1: white proboscis everted into paralysed body of Mytilus edulis.
2: foot holding apart valves of M. edulis.
3: valve of M. edulis.
Mytilus edulis is often most frequent prey of N. lapillus in extreme S.W. England, where the usually favoured prey, Semibalanus balanoides (barnacle), is rare or absent (settlement and survival vary greatly with weather from year to year, Lewis, 1964, pp.250-251). M. edulis may also be utilized in other areas on very sheltered shores where the sweep of fucoids restricts barnacle settlement.