| Geoplanidae | |
|---|---|
| Geoplana burmeisteri Schultze & Mueller, 1857, a typical Geoplanidae from the Atlantic rainforests of southern Brazil | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Class: | Turbellaria |
| Subclass: | Archoophora |
| Order: | Tricladida Lang, 1884 |
| Family: | Geoplanidae Stimpson, 1857 |
| Subfamilies[1] | |
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The Family Geoplanidae, common name Land planarians (Platyhelminthes, Tricladida, Geoplanidae) is an understudied but important group of flatworms that belong to the soil ecosystem.[2]
These flatworms range between 1 and 20 cm in size, and are predators of other invertebrates such as earthworms, snails, slugs, insects and chelicerates, which they hunt for, attack and capture using physical force and the adhesive and digestive properties of their mucus.[3] They lack water-retaining mechanisms and are therefore very sensitive to humidity variations of their environment.
Because of their limited ecological requirements, some species have been proposed as indicators of the conservation state of their habitats.[4][5] They are generally animals with low vagility and with very specific habitat requirements, so they can be also used to accurately determine the distribution of biogeographic zones. Today the fauna of these mostly rather fragile animals is being used to select conservation priorities in the Atlantic rainforest in southern Brazil.
At the other extreme, one species in this family, Platydemus manokwari has become an invasive species in both disturbed and wild habitats in the Pacific Islands, and has damaged the endemic land snail faunas.
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The Family Geoplanidae is composed of four subfamilies:
Although there are over 820 known species of Geoplanidae in the world, the diversity of land planarians is still very poorly known, because there are so few number of researchers investigating this group of animals.
"If contact with food is made, and the planarian is ready to feed, arousal and predatory behaviour will occur" (Neck, 1987)
Despite their delicate aspect these terrestrial flatworms are voracious predators. All planarians feed through a muscular and reversible pharynx located in ventral side of the body. The pharynx is an extensible tube-like mouth, it bears complex muscular coat that specialized as a penetration organ for those planarians that feed on arthropods; or as a grasping for those planarians that feed on other soft bodied invertebrates such as earthworms. All pharynxes are equipped with glandular secretions that externally digest and dissolve their prey.[3]
As part of the soil ecosystem land planarians feed mainly on other invertebrates such as earthworms, slugs and snails, termites, isopods, and other land planarians. Two facts prove the effectiveness of land planarians as predators:
Some land planarians show hunting behaviour, using chemical signals to detect their prey. Most land planarians have chemical sensory organs in the anterior part of the body, such as sensory pits and epidermal folds which serve as chemical radars for detecting their food. The mucus trails from the slime of slugs, snails and other planarians orient planarians towards their prey.
Different species of land planarians use different techniques for capturing and immobilizing their prey, such as entrapment with sticky mucus and immobilization by physical force.
Cannibalism has been observed in land planarians.