermis, Vitrea pygmaea, Pupoides coenopictus and Cecilioides acicula. Four snail species were found in the four main investigated sites. The four species recorded were: Monacha obstructa, Oxyloma elegans, Eobania vermiculata and Theba pisana. The total number of snail species collected from the four studied sites during the period of investigation was 3117 individuals. from site I, 63 specimens were collected, constituting 2.02% from the total catch. The collected specimens from site II were 82, constituting 2.63%. from site III, 1017 specimens were collected, constituting 32.63%. from site IV, 1955 specimens were collected, constituting 62.72%. The study indicated that the highest number of snails (Monacha obstructa, Oxyloma elegans and Theba pisana) was obtained during winter and spring in all sites. In case of Eobania vermiculata the highest number was obtained during summer. The effect of the studied environmental factors on the abundance of the collected snails was studied and it was concluded that: 1. The abundance of Monacha obstructa was positively correlated with percentage of soil water content, percentage of organic matter and soil pH. 2. The abundance of Oxyloma elegans was negatively correlated with air temperature and positively with relative humidity, percentage of soil waster content and pH. 3. The percentage of soil water content was positively correlated with the abundance of Eobania vermiculata and Theba pisana. 4. The total abundance of the four snail species is affected positively by the percentage of soil water content. Studies of the population dynamics of Monacha obstructa and Oxyloma elegans indicated that:In case of O. elegans, the percentage of young snails during different seasons was comparatively low, since it ranged between zero in autumn and 20% in spring. In case of M. obstructa, the percentage of young was comparatively higher in different seasons than that of O. elegans. In M. obstructa, it could be noticed that young flourish in spring (30%) but they reached minimal percentages in summer (7%) and winter (20%). In case of adults of both Monacha obstructa and Oxyloma elegans, it was observed that they were generally present with high percentages during all seasons. The percentages of adults in summer were markedly increased inspite of decreasing the population in general. In case of the percentages of olds of the two studied species, it could be noticed that in Monacha obstructa, this percentage was markedly lower than Oxyloma elegans. Studies of the life cycle of Monacha obstructa and Oxyloma elegans: The study indicated that there were several differences between the two studied species. The lifespan in M. obstructa took about 12 months while in O. elegans it took about 8 months. It was noticed that in Monacha obstructa, laying eggs occurred during two periods. The first period took about six months (from mid-autumn till mid-spring) while the second period took about two weeks at the beginning of autumn. In case of Oxyloma elegans, laying eggs took about 6.5 months, starting from mid-October until the end of May. In the present study, it was recorded either in laboratory or in the field that in Monacha obstructa and Oxyloma elegans eggs are absent during summer months. Also, many traits (14 characters) of Monacha obstructa and Oxyloma elegans were recorded during rearing and concluded that the two species differ in the studied traits. Study the effects of cross fertilization and self fertilization on certain traits of reared Monacha obstructa and Oxyloma elegans: For both investigated species, there were significant differences in the three traits between single and paired individuals, these traits are: 1: No. of clutches laid/snail: there was a marked increase in the paired snails than in single one. This increases the fecundity. 2, 3: Mean egg weight and diameter of egg: there was a marked increase in single individuals than in paired individuals. In case of the trait: mean hatchling size; there was a marked increase in paired snails in Monacha obstructa and the opposite was observed in Oxyloma elegans. Study the effects of substrate on certain traits of Oxyloma elegans: The effects of substrate on certain traits of Oxyloma elegans could be concluded that there are highly significant differences in all the studied traits except in the two traits namely: length of adult and weight of adult. It could be concluded also, that the soil as a substrate, is the most suitable habitat for the snail, followed by leaves. The least suitable substrate was the twigs, since none of eggs hatched in this case and the majority of traits were markedly reduced including length of adult when die, lifespan, no. of clutches laid/snail, mean no. eggs/clutch, no. of eggs/snail, mean egg weight and diameter of egg. |