Placostylus hongii at the Mokohinau Islands

An extant population of the large, north-eastern New Zealand endemic landsnail Placostylus hongii is recorded here from a small islet (0.25 ha) 50 m offshore from Fanal Island in the Mokohinau group. The only previous records ofP. hongii from the Mokohinaus were of old empty shells from Fanal Island, where the species evidently became extinct at some time prior to the 1930s. The extant Mokohinau population is relatively small and is dominated by adults. In November 1996 it comprised at least 120 but probably not more than 200 individuals. Shells are among the smallest known for the species, with adult shell heights ranging from 53.8 to 71.3 mm. Further, the population is unique in that apertures of adult shells are exclusively cream-coloured rather than the red-orange colour which is more typical of the species. There are no known direct threats to the survival of the Mokohinau population at present, but the potential for catastrophic changes in habitat structure, or invasion of kiore (Rattus exulans) from Fanal Island, are of concern, given the existing small size and restricted distribution area of the snail population.