Unio pictorum, also known as the "painters' mussel", could easily be mistaken for a large mussel. Yellow-brown in color, its shell features regularly spaced dark bands, marking different periods of growth. Adults live for more than 20 years. 15 cm long, 3 to 4 cm high and 3 cm wide, its shell was historically used as a conveniently sized and shaped receptacle for holding artist's paint. Today, the painter’s mussel plays a role in water purification by continuously filtering planktonic algae, bacteria and micro-particles. Used as a bio-indicator, scientists measure trace metal levels in its tissues to assess the presence of metals in the environment.