Host fishes (Boops boops) parasitized by the cymothoid isopod Meinertia oestroides show an atrophied tonuge: its length and its initial weight can decrease of about 50%. These morphological variations are connected with deep histological alterations, such as: A more or less important vanishing of epidermis. A disorganization of the connective tissue, by numerous invading blood cells. A total vanishing of cargilage and a partial vanishing of bone, resulting from the lysis of their own fundamental substance.