Within the genus Perna usually four species are distinguished, viz., the green mussel Perna viridis (Linnaeus, 1758), the brown mussel Perna perna (Linnaeus, 1758), the green-lipped mussel Perna canaliculus (Gmelin, 1791) and the Spanish mussel (Mediterranean green mussel) Perna picta
(Born, 1780) (Figure 1). P. canaliculus and P. picta are geographically restricted to New Zealand and the Mediterranean Sea, respectively. However, the other two species enjoy wide distribution
in several parts of the world (Siddall 1980; Vakily 1989; Hicks et al. 2001)