Lysosomes in digestive gland of mussels maintained in 18 ◦Cseawater for 24 h appeared as sparse and small cytoplasmic vesicles reactive for GUSB. Instead, after maintenance in 26 ◦C seawater reactive lysosomes were more conspicuous (Fig. 2B and F). Likewise, lysosomes were more evident at 26 ◦C than at 18 ◦C in Cd exposed mussels (Fig. 2D and H). Lysosomal enlargement was accompanied by evident thinning of the digestive epithelium (Fig. 2C and G).