T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Flatworm (Family: Geoplanidae) Land planarians

Kingdom: Animalia
Phylum: Platyhelminthes
Class: Turbellaria
Order: Tricladida
Suborder: Continenticola
Family: Geoplanidae
Common name: Land planarians
Geoplanidae is a family of flatworms known commonly as land planarians. They have a world wide distribution. 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.
Land planarians are voracious predators of earthworms, snails, slugs, insects, which they hunt, attack and capture using physical force and the adhesive and digestive properties of their mucus that dissolve their prey. They feed through a muscular and eversible (able to be turned inside out) pharynx located in ventral side of the body. The pharynx is an extensible tube-like mouth, it bears a complex muscular coat that specializes as a penetration organ for those planarians that feed on arthropods; or as a grasping organ for those planarians that feed on other soft bodied invertebrates such as earthworms.
They lack water-retaining mechanisms and are therefore very sensitive to humidity variations of their environment hence they are normally found in damp shady places during the day. At night they venture into open areas with high humidity.

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. 

Images of some flatworms found in New Zealand. at http://soilbugs.massey.ac.nz/gallery/flatworms.html