Simultaneous polyphenism and cryptic species in an intertidal limpet from New Zealand.

The small intertidal limpets known under the name Notoacmea helmsi occupy a wide variety of habitats in New Zealand and exhibit a variety of shell forms. Phylogenetic analyses of DNA sequences from two genes, mitochondrial COI and nuclear ITS1, reveal that this taxon comprises at least five morphologically cryptic species, with at least one of these species, N. scapha, consisting of individuals with two obviously different shell types. One of these forms is an ecophenotypic response to living on eelgrass (Zostera) fronds. Unlike its extinct relative, Lottia alveus, N. scapha is not restricted to this substrate, but individuals living elsewhere are larger and have a different shell shape. Although there is significant overlap in shell form among the different cryptic species, there is some habitat differentiation, with two species predominantly found on exposed shores and three confined to mudflats. One species exhibits distinctive light-avoiding behaviour, the first known case in which behaviour can be used to separate cryptic species in molluscs.