At first sight, unionid freshwater mussels neither sound nor look very interesting. However, studying them for my PhD, I quickly became fascinated with this group of animals. Actually, when you have a proper look at these large-shelled bivalves, they are quite beautiful. In Europe we only have a handful of species, but in North America their variety is immense.
Some species can live very long, up to 250 years, and they can even produce pearls. Unfortunately many species are also critically endangered because of habitat loss and introduction of invading species that overgrow our out-compete native species.
My favourite freshwater mussel fact is that they have larvae (glochidia) that are parasitic on the gills of fish. Many species have specific host species, and some have evolved very elaborate methods to target their hosts. For example, in some species the glochidia form a “lure” that closely resembles the prey of the host fish, gets eaten, and the glochidiae end up on the gills.
The most amazing behaviour is displayed by the “Snuffbox”. It actually catches the host fish between the valves of the shell and “pumps” the glochidia into its gills. A video can be found here. Highly recommended!