Concentrations of some heavy metals and trace elements such as Cr, Ga, Ni, Zn, Mo, Cu, Pb, Yb, Y, Nb, Ti, Sr, Ba, Mn, Sc, Co, V, Zr, Fe, Al, W, Se, Bi, Sb, As, Cd in recent mollusk shells and factors affecting their distribution and deposits collected from various depths in the southern and southwestern parts of the Marmara Sea are investigated. The distribution of the elements in the shells is categorized into four groups. Of these, concentrations of 12 elements (As, Bi, Cd, Co, Ga, Mo, Nb, Sb, Se, Sc, W and Yb) are below zero [(0.053–0.79)′10?6]; concentrations of seven elements (Cr, Ni, Pb, V, Y, Zr and Cu) are (1.0–6.0)′10?6; concentrations of four elements (Ti, Mn, Ba and Zn) are 10–20′10?6; and concentrations of five elements (Si, Al, Fe, Mg and Sr) are (47.44–268.11)′10?6. The taxonomic characteristics of the 29 elements were studied separately in mollusk shells such as Chamalea gallina (Linné), Pitar rudis (Poli), Nassarius reticulatus (Linné), Venerupis senescens (Coocconi), Mytilus galloprovincialis (Lamarck), Mytilaster lineatus (Gemelin in Linné) and Chlamys glabra. It was found that, in mollusk taxonomy, the elements have unique values. In other words, element concentrations in various mollusk shells depend mainly on the taxonomic characteristics of mollusks. In various bionomic environments different element distributions of the same species are attributed to the different geochemical characters of the each environment. Data obtained in this study indicate that the organisms are the most active and deterministic factors of the environment.