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DescriptionSmooth, translucent brownish yellow - horn coloured shell, up to 2 cm in length and much smaller than the common limpet (Patella spp.). Oval in outline in the shape of a depressed cone with the apex at the anterior end. The shell is overlayed by 2-8, characteristic, broken (dashed) blue-green rays, although these are absent from the juvenile shell until they reach 1.1mm in length.Specimens found in cavities in holdfasts develop into the laevis form (Helcion pellucidum var. laevis). The laevis form has a taller, more robust opaque shell, ledged in profile, with blue rays that alternate with reddish brown rays. The most noticeable ledge of the shell indicates the size at which the individual enters the holdfast.
Weber et al. (1997) suggested that Helcion pellucidum was genetically distinct from its South African con-geners and may have arisen independently. Recent studies of morphological features (Ridgeway et al., 1998) and molecular characteristics (Koufopanou et al., 1999) suggest that Helcion pelludicum belongs to the genus Patella.