Question

What are the features of each the classes;.... Monoplacophora, Polyplacophora, Pelecypoda, Gastropoda, Scaphopoda, Aplacophora

Answer 1

The phylum Mollusca consists of 8 classes; Chaetodermomorpha, Neomeniomorpha, Monoplacophora, Polyplacophora, Scaphopoda, Cephalopoda, Gastropoda and Bivalvia however the latter two classes contain 98% of the known molluscan species (Barnes et al., 1988). The uptake and subsequent bioaccumulation of anthropogenic xenobiotics from the aquatic environment has been examined in numerous freshwater and marine molluscan species (Doyotte et al., 1997; Livingstone 1991, 1992, 1994; O'Connor 1996).

Contaminants including polycyclic aromatic hydrocarbons (PAHs) (Baumard et al., 1998; Krishnakumar et al., 1997; Næs et al., 1998), polychlorobiphenyls (PCBs) (Krishnakumar et al., 1997; Livingstone et al., 1997; O'Connor, 1996), organophosphates (Dauberschmidt et al., 1997; McHenery et al., 1997), organometals (Morcillo et al., 1997; Page et al., 1995), thiocarbamates (Doyotte et al., 1997) and metals (Doyotte et al., 1997; Viarengo et al., 1997; Walsh & O'Halloran, 1998) are biologically available to molluscs and uptake is proposed to occur from the sediment, suspended particulate matter, water-column and food sources (Livingstone 1991, 1992; Krishnakumar et al., 1997)

The major routes of uptake of these contaminants will depend upon the dietary and ecological lifestyle of the particular organism however the processes of uptake of the organic contaminants are largely passive determined by physico-chemical principles viz. molluscan tissue body burden increases with increased external concentration, bioavailability and lipophilicity of the xenobiotic (Livingstone & Goldfarb, 1998). Due to the apparent low rates of biotransformation of the contaminants to polar metabolites, the resultant slow elimination of xenobiotics from molluscan tissue leads to the bioaccumulation of contaminants (Livingstone 1994) and thus filter feeder bivalves such as Mytilus sp. have been extensively employed worldwide as a measure of marine environmental pollution (Livingstone & Goldfarb, 1998

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