Overview
Snails and slugs, known as gastropods, or univalves, are the largest and most successful group of molluscs, and occupy all habitats from alpine regions to the depths of oceanic trenches.
Most gastropods have a single shell which is coiled, and usually opens on the right hand side (as viewed with the shell apex pointing upward). Some species are cap shaped (limpets). Many species have an operculum of a horny or calcareous material that operates as a plug to close the opening to the shell.
More than two thirds of all gastropod species are marine and include herbivores, detritus feeders, carnivores and a few ciliary feeders. Limpets and pāua are common around New Zealand: both groups are herbivores and use their hard radula to rasp at algae on rocks. Other marine gastropods are burrowers and have siphons that extend from the mantle that act as snorkels, for respiration and excretion, and detect chemicals in the water that may indicate predators or prey.
In slugs, the shell is reduced or absent, and the body is streamlined. Sea slugs or nudibranchs are often brightly coloured and poisonous. Many species have feathery plume-like gills on their backs which gives rise to the name, nudibranchs. Sea slugs are herbivores or carnivores.