Pseudo-polymorphism in Nerita polita is mainly due to changes in colour and pattern with age. Only a fraction of these changes is visible in a single individual. The result is that a population includes a mixture of characteristic types which intergrade with each other. As in Clithon and Umbonium, a few discrete variants are probably the result of conventional polymorphism.
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Hans Grüneberg (1981) studied this question.
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