| Mollusca
Suteria ide, a native New Zealand snail which lives in forest litter. The shell of this snail is only ~ 9 mm in size.
Common name: snails, slugs, Maori ngata.
Scientific name: phylum Mollusca, class Gastropoda, from Greek "gaster", stomach, and "podus", foot - referring to their crawling way of locomotion.
Description
Slugs and snails belong to the class Gastropoda of molluscs (soft-bodied animals). Most gastropods are aquatic, but one group (subclass Pulmonata) have expanded into terrestrial habitats. Terrestrial snails and slugs in New Zealand are extremely diverse, and come in a variety of colours, shapes and sizes. Most of the native snails found in forest letter are only a few millimetres in size, while the shell of the giant native snail Powelliphanta can reach 5-6 cm in diameter.
The general body plan in all gastropods is similar. They have a flat, muscular foot, on which they move around. On the front end of the body is the head, which bears 1-2 pairs of tentacles, a mouth, and the organs of sense. These are well developed, and include organs of touch, smell and sight. The eyes are usually located on the tips of the tentacles (if 2 pairs of tentacles, at the tips of the larger pair). The mouth contains a rasping tongue-like device called the radula, which slugs and snails use in feeding. The rest of the internal organs are contained within the soft hump of the body - the visceral mass. In terrestrial snails, the visceral mass is coiled into a spiral and hidden within the coiled shell, so that only the head and the foot extend outwardly.
The snail shell is constructed from calcareous material covered outside with a thin layer of horn-like protein, which gives the shell its colour. The shell is secreted along its opening and as the snail grows larger, each successive whorl is made larger than the previous one. A special muscle allows the snail to retract its head and foot into the shell to protect the snail from predators. Different species of New Zealand land snails have variously shaped and sized shells, often ornamented with ridges, ribs, and bristle-like processes. Snails require calcium for shell production, so are often more diverse and numerous in calcium-rich soils. Land snails and slugs loose moisture freely through the skin, and require a humid environment. Because of the drying effect of the sun, most slugs and snails are nocturnal. Snail shells offer some protection from dessication when the body is fully retracted. Slugs are the gastropods that have partly or completely lost the shell. The division between snails and slugs is rather arbitrary - some slugs, for example the native "paua slugs" Schizoglossa, have small external vestigial shell, while in the endemic New Zealand slug-like snail Otoconcha the shell is fully internal. In most slugs the shell is internal or absent completely, and their bodies are cylindrical or flattened. Features of the shell, the external morphology, and the internal anatomy (for slugs) are important in the identification of species.
Giant snails and Kauri snails (also known by its Maori name pupu rangi)
Paryphanta watti Powell, 1946. Photo courtesy of Ian Stringer, NZ Dept. of Conservation.
These are the largest of the New Zealand land snails. The shell of the Superb snail - Powelliphanta superba - can exceed 10 cm in diameter. There are many species of giant snails (Powelliphanta spp.), found in the damp leaf litter in many locations from the central North Island to the north-western, western and southern South Island. The shiny coiled shells of Kauri snails (Paryphanta spp.) are 6-7.5 cm across. These snails live in the leaf litter of moist forests and native scrubs of the northern North Island of New Zealand. Both the kauri snails and the giant snails are carnivorous, feeding mostly on earthworms, but also on other soft-bodied soil invertebrates. These snails are nocturnal, spending the day buried in the leaf litter and coming out on warm, moist nights to feed and reproduce. Prone to dehydration, giant and kauri snails are inactive in dry conditions, and prefer rainforests and damp mountain forests as habitats.
A colony of flax snails - Placostylus ambagiosus (Powell, 1979). Photo courtesy of Ian Stringer, NZ Dept. of Conservation.
Flax snails (pupu harakeke)
Flax snails (Placostylus spp.) are found in the coastal broadleaf forests and scrubs of the northern North Island. The tall, spired shell of these large snails can reach more than 8 cm in length. Flax snails are nocturnal: during the day the adults hide in the leaf litter, feeding at night on fallen leaves. Young flax snails live on the leaves in tree canopes, only coming to live on the ground when they are suficiently large.
The different (and large) species of Placostylus snail lives in the forests of New Caledonia, where it is considered to be a delicacy by the locals.
Leaf-veined slugs (putoko)
Pseudaneitea gigantea, a native New Zealand slug.
There are many species of native New Zealand slugs, and all of them can be recognized by the characteristic leaf-vein pattern on their dorsal side. This leaf-vein pattern is absent in introduced species. New Zealand native slugs belong to the family Athoracophoridae, there are about 30 species, most of which are NZ endemics. Related slugs are found in New Guinea, eastern Australia, New Caledonia, and Vanuatu. Their biology is poorly studied, they are thought to feed on algae and fungi that grow on the surface of plants. These slugs do not damage garden plants.
Notes on biology
All terrestrial slugs and snails are hermaphrodites (having both male and female reproductive organs), but they need to mate to fertilize each other's eggs. After mating, slugs and snails lay clutches of eggs in a nest - in soil under the leaf litter (Powelliphanta and flax snails), under the bark of rotting logs (some native slugs), or in similar protected places. Some species, such as native slugs, have soft, jelly-like eggs, while flax snails and kauri snails have eggs with a hard, calcified shell. The eggs can be quite large - up to about 13 mm in diameter in giant snails. The eggs develop for some time; the young snail and slug hatchlings resemble adults.
Eggs of a native New Zealand slug.
Life cycles of many New Zealand native land molluscs are unknown, although more information exists on large protected species. We know that kauri and Powelliphanta snails reproduce very slowly; each snail will produce only ~ 5 eggs in a year. Young snails live in the forest litter, feeding on rotting leaves. They grow very slowly, taking more than 10 years to reach the adult stage. The adult kauri and Powelliphanta snails live for a long time: 20+ years is often given as their lifespan.
The majority of native New Zealand snails are fungivores and detritivores, feeding on fungi associated with decay, on dead leaves in the litter layer (e.g., flax snails), and on microscopic algae which grow on the surfaces of leaves and bark. Introduced snails and slugs are primarily herbivores, feeding on green plant tissues. Few groups, such as giant snails (Powelliphanta spp.), kauri snails (Paryphanta spp.), species of Rythida and Wainuia (family Rhytididae), etc., are carnivorous, eating earthworms, other snails, slugs, and even agile landhoppers (Efford, 2000). In return, snails and slugs are preyed upon by invertebrate and vertebrate predators - ground beetles, terrestrial flatworms (Barker, 1989), native birds. Many introduced species - rats, pigs, hedgehogs, stoats, possums, thrushes and blackbirds - prey on land gastropods.
Where to find them?
Terrestrial slugs and snails are common inhabitants of New Zealand forests, grasslands, and shrublands. They can be found in the forest leaf litter, under the loose bark of rotting logs, under moss, in humus at the bases of trees, and in many similar damp, protected habitats. Introduced species are more common in and around human settlements, in farmlands, parks and gardens, where they hide under stones, tiles, old boards, and piles of debris. At night, when slugs and snails are active, many can be observed in the open - on the surfaces of tree trunks and dead logs, on the leaves and branches of plants, even on urban sidewalks and the walls of houses. Small land snails can be collected and preserved dry, but their identification is difficult. Slugs can be preserved and stored in 75% alcohol, but they contract their bodies and loose all shape and colour, so collecting them is unfulfilling. Giant snails, kauri snails, and flax snails are protected by New Zealand law and no collection of live snails or dead shells is permitted.
Distribution and conservation
Powelliphanta hochstetteri (Pfeiffer, 1862)
Nearly 35 000 species of terrestrial slugs and snails are described worldwide. They can be found from near-polar regions to the equator. The New Zealand fauna of terrestrial slugs and snails is particularly rich - in fact, New Zealand forests host the richest land snail communities found anywhere in the world (most of these snails are minute). Nearly all of New Zealand's 1400+ species of land slugs and snails are endemic, while many families have Gondwanan connections. New Zealand terrestrial gastropods, particularly the minute land snails, remain poorly studied. Little information is available on their diversity, ecology, distribution, or conservation value. Hundreds of species are still undescribed.
The focal point of New Zealand research and conservation in land molluscs are the species and subspecies of giant snails (Powelliphanta spp.), kauri snails (Paryphanta spp.), and flax snails (Placostylus spp.). These snails are a unique feature of the New Zealand land fauna; once widespread, they are now endangered or threatened throughout their range. The species of Powelliphanta, Paryphanta, and Placostylus have the status of Nationally Threatened Invertebrates, and are protected and intensively studied by the New Zealand Department of Conservation. The causes of decline for all large land snails are similar - it is the destruction of their habitat by introduced herbivores - goats and deer, and by humans, who have cleared the forests for agriculture. Even more serious threat are the introduced mammals - pigs, rats, and possums - that prey on adult snails. Introduced birds eat snail eggs and smaller snails. As a result, many of these unique snails now survive only in small reserves where they are protected and where the predators are controlled.
"Tiger slug" Limax maximus (L.) is the largest slug introduced to New Zealand from Europe. Tiger slugs eat plant matter, but also prey on other slugs.
Similar to most other invertebrates, terrestrial slugs and snails are easily spread with plants, soil, fruits, garden materials, etc., along human trade routes. Many European and North American species have established successfully outside of their original range. Currently, there are 30 species of introduced slugs and snails in the New Zealand fauna, most of them associated with human-modified habitats and crops. The commonly encountered exotic species are the grey field slug Deroceras reticulatum, the yellow cellar slug Lumacus flavus, and the garden snail, Cantareus aspersus (formerly Helix aspersa). Introduced herbivorous slugs and snails can be a severe problem in pastures, gardens, and croplands, damaging and killing plants and their seedlings.
Included images:
- Order Pulmonata
- Family Athoracophoridae
- Pseudaneitea gigantea (Suter, 1909) - Canaan Road near Harwood Hole, NN, South Island (2 images)
- Pseudaneitea pseudophyllum (Burton, 1963) - Peel Forest, Dennistoun Bush, SC, South Island (3 images)
- Pseudaneitea sp. - Craigieburn Forest Park, Broken River Road, Jacks Pass, NC, South Island
- Pseudaneitea sp. - Craigieburn Forest Park, Lyndon Hutt, NC, South Island
- Pseudaneitea sp. - Hawdon Valley, NC, North Island
- Athoracophorus bitentaculatus (Quoy & Gaimard, 1832) - Ohinetonga Scenic Reserve, TO, North Island (2 images)
- Athoracophorus bitentaculatus (Quoy & Gaimard, 1832) - Ohinetonga Scenic Reserve, TO, North Island
- Athoracophorus sp. undescribed - Omahuta Forest, Northland, ND, North Island
- Athoracophorus sp. juvenile - Makahika, WN, North Island (2 images)
- Family Limacidae
- Limacus flavus (L., 1758)* - Palmerston North, WI, North Island (2 images)
- Limax maximus (L., 1758)* - Te Purere, TO, North Island (2 images)
- Family Arionidae
- Arion hortensis (Férussac, 1819)* - Ohinetonga, TO, North Island (2 images)
- Family Paryphantidae
- Rhytida sp. - Ohinetonga Scenic Reserve, TO, North Island
- Powelliphanta hochstetteri (Pfeiffer, 1862) - Canaan Road, NN, South Island (2 images)
- Paryphanta busbyi busbyi (Gray, 1840) - Trounson Kauri Park, Northland, ND, North Island
- Family Endodontidae
- Flammulina zebra (Le Guillou, 1842) - Kaiteriteri Road, NN, South Island (2 images)
- Suteria ide (Gray, 1850) - Ohinetonga Scenic Reserve, TO, North Island (3 images)
- Family Charopidae
- Charopa montivaga (Suter, 1894) - Craigieburn Forest Park, Cave Stream, NC, South Island (5 images)
- Aeschrodomus stipulata (Reeve, 1852) - Peel Forest, Dennistoun Bush, SC, South Island
- Otoconcha dimidiata (Pfeiffer, 1853) - Katikara Stream, Taranaki, TK, North Island (2 images)
- Family Zontidae
- Oxychilus alliarius (Miller, 1822)* - Kahurangi Nation Park, NN, South Island (2 images)
- Oxychilus cellarius (Müller, 1774)* - Nelson, NN, South Island (2 images)
- Family Helicidae
- Cantareus aspersus (Müller, 1774)* - Palmerston North, WI, North Island
- Other
- Unidentified species - Ohinetonga Scenic Reserve, TO, North Island
- Unidentified species - Canaan Road near Harwood Hole, NN, South Island (2 images)
- Unidentified species - Hawdon Valley, NC, South Island
- Unidentified species - Hinewai Reserve, Banks Penninsula, MC, South Island (3 images)
- Unidentified species - Peel Forest, Dennistoun Bush, SC, South Island (2 images)
- Unidentified species - Katikara Stream, Taranaki, TK, North Island (2 images)
- Unidentified species - Trounson Kauri Park, Northland, ND, North Island
- Unidentified species - Takapari Road, Southern Ruahine Ranges, RI/WI, North Island
- Unidentified species - Palmerston North, WI, North Island
- * - species exotic in NZ
Further information on New Zealand terrestrial Gastropoda:
Barker, G.M. 1989. Flatworm predation of terrestrial molluscs in New Zealand, and a brief review of previous records. New Zealand Entomologist, Vol. 12.
Barker, G.M. 1992. Naturalised terrestrial molluscs in New Zealand: Origins and establishment Proceedings of the Annual Conference of the Entomological Society of New Zealand 41, p. 54-62.
Barker, G.M. 1999. Naturalised terrestrial Stylommatophora (Mollusca: Gastropoda). Fauna of New Zealand 38, Lincoln: Manaaki Whenua Press. 253 pages.
Barker, G.M. 2001.Gastropods on land: phylogeny, diversity and adaptive morphology, pp1-146. In: Biology of Terrestrial Molluscs (Barker, G M, ed.). Wallingford, CABI Publishing.
Barker, G.M., Mayhill, P.C. 1998. Patterns of diversity and habitat relationships in terrestrial mollusc communities of the Pukeamaru Ecological District, northeastern New Zealand. Journal of Biogeography 25, p. 215-238.
Barker, G.M, Watts, C. 2002. Management of the invasive alien snail Cantareus aspersus in the conservation estate. DOC Science Internal Series. Wellington, Department of Conservation. 30 p.
Burton, D.W. 1963. A revision of the New Zealand and Subantarctic Athoracophoridae, Transactions of the Royal Society of NZ, Zoology 3(6), p. 47-75.
Efford, M. 2000. Consumption of amphipods by the New Zealand land snail Wainuia urnula (Pulmonata: Rhytididae). Journal of Molluscan Studies 66, p. 45-52.
Jones, J. 2001. Land Snails. Heinemann Education, Auckland. 24 p.
Solem, A., Climo, F.M, Roscoe, D.J. 1981.Sympatric species diversity of New Zealand land snails. New Zealand Journal of Zoology 8, p. 453-485.
Land Gastropoda Resources on the Web Powelliphanta Land Snails - NZ Department of Conservation, detailed information on Powelliphanta ecology, threats to survival, and conservation.
Bug identification - Slugs, snails & worms - Identification Guide to Common Invertebrates of New Zealand, Landcare Research. Research on Terrestrial Molluscs, Te Papa Tongarewa - The Museum of New Zealand. The overview of the unique fauna of New Zealand terrestrial molluscs.
Research on Alien Molluscs - by Gary Barker, Te Papa Tongarewa - The Museum of New Zealand. Check-list of species introduced and naturalized in NZ.
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