The purple wartyback (Cyclonaias tuberculata) is a rather distinctive mollusc, named partly for the many bumps or ‘warts’ covering much of its outer shell (4) (5). The fairly thick, heavy and roughly circular shell is usually brown or black on the outside, although it varies from yellow-brown to green-brown in young individuals and becomes darker with age (3) (4).
The outer shell of the purple wartyback often closely resembles the shells of other freshwater mussels, such as the pimpleback (Quadrula pustulosa) and the mapleleaf (Quadrula quadrula). However, the purple wartyback may be differentiated from these similar species by its iridescent purple ‘nacre’ (a material produced by the mollusc as an inner shell layer), which varies in colour from off-whitish to coppery-indigo or deep purple (4) (5).
There is a visible bulge or ridge on the outer shell surface, known as the beak, which is covered in wavy lines (5), while a square, flattened extension is found where the two halves of the purple wartyback’s shell join (2). The inside of the shell has large, distinctive, triangular-shaped ‘teeth’ as well as heavy, elongated teeth along the hinge line of the shell (3) (4).
- Length: up to 12.7 cm (2) (3)