Geoplanidae is a family of

flatworm Platyhelminthes (from the Greek language, Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a Phylum (biology), phylum of relatively simple bilaterian, Segmentation (biology), ...

s known commonly as land planarians or land flatworms. These flatworms are mainly predators of other invertebrates, which they hunt, attack and capture using physical force and the adhesive and digestive properties of their mucus. They lack water-retaining mechanisms and are therefore very sensitive to humidity variations of their environment. Because of their strict ecological requirements, some species have been proposed as indicators of the conservation state of their habitats. They are generally animals with low vagility (dispersal ability) and with very specific habitat requirements, so they can be also used to accurately determine the distribution of

biogeographic realm A biogeographic realm is the broadest biogeography, biogeographic division of Earth's land surface, based on distributional patterns of terrestrial animal, terrestrial organisms. They are subdivided into bioregions, which are further subdivid ...

s. Today the fauna of these animals is being studied to select conservation priorities in the Atlantic rainforest in Brazil. At the other extreme, one species in this family, ''

Platydemus manokwari ''Platydemus manokwari'', also known as the New Guinea flatworm, is a species of large predatory land flatworm. Native to New Guinea, it has been accidentally introduced to the soil of many countries, including the United States. It was als ...

'' has become an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

in both disturbed and wild habitats in the

Pacific Islands The Pacific islands are a group of islands in the Pacific Ocean. They are further categorized into three major island groups: Melanesia, Micronesia, and Polynesia. Depending on the context, the term ''Pacific Islands'' may refer to one of several ...

, and has damaged the endemic land snail fauna. This species has been found in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

(

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

) in 2013 for the first time, and in 2015 in

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

Wallis and Futuna Wallis and Futuna, officially the Territory of the Wallis and Futuna Islands (), is a French island territorial collectivity, collectivity in the Oceania, South Pacific, situated between Tuvalu to the northwest, Fiji to the southwest, Tonga t ...

Islands,

Singapore Singapore, officially the Republic of Singapore, is an island country and city-state in Southeast Asia. The country's territory comprises one main island, 63 satellite islands and islets, and one outlying islet. It is about one degree ...

Solomon Islands Solomon Islands, also known simply as the Solomons,John Prados, ''Islands of Destiny'', Dutton Caliber, 2012, p,20 and passim is an island country consisting of six major islands and over 1000 smaller islands in Melanesia, part of Oceania, t ...

Puerto Rico ; abbreviated PR), officially the Commonwealth of Puerto Rico, is a Government of Puerto Rico, self-governing Caribbean Geography of Puerto Rico, archipelago and island organized as an Territories of the United States, unincorporated territo ...

(first record in the Caribbean), and

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, USA.

Description

Land planarians are distinguished from their marine and freshwater relatives by their terrestrial habits, as well as by morphological distinctions. Some species have dull colors, including shades of brown and grey, that make them inconspicuous in their environment, but most species are marked by very colorful patterns. At first they may be confused with

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

s or

leech Leeches are segmented parasitism, parasitic or Predation, predatory worms that comprise the Class (biology), subclass Hirudinea within the phylum Annelida. They are closely related to the Oligochaeta, oligochaetes, which include the earthwor ...

es, but they lack the anterior tentacles of slugs and the segmentation of leeches. Their size vary greatly, from a few millimeters in length to about one meter. The most distinguishing feature that characterizes land planarians is the presence of a creeping sole, a highly ciliated region on the ventral

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

that helps them to creep over the substrate. The creeping sole may be wide and flat, occupying most of the ventral surface, or narrow and pronounced, being easily distinguished from the rest of the ventral surface.

Anatomy

Epidermis

The

of land planarians is composed by a simple

epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

of cubic or columnar cells. The cells are ciliated only on a ventral region, called ''creeping sole'', which the animal uses to glide over surfaces. Numerous secretory cells open throughout the epidermis, the most characteristic ones being the rhabditogen cells, which produce a secretion in the form of small rod-like structures, the

rhabdite Rhabdites (from Greek, ''rhabdos'', rod) are rodlike structures in the cells of the epidermis or underlying parenchyma in certain turbellarians, and in the epidermis of nemertea Nemertea is a phylum of animals also known as ribbon worms or ...

s. Rhabditogen cells are very numerous on the dorsal epidermis, but rare on the ventral side.

Nervous system

The

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

of land planarians has the longitudinal nerve cords reduced to one ventral pair that is located much deeper in the body than in other triclads. These ventral cords are usually connected by many comissures, so that they fuse into a single ventral nerve plate. Additionally, land planarians have a highly developed ventral nerve plexus just below the epidermis that is probably associated to the presence of a creeping sole. Contrary to aquatic planarians, land planarians do not have a distinct brain, i.e., there is no clear frontal cluster of nerve cells other than the ventral nerve plate.

Diversity

The family Geoplanidae is composed of five subfamilies: *

Bipaliinae Bipaliinae is a subfamily of land planarians found mainly in Madagascar, the Indian subcontinent and Southeast Asia, although some species have been introduced worldwide. Description The subfamily Bipaliinae is characterized by having a sem ...

Geoplaninae Geoplaninae is a subfamily of land planarians endemic to the Neotropical region. Members of this family are sometimes referred to as the Neotropical land planarians. However, one species, '' Obama nungara'' has been introduced in Europe. Descri ...

Microplaninae Microplaninae is a subfamily of land planarians. Description The subfamily Microplaninae was defined by Ogren and Kawakatsu (1988)Ogren, R. E. and Kawakatsu, M. (1988). ''Index to the species of the family Rhynchodemidae (Turbellaria, Tricladida, ...

Rhynchodeminae Rhynchodeminae is a subfamily of land planarians with a worldwide distribution. Phylogeny and systematics Based on morphological evidence, especially the presence of a single pair of eyes, the subfamily Rhynchodeminae initially encompassed only ...

Timyminae ''Timyma'' is a genus of land planarians from Chile. It is the sole genus of the subfamily Timyminae. Description The genus ''Timyma'' includes planarians of elongate body and spatula-like anterior end. Although most land planarians native fro ...

Although there are over 830 known species of Geoplanidae in the world, the diversity of land planarians is still poorly known. The highest diversity occurs in tropical forests in South America, Asia and Australia. Europe and North America are relatively species-poor, while the diversity of Africa may be as high as that of other tropical regions, but is highly understudied.

Habitat

Most species of land planarians live at the soil of forests, especially in the

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituen ...

layer, but some may inhabit galleries constructed by other invertebrates or be found on vegetation, such as

bromeliad The Bromeliaceae (the bromeliads) are a Family (biology), family of monocot flowering plants of about 80 genera and 3700 known species, native mainly to the Tropics, tropical Americas, with several species found in the American subtropics and on ...

s. Despite being sensitive to dehydration, some species are well adapted to considerably dry environments, such as

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

s. During unfavorable conditions, such as dry seasons, land planarians tend to seek shelter by burrowing in the soil or building a cyst composed of soil particles united by mucus. Some species are well adapted to human-disturbed environments and many of those have been introduced in areas outside of their native range. In some localities, such as the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, the number of introduced land planarian species greatly surpass the number of described native species.

Feeding and predatory behavior

Land planarians are carnivorous and most species are active predators, but some are mainly scavengers. All planarians feed through a muscular and eversible pharynx located slightly posteriorly to the middle of the body length and opening through a ventral mouth. The pharynx is an extensible tube-like organ bearing a complex muscular coat. It 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. All geoplanidae 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

earthworm An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass, depending on the author) Oligochaeta. In classical systems, they we ...

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

nemertea Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of about 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. ...

ns,

velvet worm Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus''), is a phylum of e ...

woodlice Woodlice are terrestrial isopods in the suborder Oniscidea. Their name is derived from being often found in old wood, and from louse, a parasitic insect, although woodlice are neither parasitic nor insects. Woodlice evolved from marine isopods ...

millipede Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s and

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

s. Some may even feed on other land planarians. Some species of land planarians have become invasive pest species. The New Zealand flatworm '' Arthurdendyus triangulatus'' and the

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

n flatworm '' Australoplana sanguinea alba'' have been introduced in the British Isles and are considered to be pest species because they prey upon earthworms and thus may negatively affect soil structure and fertility. Another species, ''

'', has been used as an agent of

biological pest control Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or ot ...

of the introduced giant African snail ''

Achatina fulica ''Lissachatina fulica'' is a species of large land snail that belongs in the subfamily Achatininae of the family Achatinidae. It is also known as the giant African land snail. It shares the common name "giant African snail" with other species of ...

'' in

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, the

Maldives The Maldives, officially the Republic of Maldives, and historically known as the Maldive Islands, is an Archipelagic state, archipelagic country in South Asia located in the Indian Ocean. The Maldives is southwest of Sri Lanka and India, abou ...

Irian Jaya New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is separated from Austral ...

, and

Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...

, but has become an even worse pest and today threatens several native snail populations in the Pacific. 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 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.

Phylogeny and systematics

Until very recently, land planarians were classified as a suborder within Tricladida, named Terricola. However, recent phylogenetic studies revealed that they are actually the sister-group of

Dugesiidae Dugesiidae is a family of freshwater planarians distributed worldwide (except Antarctica). The type genus is ''Dugesia ''Dugesia'' is a genus of freshwater planarians in the family Dugesiidae triclads and the type genus of this family. Thes ...

, a family of freshwater planarians (at that time part of the suborder Paludicola). The most recent classification puts both land and freshwater planarians within a single suborder called Continenticola, with land planarians forming a single family, Geoplanidae. The following phylogenetic supertree after Sluys et al., 2009 presents the current classification of planarians: In the former suborder Terricola, land planarians were separated into three families according to morphological features: * Bipaliidae: head expanded in a spatula-like shape and multiple eyes; * Rhynchodemidae: non-expanded head and a single pair of eyes. It included two subfamilies: Rhynchodeminae, with subepithelial longitudinal muscular fibers grouped into large bundles, and Microplaninae, with weaker subepithelial longitudinal muscular fibers not forming bundles; * Geoplanidae: non-expanded head and multiple eyes. It included three subfamilies: Geoplaninae, with dorsal testicles and strong subepithelial longitudinal muscles, Caenoplaninae, with ventral testicles and strong subepithelial longitudinal muscles, and Pelmatoplaninae, with ventral testicles and weak subepithelial longitudinal muscles. Recent phylogenetic analyses, however, revealed that Rhynchodeminae and Microplaninae are not closely related and that Caenoplaninae is closer to Rhynchodeminae than to Geoplaninae. The current classification of land planarian subfamilies is shown in the following phylogenetic tree after Álvarez-Presas et al., 2008. The old subfamilies Caenoplaninae and Pelmatoplaninae have been included as tribes Caenoplanini and Pelmatoplanini inside Rhynchodeminae. Note that ''Spathula'' and ''Romankenkius'' belong to the family

. Their relocation inside Geoplanidae needs further investigation.

Image gallery

File:Bipalium adventitium close up.jpg, ''

Bipalium adventitium ''Bipalium adventitium'', the wandering broadhead planarian, is a land planarian in the subfamily Bipaliinae. It has been accidentally introduced in the United States, where it is considered invasive. Appearance Most adult individuals of ''B. a ...

'' close up under a rock, North California, USA. File:Geoplana ladislavi.jpg, ''

Obama ladislavii ''Obama ladislavii'' is a species of Brazilian land planarian in the subfamily Geoplaninae. It is one of the most common land planarians in human-disturbed environments in southern Brazil and is easily identifiable by the green color of its dorsu ...

'' from a garden in Porto Alegre, southern Brazil. File:Cephaloflexa araucariana.JPG, '' Cephaloflexa araucariana'' from the

São Francisco de Paula National Forest SAO or Sao may refer to: Places * Sao civilisation, in Middle Africa from 6th century BC to 16th century AD * Sao, a town in Boussé Department, Burkina Faso * Serb Autonomous Regions (''Srpska autonomna oblast'', SAO), during the breakup of Y ...

, southern Brazil. File:Luteostriata ernesti.JPG, '' Luteostriata ernesti'' in the São Francisco de Paula National Forest. File:Notogynaphallia plumbea.jpg, ''Notogynaphallia plumbea'' from an

Araucaria moist forest The Araucaria moist forests, officially classified as mixed ombrophilous forest (Portuguese: "Floresta Ombrófila Mista") in Brazil, are a montane subtropical moist forest ecoregion. The forest ecosystem is located in southern and in few areas of ...

Paraná Paraná, Paranã or Parana may refer to: Geology * Paraná Basin, a sedimentary basin in South America Places In Argentina *Paraná, Entre Ríos, a city * Paraná Department, a part of Entre Ríos Province In Brazil *Paraná (state), a state ...

, Brazil. File:Platyhelminthes, Tricladida, Terricola, Atlantic forest, northern littoral of Bahia, Brazil (14617707721).jpg, Unidentified land planarian from

Bahia Bahia () is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (state), São Paulo, Mina ...

, Brazil. File:Geoplaninae.jpg, Unidentified land planarian from the Valdivian Rainforest in

southern Chile Southern Chile is an informal geographic term for any place south of the capital city, Santiago, or south of Biobío River, the mouth of which is Concepción, about {{convert, 200, mi, km, sigfig=1, order=flip south of Santiago. Generally citie ...

. File:Pseudogeoplana reticulata.jpg, ''Pseudogeoplana reticulata'' from the Valdivian Rainforest. File:Caenoplana coerulea.jpg, ''

Caenoplana coerulea ''Caenoplana coerulea'', known as the blue planarian or blue garden flatworm is a species of Geoplanidae, land planarian. Description This is a long narrow flatworm, which is shiny black or dark brown on the upper surface, and mid-blue undernea ...

'', the blue planarian. File:New Zealand flatworm 2.JPG, '' Arthurdendyus triangulatus'', the New Zealand flatworm. File:Peerj-297-fig-1 Platydemus manokwari.png, ''

'' in

. File:Rhynchodemus sylvaticus.jpg, ''Rhynchodemus sylvaticus'' in the Iberian Peninsula. File:Microplana sp2.JPG, ''Microplana robusta'' in

Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...

. File:Diversibipalium multilineatum from Italy - Fig 1 a - Body.png, ''

Diversibipalium multilineatum ''Diversibipalium multilineatum'' is a species of large predatory land flatworm. The species is native to Japan. Makino N, Shirasawa Y (1983). Morphological and ecological comparison with two new species of elongated-slender land planarians hav ...

'' in

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

. File:Bipaliinae 2.jpg, Species of subfamily Bipaliinae in Sarawak,

Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...

. File:Diversibipalium rauchi.png, ''Diversibipalium rauchi'' in Thomson Nature Park, Singapore. File:Bipaliumjavanum15062024.jpg, Bipalium Javanum in

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

References

External links

Video of juvenile Land Planarian in Borneo
{{Taxonbar, from=Q3112410 Taxa named by William Stimpson Platyhelminthes families