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The cuttlefish, Sepia officinalis L., liver was investigated by histochemical and microanalytical methods. The greater part of the accumulated Cu is concentrated in spherulae which are elaborated by the basal cells. Cu is associated with both Ag and Zn. Fe is also found but the digestive cells are the most important site of Fe storage. Our data show that the spherulae are made of metallothionein-like proteins. The occurrence of these metal-binding proteins has ecological effects. The metals are easily assimilable and can be transferred to higher levels of the food chain.

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High loads of heavy metals can be found in some marine species either due to their peculiar physiology or due to the level of pollution of the medium they are living in. The first case is illustrated by copper loads of species using haemocyanin as oxygencarrier and iron loads of species using haemoglobin. The other case is, for example, that of mollusc species living in the Severn Estuary, highly polluted by heavy metals: they contain more Cd, Cu and Zn than molluscs of the same species living in unpolluted mediums (Noel-Lambot et al . .1978). Metabolic and toxic effects of metal ions have been reviewed in mollusca by Simkiss and Mason (1983). Excesses of essential metals as well as the presence in large amounts of non-essential ones, due to inappropriate intracellular binding, may be toxic for those species when the excess of metal is not stored in the animal under a detoxified form. Heavy metals can be stored an detoxified by marine organisms either by a compartmentation process within membrane-litnited vesicles or by binding to specific proteins.