A burrowing species which spends much of its life buried several centimetres into the bottom substrate (4) (7) (8), the clubshell pearly mussel is a relatively little-known species (7).
Mussels are filter feeders, taking in water via one opening in the shell, known as the ‘inhalant aperture’, and expelling waste via another opening, known as the ‘exhalant aperture’. These apertures, along with the foot, aid in breathing, feeding and reproduction. They are the only parts of the body that emerge from the shell, but can be withdrawn very quickly to prevent predation (9). To breathe and feed, the clubshell pearly mussel relies on the water percolating between the particles of the sandy substrate in which it lives (8). Mussels respire via gills that absorb oxygen from the water, and although they are fairly inefficient at absorbing oxygen, they make up for this by having large gills and, where possible, a high volume of water passing over them (9).
Breeding in the clubshell pearly mussel involves males discharging sperm into the river current, which then travels downstream where the females siphon in the sperm to fertilise their eggs (7). Following fertilisation, the eggs are stored in the female’s gill pouches where they develop and hatch out as larvae (4) (7), known as ‘glochidia’ (4). The clubshell pearly mussel then releases the glochidia into the water (4) (7). Interestingly, like most other freshwater mussels in the Unionidae family, the clubshell pearly mussel requires a fish host in order to complete its life cycle (4). The glochidia of the clubshell pearly mussel must use tiny clasping valves to attach themselves to the gills of a host fish species (7) such as the blackside darter (Percina maculata), central stoneroller (Campostoma anomalum), logperch (Percina caprodes) and striped shiner (Luxilus chrysocephalus) (4).
Mussel glochidia remain attached to the fish host for up to several months, depending on the species in question (4), and grow into juveniles with shells of their own. Once the adult form has been attained, the mussel detaches itself from its fish host (4) (7) and settles into the streambed (7). It is thought that one benefit of having a fish host is dispersal, helping to ensure that mussels are transported to new habitats and that gene flow between populations is facilitated (4).
The maximum lifespan of the clubshell pearly mussel is an impressive 50 years (4) (7).