Terricola
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 Geoplana burmeisteri Schultze & Mueller, 1857, a typical Geoplanidae from the atlantic rainforests of southern Brazil
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The Suborder Terricola or commonly called Land planarians (Platyhelminthes, Tricladida, Terricola) is one unstudied but not least important group of rare and delicate flatworms that belong to the soil ecosystem[1]. They range between 1 and 20 cm in size and are successful 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[2]. They lack water retaining mechanisms and are therefore very sensible to humidity variations of their environment. Because of their limited biology and sensible ecological requirements some species have been proposed as indicators of the conservation state of their habitats[3][4]. As they are animals with low vagility and with very specific habitat requirements, they can be also used for accurately determining the distribution of biogeographic zones. Today the fauna of these fragile animals is being used to select conservation priorities in the Atlantic rainforest in southern Brazil.
The suborder Terricola is composed of three families: the family Rhychodemidae which is the oldest family and is characterized by having only two eyes in the anterior end of the body; the Bipalidae family, which comprehends Asiatic species that share and half circle head shape. And the most modern family of terrestrial flatworms, the Geoplanidae, which gathers land planarians from south America and Oceania. Despite there are over 820 known species in the world, the diversity of land planarians is still at its beginning, because the few number of researchers interested in this group.
Feeding and Predatory Behavior[5]
“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 eversible pharynx located in ventral side of the body. The pharynx is an extendible 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.
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: a) Some species of land planarians have become invasive pest species, The New Zealand flatworm, Artioposthia triangulata, and the Australian flatworm, Caenoplana alba, have been introduced in the British Isles and today are considered pest species since they prey upon earthworms and may affect soil structure its fertility. b) A species of land planarian, Platydemus manokwari has been used as a biological control of the introduced giant African snail Achatina fulica in Hawaii, Maladives, Irian Jaya, and Guam. Some Land planarians show real 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 its 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 registered in land planarians.
 Geoplana ladislavii Graff, 1899, From a garden in Porto Alegre, southern Brazil. |
 Unknown Geoplaninae from Valdivian Rainforest in southern Chile. |
 Pseudogeoplana reticulata Graff, 1899,from Valdivian Rainforest in southern Chile. |
[edit] Reference
- ^ Winsor, L.; Johns, P.M. & Yeates, G.W. 1998. Introduction, and ecological and systematic background, to the Terricola (Tricladida). Pedobiologia 42: 389-404.
- ^ Ogren, R.E. 1995. Predation behaviour of land planarians. Hydrobiologia 305: 105-111.
- ^ Sluys, R. 1999. Global diversity of land planarians (Platyhelminthes, Tricladida, Terricola): a new indicator-taxon in biodiversity and conservation studies. Biodiversity and Conservation. 8: 1663-1681.
- ^ Carbayo, F.; Leal-Zanchet, A.M & Vieira, E.M. 2002. Terrestrial flatworm (Platyhelminthes: Tricladida: Terricola) diversity vs. man-induced disturbance in a subtropical rainforest from Southern Brazil. Biodiversity and Conservation 11: 1091-1104
- ^ Ogren, R.E. 1995. Predation behaviour of land planarians. Hydrobiologia 305: 105-111.
