Morphological identification of primary settlers and post-larvae of three mussel species from the coast of South Africa

The study of mussel settlement and recruitment requires the ability to identify the larvae of co-existing species. On the south coast of South Africa, an introduced (Mytilus galloprovincialis) and two indigenous (Choromytilus meridionalis and Perna perna) mussel species co-exist and compete for space. One of the indigenous species (P. perna) is invasive elsewhere. We provide discriminating features of their settlers based on post-larval shell morphology and hinge structure. Early post-larvae of P. perna can be identified by shell markings and shape. Small post-larvae of M. galloprovincialis and C. meridionalis are difficult to separate, but this can be done based on the proportions of the shell; larger post-larvae of M. galloprovincialis have diagnostic hair-like structures on the dissoconch. Detailed descriptions are provided that allow unambiguous identification of each species at sizes from 330 mu m to 5 mm.