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Turbellaria (flatworms)


Dr. Maria Minor
Wildlife & Ecology Group
Massey University
Palmerston North
New Zealand

+64-06-356-9099 ext.84833

New Zealand Terrestrial & Freshwater Biodiversity Information System (TFBIS). Find out more...


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Undescribed native flatworm ("Australopacifica") from New Zealand.

Common name: terrestrial flatworms, land planarians, Maori toke.

Scienific name: phylum Platyhelminthes — “flat worms”, class Turbellaria, order Seriata, infraorder Terricola.


The flatworms (Turbellaria) are mostly marine, some inhabit fresh water, and the members of Terricola (terrestrial flatworms) live in moist terrestrial habitats. Terrestrial flatworms can be mistaken for slugs, but as the name suggests, the flatworms are more flattened dorso-ventrally.

Terrestrial flatworms are free-living soil animals, 0.5-10 cm in length, with flattened and unsegmented bodies. The size of a flatworm is not constant, as these animals can stretch out or contract considerably, changing shape as they move. Typically, the body is elongated, with narrower anterior and posterior ends. Eye spots may be present, but often are absent or very small, so that the head and tail ends of a flatworm are not easily identified if it is not moving. The movement is by a gliding motion, and a thin mucous trail is left behind the worm as it moves. The New Zealand flatworms are often colourful, with spots and stripes or in solid colours, in many shades of reddish-brown, purple, whitish, and black. Bodies of flatworms are usually very fragile, easily damaged by a slightest touch, and collected worms die and decompose quickly.

Notes on biology

Terrestrial flatworm (undescribed genus), North Island, New Zealand.

Terrestrial flatworms are predators that attack a range of small animals including slugs, snails, earthworms, and other soil invertebrates. Flatworms hunt actively in the soil, moving along crevices and burrows, as they follow the scented trail of their prey. The mouth of a flatworm is not on its anterior (head) end, but half-way down the length of the body, in the centre of the ventral surface. Multiple mouths can be present. The worm feeds by attaching itself to its prey with mucus, secreting digestive juices, and digesting the prey externally. Small prey animals can be swallowed whole. When food is not available, flatworms appear to be able to survive for over a year without feeding. Many terrestrial flatworms feed on earthworms, attacking and successfully feeding on earthworms up to 55 times larger than themselves (Zaborski, 2002).

One New Zealand flatworm Arthurdendyus triangulatus (Artioposthia triangulata), an earthworm-feeding species, has become a dreaded invasive species in Europe. This voracious carnivorous flatworm was accidentally introduced into parts of Northern Ireland, Scotland, and a few other places in the 1970s, and now causes serious problems in the soil by wiping out local earthworm populations. Arthurdendyus triangulatus has no preferred prey, but will eat any species of earthworm that it can find, at a rate of approximately one earthworm a week.

This flatworm has tied itself into a knot.

Egg cocoons of a terrestrial flatworm.

The skin of terrestrial flatworms is full of mucus glands, which secrete an abundant supply of mucus. The flatworms are slimy and very sticky, and leave behind mucus trail as they move. To protect itself from dessication, a flatworm can virtually tie itself into a knot, reducing the body surface exposed to the air. The thin layer of mucus envelops the knotted body, forming a protective cocoon. This mucus cocoon is easily broken once the worm decides to move.

The flatworm lays eggs protected by capsules or cocoons, the eggs hatch as miniature worms. Terrestrial flatworms are well known for their remarkable regeneration abilities, and some flatworms successfully reproduce by dividing into fragments. Each fragment then regenerates missing organs.

Where to find them?

Newzelandia sp., an endemic NZ flatworm.

Flatworms are very vulnerable to desiccation, so they are normally found in damp shady places — under logs and stones in native forests, in soil or under leaf litter. During the day, flatworms find refuge in damp places, but at night they can be seen in the open in habitats with high humidity, such as on the stones along forest stream beds or on the surface of moist soil. In and around human environments flatworms are often found under bricks, paving tiles, pieces of wood, or in folds of black garden plastic, in greenhouses, gardens, and plant nurseries. When looking for flatworms, place overturned logs and stones back into their original position — it will preserve the habitat for the flatworms and many other species.

Flatworms are active and colourful when observed live. Collecting and preserving flatworms is a difficult task and I don’t recommend it for a non-specialist. Their bodies are easily damaged when handled, and they are very sensitive to heat and dessication; captured flatworms may die quickly and decompose within hours. When fixed in alcohol, flatworms lose their shape and colours, so identification is based on the internal anatomy.

Distribution and conservation

Flatworms are found throughout New Zealand, but their diversity, fauna, and distribution are still poorly known. More than 100 different species of terrestrial flatworms are expected to exist in New Zealand, but most species are undescribed, and little is known about their distribution, ecology, or impact on other invertebrates. Artioposthia mariae, a flatworm recorded from Golden Bay and Motueka in the South Island has been listed as a protected species by the NZ Department of Conservation, but the threats and conservation status for this species are unknown.

Worldwide, distributions of terrestrial flatworms have been extended significantly by humans, as flatworms are easily spread via the trade of potted plants. The “New Zealand flatworm” Arthurdendyus triangulatus and other Australasian species are now found in the British Isles and Faroe Islands. In return, exotic species have become established in New Zealand. Terrestrial flatworms are fascinating organisms; because of their potential for human-mediated spread, more data on their natural distribution and biology is required.

Included images:

Order Seriata
Family Geoplanidae
Arthurdendyus (=Artioposthia) testaceus (Hutton, 1880) - Palmerston North, WI, North Island (2 images)
Arthurdendyus (=Artioposthia) sp. undescribed - Canaan Road near Harwood Hole, NN, South Island (2 images)
Arthurdendyus (=Artioposthia)? sp. - Peel Forest, Dennistoun Bush, SC, South Island (3 images)
Arthurdendyus triangulatus (Dendy, 1894) - Temple Valley, Lake Ohau, MK, South Island
Arthurdendyus triangulatus (Dendy, 1894) - Temple Valley, Lake Ohau, MK, South Island
'Australoplana' sp. undescribed - Nelson, NN, South Island
Australopacifica maori - Craigieburn Forest Park, Broken River Road, Jacks Pass, NC, South Island (2 images)
Australopacifica nr. suteri (Dendy, 1897) - Kaiteriteri Road, NN, South Island
'Australopacifica' sp. - Craigieburn Forest Park, Lyndon Hutt, NC, South Island (2 images)
Australopacifica sp. undescribed - Ohinetonga Scenic Reserve, TO, North Island (3 images)
Kontikia sp. - Palmerston North, WI, North Island
Newzealandia sp. undescribed - Palmerston North, WI, North Island (2 images)
Newzealandia sp. undescribed - Palmerston North, WI, North Island (2 images)
'Australopacifica' sp. - Torlesse Range, Porters Pass, NC, South Island (2 images)
Newzealandia sp. undescribed - Rimu Valley Walk, SD, South Island
Artioposthia exulans (Dendy, 1901) - Kawhatau Base, RI, North Island
Newzealandia nr. moseleyi (Hutton, 1880) - Peel Forest, Dennistoun Bush, SC, South Island (2 images)
'Australopacifica'- Hawdon Valley, NC, South Island
'Australopacifica' species - Ohinetonga, TO, North Island
'Australopacifica' species - Peel Forest Park, Dennistoun Bush, SC, South Island (2 images)
'Australopacifica' species - Peel Forest Park, Dennistoun Bush, SC, South Island (3 images)
'Australopacifica' species - Katikara Stream, Taranaki, TK, North Island
'Australopacifica' species - Katikara Stream, Taranaki, TK, North Island (3 images)
'Australopacifica' species - Katikara Stream, Taranaki, TK, North Island (2 images)
Flatworm egg capsules - Palmerston North, WI, North Island

Further information on New Zealand terrestrial flatworms:

Cannon L.R.G. 1986. Turbellaria of the World - a Guide to Families and Genera. Queensland Museum, Southern Brisbane, Australia. 136 p.

Johns P.M., Boag B. 2003. The spread and distribution of terrestrial planarians (Turbellaria: Tricladida: Geoplanidae) within New Zealand. New Zealand Journal of Ecology 27, p. 201-206.

Johns P.M., Boag B., Yeates G.W. 1998. Observations on the geographic distribution of flatworms (Turbellaria : Rhynchodemidae, Bipaliidae, Geoplanidae) in New Zealand. Pedobiologia 42, p. 469-476.

Yeates G.W. (Ed.) 1998. OECD Workshop on Terrestrial Flatworms. New Zealand, 1998. Pedobiologia 42, 199 p.

Sluys R. 1999. Global diversity of land planarians (Platyhelminthes, Tricladida, Terricola): a new indicator-taxon in biodiversity and conservation studies. Biodiversity and Conservation 8, p. 1663-1681.

Winsor L, Stevens M.I. 2005. Terrestrial flatworms (Platyhelminthes:
Tricladida: Terricola) from sub-Antarctic Macquarie Island. Kanunnah 1, p. 17-32.

Turbellaria Resources on the Web

Terrestrial Flatworms, by Andrew Fraser, some information on terrstrial flatworms in Britain.

Flatworms, Landcare Research, New Zealand, brief description.

Fauna Europaea: Terricola, taxonomy of Terricola and checklist of European species.

Checklist of the Italian fauna on-line, checklist of Italian Turbellaria.

Browse our

NZ Flatworms

Links and Resources:

Terrestrial Flatworms, flatworms of Britain

Flatworms, NZ

Fauna Europaea: Terricola

Checklist of the Italian fauna on-line


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