Geoplanidae

Geoplanidae
Obama burmeisteri from the Atlantic rainforests of southern Brazil
Scientific classification
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Rhabditophora
Order: Tricladida
Suborder: Continenticola
Family: Geoplanidae
Stimpson, 1857
Subfamilies[1]

Geoplanidae is a family of flatworms known commonly as land planarians or land flatworms.[2]

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.[3] 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.[4][5] 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 ecozones. Today the fauna of these animals is being studied to select conservation priorities in the Atlantic rainforest in Brazil.[6]

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. This species has been found in Europe (France) in 2013 for the first time,[7] and in 2015 in New Caledonia, Wallis and Futuna Islands, Singapore, Solomon Islands, Puerto Rico (first record in the Caribbean), and Florida, USA.[8]

Description

Land planarians are distinguished from their marine and freswhater 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.[9] At first they may be confused with slugs or leeches,[10] but they lack the anterior tentacles of slugs and the segmentation of leeches.

The most distinguishing feature that characterizes land planarians is the presence of a creeping sole, a highly ciliated region on the ventral epidermis that helps them to creep over the substrate.[11] 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.[12]

Anatomy

Epidermis

The epidermis of land planarians is composed by a simple epithelium 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.[9] 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 rhabdites. Rhabditogen cells are very numerous on the dorsal epidermis, but rare on the ventral side.[9]

Nervous System

The nervous system of land planarians has the longitudinal nerve cords reduced to one ventral pair that is located much more deeper in the body when compared to other triclads. These ventral cords are usually connected by many comissures, so that they fuse into a single ventral nerve plate.[11] 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.[11]

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.[13]

Diversity

The family Geoplanidae is composed of four subfamilies:

Although there are over 830 known species of Geoplanidae in the world,[14] the diversity of land planarians is still poorly known.

Habitat

Polycladus gayi from the Valdivian rainforests of southern Chile

Most species of land planarians live at the soil of forests, especially in the leaf litter layer, but some may inhabit galleries constructed by other invertebrates or be found on vegetation, such as bromeliads.[15] Despite being sensitive do dehydration, some species are well adapted to considerably dry environments, such as savannas.[16]

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.[17]

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 number of introduced land planarian species greatly surpass the number of described native species.[18]

Feeding and predatory behavior

A group of land planarians of the species Endeavouria septemlineata feeding on a land snail, Bradybaena similaris

Land planarians are carnivorous and most species are active predators, but some are mainly scavengers.[19]

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.[3]

As part of the soil ecosystem, land planarians feed mainly on other invertebrates, such as earthworms, snails, slugs, nemerteans, velvet worms, woodlice, millipedes, insects and arachnids.[20][21] Some may even feed on other land planarians.[22]

Some species of land planarians have become invasive pest species. The New Zealand flatworm Arthurdendyus triangulatus and the Australian 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.[23][24] Another species, Platydemus manokwari, has been used as an agent of biological pest control of the introduced giant African snail Achatina fulica in Hawaii, the Maldives, Irian Jaya, and Guam, but has become an even worst pest and today threatens several native snail populations in the Pacific.[25]

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.[26][27] 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

Assorted land planarians from Southeast Asia

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, a family of freshwater planarians (at that time part of the suborder Paludicola).[1] 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[1] presents the current classification of planarians:

Tricladida

Maricola

Cavernicola


Continenticola
Planarioidea

Planariidae

Kenkiidae

Dendrocoelidae




Geoplanoidea

Dugesiidae

Geoplanidae






In the former suborder Terricola, land planarians were separated into three families according to morphological features:[28][29]

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.[30] The old subfamilies Caenoplaninae and Pelmatoplaninae have been included as tribes Caenoplanini and Pelmatoplanini inside Rhynchodeminae.[1] Note that Spathula and Romankenkius belong to the Dugesiidae family. Their relocation inside Geoplanidae needs further investigation.[30]

Geoplanoidea

Dugesiidae


Geoplanidae

Bipaliinae


Geoplaninae

Caenoplaninae

Rhynchodeminae

Microplaninae

(Spathula + Romankenkius)






References

  1. 1 2 3 4 Sluys, R.; Kawakatsu, M.; Riutort, M.; Baguñà, J. (2009). "A new higher classification of planarian flatworms (Platyhelminthes, Tricladida)". Journal of Natural History. 43 (29–30): 1763–1777. doi:10.1080/00222930902741669.
  2. ↑ Winsor, L., P. M. Johns, and G. M. Yeates. 1998. Introduction, and ecological and systematic background, to the Terricola (Tricladida). Pedobiologia 42(5-6), 389-404.
  3. 1 2 Ogren, R. E. (1995). "Predation behaviour of land planarians". Hydrobiologia. 305: 105–111. doi:10.1007/BF00036370.
  4. ↑ Sluys, R. (1999). "Global diversity of land planarians (Platyhelminthes, Tricladida, Terricola): a new indicator-taxon in biodiversity and conservation studies". Biodiversity and Conservation. 8 (12): 1663–1681. doi:10.1023/A:1008994925673.
  5. ↑ Carbayo, F.; Leal-Zanchet, A. M.; Vieira, E. M. (2002). "Terrestrial flatworm (Platyhelminthes: Tricladida: Terricola) diversity versus man-induced disturbance in an ombrophilous forest in southern Brazil". Biodiversity and Conservation. 11 (6): 1091–1104. doi:10.1023/A:1015865005604.
  6. ↑ Álvarez-Presas, M.; Sánchez-Garcia, A.; Carbayo, F.; Rozas, J.; Riutort, M. (2014). "Insights into the origin and distribution of biodiversity in the Brazilian Atlantic forest hot spot: a statistical phylogeographic study using a low-dispersal organism". Heredity. 112: 656–665. doi:10.1038/hdy.2014.3.
  7. ↑ Justine, Jean-Lou; Winsor, Leigh; Gey, Delphine; Gros, Pierre; Thévenot, Jessica (2014). "The invasive New Guinea flatworm Platydemus manokwari in France, the first record for Europe: time for action is now.". PeerJ. 2: e297. doi:10.7717/peerj.297. PMC 3961122Freely accessible. PMID 24688873.
  8. ↑ Justine, Jean-Lou; Winsor, Leigh; Barrière, Patrick; Fanai, Crispus; Gey, Delphine; Han, Andrew Wee Kien; La Quay-Velázquez, Giomara; Lee, Benjamin Paul Yi-Hann; Lefevre, Jean-Marc; Meyer, Jean-Yves; Philippart, David; Robinson, David G.; Thévenot, Jessica; Tsatsia, Francis (2015). "The invasive land planarianPlatydemus manokwari(Platyhelminthes, Geoplanidae): records from six new localities, including the first in the USA". PeerJ. 3: e1037. doi:10.7717/peerj.1037. ISSN 2167-8359.
  9. 1 2 3 Seitenfus, Ana Lúcia Ramos; Leal-Zanchet, Ana Maria (2004). "Uma introdução à morfologia e taxonomia de planárias terrestres (Platyhelminthes, Tricladida, Terricola)". Acta Biologica Leopoldensia (in Portuguese). 26 (2): 187–202.
  10. ↑ Schirch, P. F. (1929). "Sobre as planarias terrestres do Brasil". Boletim do Museu Nacional (in Portuguese). 5: 27–38.
  11. 1 2 3 Sluys, Ronald (1989). "Phylogenetic relationships of the triclads (Platyhelminthes, Seriata, Tricladida)". Bijdragen tot de Dierkunde. 59 (1): 3–25.
  12. ↑ von Graff, Ludwig (1899). Monographie der Turbellarien. II. Tricladida Terricola (in German). Leipzig: Engelmann. p. 540.
  13. ↑ Hyman, Libbie H. (1951). The invertebrates. II. Platyhelminthes and Rhynchocoela. New York: McGraw-Hill. p. 550.
  14. ↑ Schockaert, E. R., et al. 2008. Global diversity of free living flatworms (Platyhelminthes, "Turbellaria") in freshwater. Hydrobiologia 198, 41-48.
  15. ↑ Beauchamp, P. (1913). "Planaires des Broméliacées de Costa Rica Recueillies par Mr C. Picado.". Archives de Zoologie Paris (in French). 51: 41–52.
  16. ↑ Cumming, Meg S. (1995). "Activity patterns of termite-eating land planariansMicroplana termitophaga(Platyhelminthes: Tricladida)". Journal of Zoology. 237 (4): 531–542. doi:10.1111/j.1469-7998.1995.tb05013.x. ISSN 0952-8369.
  17. ↑ Ogren, Robert E. (1955). "Ecological Observations on the Occurrence of Rhynchodemus, a Terrestrial Turbellarian". Transactions of the American Microscopical Society. 74 (1): 54. doi:10.2307/3223842. ISSN 0003-0023.
  18. ↑ Jones, H.D.; Boag, B. (2007). "The distribution of New Zealand and Australian terrestrial flatworms (Platyhelminthes: Turbellaria: Tricladida: Terricola) in the British Isles—the Scottish survey and MEGALAB WORMS". Journal of Natural History. 30 (7): 955–975. doi:10.1080/00222939600770511. ISSN 0022-2933.
  19. ↑ McDonald, Jillian C.; Jones, Hugh D. (2007). "Abundance, reproduction, and feeding of three species of British terrestrial planarians: Observations over 4 years". Journal of Natural History. 41 (5-8): 293–312. doi:10.1080/00222930701219149. ISSN 0022-2933.
  20. ↑ Boll, Piter Kehoma; Leal-Zanchet, Ana Maria (2014). "Predation on invasive land gastropods by a Neotropical land planarian". Journal of Natural History. 49 (17-18): 983–994. doi:10.1080/00222933.2014.981312. ISSN 0022-2933.
  21. ↑ Prasniski, Maria E. T.; Leal-Zanchet, Ana M. (2009). "Predatory behavior of the land flatworm Notogynaphallia abundans (Platyhelminthes: Tricladida)". Zoologia (Curitiba). 26 (4): 606–612. doi:10.1590/S1984-46702009005000011. ISSN 1984-4670.
  22. ↑ Boll, Piter K.; Rossi, Ilana; Amaral, Silvana V.; Leal-Zanchet, Ana (2015). "A taste for exotic food: Neotropical land planarians feeding on an invasive flatworm". PeerJ. 3: e1307. doi:10.7717/peerj.1307. ISSN 2167-8359.
  23. ↑ Santoro, Giulio; Jones, Hugh D. (2001). "Comparison of the earthworm population of a garden infested with the Australian land flatworm (Australoplana sanguinea alba) with that of a non-infested garden". Pedobiologia. 45 (4): 313–328. doi:10.1078/0031-4056-00089. ISSN 0031-4056.
  24. ↑ Murchie, Archie K.; Gordon, Alan W. (2012). "The impact of the 'New Zealand flatworm', Arthurdendyus triangulatus, on earthworm populations in the field". Biological Invasions. 15 (3): 569–586. doi:10.1007/s10530-012-0309-7. ISSN 1387-3547.
  25. ↑ Sugiura, Shinji; Yamaura, Yuichi (2008). "Potential impacts of the invasive flatworm Platydemus manokwari on arboreal snails". Biological Invasions. 11 (3): 737–742. doi:10.1007/s10530-008-9287-1. ISSN 1387-3547.
  26. ↑ Fiore, C.; Tull, J. L.; Zehner, S.; Ducey, P. K. (2004). "Tracking and predation on earthworms by the invasive terrestrial planarian Bipalium adventitium (Tricladida, Platyhelminthes)". Behavioural Processes. 67 (3): 327–334. doi:10.1016/j.beproc.2004.06.001. PMID 15518983.
  27. ↑ Iwai, N.; Sugiura, S.; Chiba, S. (2010). "Prey-tracking behavior in the invasive terrestrial planarian Platydemus manokwari (Platyhelminthes, Tricladida)". Naturwissenschaften. 97 (11): 997–1002. doi:10.1007/s00114-010-0717-4. PMID 20853096.
  28. ↑ Ogren, R. E. and Kawakatsu, M. (1988) "Index to the species of the family Rhynchodemidae (Turbellaria, Tricladida, Terricola) Part I: Rhynchodeminae". Bulletin of Fuji Women's College 26 (2): 39-91.
  29. ↑ Ogren, R. E. and Kawakatsu, M. (1991) "Index to the species of the family Geoplanidae (Turbellaria, Tricladida, Terricola) Part II: Caenoplaninae and Pelmatoplaninae".: Bulletin of Fuji Women's College 29 (2): 35-58.
  30. 1 2 Álvarez-Presas, M.; Baguñà, J.; Riutort, M. (2008). "Molecular phylogeny of land and freshwater planarians (Tricladida, Platyhelminthes): From freshwater to land and back". Molecular Phylogenetics and Evolution. 47 (2): 555–568. doi:10.1016/j.ympev.2008.01.032. PMID 18359250.
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