الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Clams are considered one of the favourite seafoods specially for the people who mainly inhabit the cities which located on marine coasts. They have high value of protein and fair amount of calcium and iron. In Egypt, many of the most commercially important are venerid clams.
Veneridae is one of the largest bivalve families, containing over 500 species of clams. The classification within this family has been controversial at least since the 1930s. The characters used for classifying this group still tend to be superficial, focusing on external features, specially those of the shell, which are adapted to their environment.
Recently the morphological characters are evaluated by mapping them onto the resultant phylogenetic tree. All the previous works encourage and through the light on the molecular genetic characters as a valuable insights for phylogenetic studies. Nucleotide sequences characteristically provide high numbers, usually hundreds or even thousands of characters of little but equal complexity. They form data sets independent from morphological data.
Venerids are filter feeders and good indicators for monitoring the pollution in the surrounding environment. They extract the contaminants with the extracting oxygen and food. They can accumulate these contaminants in their bodies much higher than in the surrounding sea water. So attention has been recently drawn to not only the phylogenetic map but also to the goals of genetic ecotoxicology, in particular, the need to relate genotoxicity in individuals to population and community level.
The main goal of this study was collecting different venerids from different habitats and construct genetic maps to follow any genetic variations.
Seven venerid species were recorded in this study, Callista florida, Dosinia radiata, Gafrarium pectinatum, Paphia undulata, Tapes decussatus, Venerupis aureus and Venerupis pullastra. These species classified previously by morphological characters under four subfamilies and six genera. Tapes decussatus was the common species at the different stations. Some venerids which collected from Suez and Ismailia had some shell abnormalities.
The ecological studies revealed that, there are marked differences between stations (Marsa Matrouh, Alexandria, Ismailia and Suez) in the physicochemical parameters of sea water. Also, the heavy metals content in sea water, sediment, soft tissues and shell of the common clam showed marked differences between stations. Marsa Matrouh samples revealed the lowest heavy metals concentrations while Suez had the highest concentrations of Cd, Cu, Fe, Mn, Ni and Pb and Alexandria had the highest concentrations of Co and Zn. The sequence of metals concentrations was, water shell sediment soft tissues for all metals except with Cd was, water sediment shell soft tissues. TPHs concentration in sea water at Suez recorded higher level than that of Ismailia while at Marsa Matrouh and Alexandria, the concentrations were under the limit of chromatography detection.
Veneridae often serve as a first intermediate host for Digenea and play a very important role in the life cycle of several of these platyhelminthes. Tapes decussatus samples which collected