Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Mollusca
Class Gastropoda
Informal group Pulmonata
Clade Systellommatophora
Common names: land slugs, slug-like pulminates
Overview
Terrestrial Systellommatophora are slug-like in appearance, but differ from true slugs (Stylommatophora) by the absence of the mantle cavity. They are medium sized, soft, brown, dorso-ventrally flattened slugs that usually have a uniform body with no regionalisation evident from external examination of a live animal. The head is typically hidden under a short anterior extension of the dorsal mantle. Two pairs of retractile head tentacles are present with the dorsal pair with eyes at the tips and typically larger than the ventral pair (which may be very small). All apertures (mouth, pneumostome, excretory and reproductive pores) open ventrally (to the front of the body). The family Veronicellidae do not have the pulmonate lung and instead respirate through their skin. The species of Rathouisiidae found in Australia are characterised by a sharply rounded or keeled notum, giving the animal an almost triangular cross section.
Distribution and diversity
There are three families in the Systellommatophora: the marine Onchidiidae and the terrestrial Rathouisiidae and Veronicellidae. Representatives of the Rathouisiidae occur in southern China, Burma and Thailand, through Indonesia, the Philippines, and New Guinea to northern and eastern Australia. Two Australian species are found the wet forests of tropical and subtropical eastern Australia. Veronicellidae have a worldwide tropical distribution except for North Africa and the Middle East, where no veronicellids are found. There are also some species in cool temperate habitats in both the southern and northern hemispheres. The two species that occur across tropical and subtropical Australia are introduced cosmopolitan tramp species.
Life cycle
Systellommatophora are hermaphroditic. Individuals are capable of fertilising or being fertilised, but only a few species are able to do so simultaneously, since in all but a few exceptions, sperm and unfertilised eggs mature at different times. Most species can self-fertilise. Veronicellidae are protandrous hermaphrodites, being initially male then becoming female later in life. Clutches of gelatinous eggs are laid on the ground in moist, concealed locations. Young slugs are often lighter in color than adults and are active and feed as soon as they hatch if temperature and humidity are suitable.
Feeding
Rathouisiidae are carnivorous slugs that prey on other slugs and snails using slender dagger-shaped teeth. At times they will also consume fungi and vegetable matter. Veronicellidae are herbivorous, feeding on fungi and dead and living plant material, including garden and crop plants.
Ecology
Systellommatophora occur in humid environments and are active at dusk, dawn and during the night. Diurnally they take refuge under stones, leaf litter or other material on the ground, however light rainfall can induce foraging during the day. Australian species of Rathouisiidae are found in the deep litter of the wet tropical and subtropical forests and, at times, can also be arboreal. Veronicellidae live under stones, grass tussocks or decaying wood. Several veronicellid species are tramps and have been widely distributed by commerce over the last two centuries, including the two species recorded in Australia where they are considered pests in some Queensland and Northern Territory gardens, particularly in Brisbane and Darwin. Elsewhere some veronicellids are known to be vectors of parasitic nematodes of vertebrates.
