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Abstract Phylum Mollusca is probably the third most successful animal group after the arthropods and the vertebrates. Slugs and snails belong to class Gastropoda, generally characterized by having a distinct head with tentacles and eyes, a broad flattened foot and a dorsal visceral mass at least partly covered by the mantle. Terrestrial slugs have proved to be one of the most successful of all groups of mollusks. The reduction of the shell has lessened the need for calcium salts with the result that slug can live in a wider range of habitats than most snails. Slugs are tolerant of water loss and the compressible and worm–like body allows the animal to squeeze through crevices in the soil in search of shelter. In recent years, slugs have become increasingly important, partly because several species are agricultural and horticultural pests and partly because they have proved to be useful experimental animals, particularly in the field of neurophysiology. Also, slugs are used in drug industry as slug syrup which is used to cure cough and bronchitis by supporting the self-healing forces of the body. Moreover, some slugs and land snails act as intermediate hosts for helminth parasites causing serious diseases to human and domestic animals. To the best of the present author’s knowledge, the knowledge about the Egyptian terrestrial slugs is still fragmentary, and partial information is available about their distribution, their biology, and the ecotoxicological studies of heavy metals on this group. Also, the majority of studies were carried out in lower Egypt but Upper Egypt is completely neglected. So, the present work is an attempt to fulfill this gap and it aims to: 1- Make a survey of different terrestrial slug species inhabiting different types of soil in Assiut governorate, Egypt. 2- Investigate the distribution and the seasonal fluctuations of the common terrestrial slug populations and the effects of some ecological factors which my have influence on terrestrial slug species. 3- Study the life cycle of the common slug. 4- Investigate the seasonal changes of maturation in the hermaphrodite gland of the common slug. 5- Investigate the difference in the accumulation behavior of heavy metals in the terrestrial slug and an isopod species. 6- Study the impact of cadmium on digestive gland cells of the common slug. To achieve the above mentioned goals, random slug samples were collected from different habitats located at Assiut governorate, to make a survey for the different terrestrial slug species. The samples collected included 39 samples, from Assiut governorate. The survey indicated the occurrence of a total number of eight species. All the species recorded belong to one order: Eupulmonata and two families; namely: Limacidae and Agriolimacidae. The first family included two genera: Lehmannia and Limacus while the second family included one genus: Deroceras. Genus Lehmannia included three species namely: L. valentiana, L. marginatus, and L. nyctelia. Genus Limacus included one species: Limax flavus. Four slug species belonged to genus Deroceras, namely: D. laeve, D. panormitanum, D. reticulatum, and D. sturanyi. The recorded species were divided into constancy classes, and it was concluded that the constant slug species was: Deroceras laeve. The accessory species was: Deroceras panormitanum. The accidental slug species included 6 species, namely: Deroceras reticulatum, D. sturanyi, Lehmannia marginatus, L. valentiana, L. nyctelia, and Limax flavus. For quantitative studies: Monthly samples were taken from three main sites, at Al Malgaa, Assiut for a period of one year; extending from April, 2005 till March, 2006. Some ecological factors including air and soil temperatures, pH, water content (Wt.C.), organic matter (Org.M.) were monthly recorded during the period from April 2005 to March 2006, as well as their seasonal fluctuations at the studied sites. Three slug species were found in these main investigated sites. The three species recorded were: Deroceras laeve, Deroceras panormitanum, and Deroceras reticulatum. The diagnostic characters of the collected slug species are illustrated in the investigation. The total number of slug species collected from the three studied sites during the period of investigation (from April 2005 till March 2006) was 192 individuals. from site I, 71 specimens were collected, constituting 36.98% from the total catch. The collected specimens from site II were 78, constituting 40.63%. from site III, 43 specimens were collected, constituting 22.40 %. Deroceras laeve was the most dominant species recorded in the three sites. The study indicated that the highest number of slugs was obtained during spring in all sites. It was observed that, an increase of density occurs from summer to autumn, from autumn to winter and from winter to spring in all sites. The effect of the studied environmental factors on the abundance of the collected slugs was studied and it was concluded that: 1. The densities of D. panormitanum (r= -0.376), (r= - 0.383), (r= -0.403), were negatively correlated with air temperature, soil temperature, and soil pH respectively. 2. The data obtained clearly indicate that there is no noticeable significant correlation between the abundance of D. laeve and D. reticulatum with all studied factors. 3. The interaction of all factors (multiple regression) has highly significant effect on the abundance of D. panormitanum (R= 0.575, P < 0.01). This regression for the other species was not significant. Statistical multivariate analysis of variance (MANOVA) indicated that no significant differences of the abundance of the studied three species at the three investigated sites during the period of investigation were observed. A part of the present study was focused on the common slug species Deroceras laeve since it was the most dominant terrestrial slug species recorded in the three sites. 121 specimens were collected, constituted 63.02% of the total number. The life cycle of this species was studied in laboratory, which will help in controlling this species since it is considered as an agricultural pest. It is considered as an aphally polymorphic species. So, several (mostly two or three) sexual morphs co-occur. It was concluded that, the length of adult specimens ranged between 1.5-3cm. The age of adults laying eggs ranged between 35-83 days. The number of eggs per specimen ranged between 9-57 egg. It was observed that laying eggs occur in clusters during a period of 7-22 days. The age of death recorded ranged between 41-90 days. In the present study, the hermaphrodite gland of the species D. laeve was studied during different seasons of the year to record its state of maturation. It was noticed that, it differs in its structure and developmental stages during different seasons of the year. It reached its maximum maturity in winter and spring and its least maturity state was in summer and autumn. The impact of cadmium on the survival ratios of Deroceras laeve and the isopod Porcellio laevis were studied. It was concluded that, slugs are highly affected by cadmium than isopods. The effect of cadmium on slugs started clearly at 5o μg/g for soil and food treated groups. In case of both treated groups, the effect started at 100 μg/g. The effect of cadmium on isopod of the experimental groups started at 200 μg/g, 400 μg/g and 600. Also, Cadmium concentration and patterns of accumulation in both slug and isopod species were studied in laboratory for three weeks: after 3 weeks of exposure to cadmium through food and/or soil, the Cd concentrations in Deroceras laeve (slug) and Porcellio laevis (isopod) as well as food and soil were measured. Regarding cadmium patterns of accumulation in slug and isopod, the bioaccumulation factors: (BAF) (indicating the ratio of metal concentration in animal to food metal concentration) and bioconcentration factors (BCF) (indicating the ratio of metal concentration in animal to soil metal concentration) were calculated for every treated groups. Overall, cadmium concentrations, BAF and BCF were highly significant in isopod than in slugs. Generally, slugs and isopods showed increased cadmium concentrations in case of metal addition in soil and/or food. Also, the histological structure of the digestive gland of Deroceras laeve using Transmission Electron Microscope was performed to record the role of this gland in the elimination of Cd as a heavy metal. It consists of two unequal lobes, compound tubular and brown in color. Each lope consists of large number of digestive acini bound together by loose connective tissue and are characterized by their thin basal lamina. Moreover, numerous haemocoelic vessels and sinusoids are found between the acini. Digestive gland-acini are lined with simple epithelial cells arranged around a narrow irregular lumen. The lumen of acini usually contains large number of bodies containing vacuoles and food debris. The simple epithelial cells of the digestive gland can be differentiated into two main cell types: digestive cells and calcium cells. A third type of cells, excretory cells thought to be a step in life cycle of digestive cells and another type of thin cells are distributed, apparently at random between the different cells. In an experiment on the slug D. Laeve to test the effect of different Cd concentrations in food and in soil on the cells of digestive gland and to see the role of this gland in the elimination of heavy metals, seven groups were prepared as follows: Group 1: control (without treatment). Group2: treated with 50μg/g cadmium in food. Group3: treated with 50μg/g cadmium in soil. Group4: treated with 50μg/g cadmium in both food and soil. Group5: treated with 400μg/g cadmium in food. Group 6: treated with 400μg/g cadmium in soil. Group7: treated with 400μg/g cadmium in both food and soil. It was concluded that the digestive gland plays an important role in the elimination of heavy metals entering the slug. |