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Catenulida

provided by wikipedia EN

Catenulida is an order of flatworms in the classical classification, or a class of flatworms in a phylogenetic approach.[2] They are relatively small free-living flatworms, inhabiting freshwater and marine environments. There are about 100 species described worldwide, but the simple anatomy makes species distinction problematic.[2]

Description

The anatomy of catenulids is simple and lacks hard parts. The mouth is located anteriorly and connects to a simple pharynx and a simple intestine that forms a ciliated sac. They possess two pairs of nerve cords and often a statocyst, as well as a single protonephridium.[2]

The gonads are unpaired. Unusually, the male gonopore opens on the dorsal surface of the animal, above the pharynx, while the female reproductive system lacks any of the usual ducts and related structures found in other flatworms. The sperm is nonmobile and lacks flagella or cilia.[2] Asexual reproduction by paratomy is common, and it usually leads to a chain of organisms (zooids), hence the name, from Latin catenula, small chain.[2]

Members of the symbiotic genus Paracatenula lack a digestive tract, and instead use intracellular chemoautotrophic bacterial symbionts for their nutrition.[3][4]

Ecology

All catenulids are aquatic, benthic animals. Most of them live in freshwater, being usually very abundant in mires, ponds, streams and moist terrestrial habitats. A small number of species are known to live in the sea.[5]

The diet of most catenulids consists of small invertebrates and algae that they capture from the water column.[6] Others, such as those of the genus Paracatenula use chemoautotrophic bacterial symbionts that live inside their cells as a food source.[3]

Phylogeny

The monophyly of Catenulida is supported by molecular studies and by at least 3 synapomorphies: the unpaired protonephridium, the unpaired and anterodorsally located testis and the nonmobile sperm.[7]

Although there are no known synapomorphies connecting Catenulida to other flatworms (Rhabditophora), molecular studies indicate that they are sister-groups. All characters common to both clades, such as the internal fertilization and the simple gut with a single opening, are found in other groups as well.[2]

References

  1. ^ Artois, T.; Tyler, S. (2015). Catenulida. In: Tyler, S., Artois, T.; Schilling, S.; Hooge, M.; Bush, L.F. (eds) (2006-2017). World list of Platyhelminthes. Accessed through: World Register of Marine Species at [1] on 2017-02-14
  2. ^ a b c d e f Larsson, K.; Jondelius, U. (2008). "Phylogeny of the Catenulida and support for Platyhelminthes". Organisms Diversity & Evolution. 8 (5): 378–387. doi:10.1016/j.ode.2008.09.002..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  3. ^ a b Leisch, N.; Dirks, U.; Gruber-Vodicka, H. R.; Schmid, M.; Sterrer, W.; Ott, J. A. (2011). "Microanatomy of the trophosome region of Paracatenula cf. polyhymnia (Catenulida, Platyhelminthes) and its intracellular symbionts". Zoomorphology. 130 (4): 261–271. doi:10.1007/s00435-011-0135-y. PMC 3213344. PMID 22131640.
  4. ^ Gruber-Vodicka, H. R.; Dirks, U.; Leisch, N.; Baranyi, C.; Stoecker, K.; Bulgheresi, S.; Heindl, N. R.; Horn, M.; Lott, C.; Loy, A.; Wagner, M.; Ott, J. (27 June 2011). "Paracatenula, an ancient symbiosis between thiotrophic Alphaproteobacteria and catenulid flatworms". Proceedings of the National Academy of Sciences. 108 (29): 12078–12083. doi:10.1073/pnas.1105347108. PMC 3141929. PMID 21709249.
  5. ^ Larsson, K.; Ahmadzadeh, A.; Jondelius, U. (2008). "DNA taxonomy of Swedish Catenulida (Platyhelminthes) and a phylogenetic framework for catenulid classification". Organisms Diversity & Evolution. 8 (5): 399–412. doi:10.1016/j.ode.2008.09.003. ISSN 1439-6092.open access publication – free to read
  6. ^ Núñez-Ortiz, Alma R.; Nandini, Sarma; Nandini, S.S.S. (2016). "Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)". Journal of Limnology. 75 (s1): 48–55. doi:10.4081/jlimnol.2016.1369. ISSN 1723-8633.open access publication – free to read
  7. ^ Boll, Piter Kehoma; Rossi, Ilana; Amaral, Silvana Vargas do; Oliveira, Simone Machado de; Müller, Eliara Solange; Lemos, Virginia Silva; Leal-Zanchet, Ana Maria (2013). "Platyhelminthes ou apenas semelhantes a Platyhelminthes? Relações filogenéticas dos principais grupos de turbelários". Neotropical Biology and Conservation (in Portuguese). 8 (1). doi:10.4013/nbc.2013.81.06. ISSN 2236-3777.open access publication – free to read
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Catenulida: Brief Summary

provided by wikipedia EN

Catenulida is an order of flatworms in the classical classification, or a class of flatworms in a phylogenetic approach. They are relatively small free-living flatworms, inhabiting freshwater and marine environments. There are about 100 species described worldwide, but the simple anatomy makes species distinction problematic.

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Classification

provided by World Register of Marine Species
The classification used here is a compromise between the more traditional taxonomy of Neodermata vs. the turbellarians. Yet it reflects the fact that Neodermata is within free-living flatworms (i.e. turbellaria are paraphyletic). It mentions all traditional taxa that are found in phylogenetic studies (e.g. Laumer et al., 2015). Many of the "in-between" higher level taxa (such as Trepaxonemata etc.) are no longer in WoRMS (probably more user friendly that way). This also means an asymmetry between turbellarians (nine ordines) and Neodermata (superclass with three classes).
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Artois, Tom [email]