Rhabdocoela

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Rhabdocoela
Strongylostoma elongatum spinosum.jpg
Strongylostoma elongatum spinosum.
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Platyhelminthes
Subphylum: Rhabditophora
Order: Rhabdocoela
Ehrenberg, 1831
Suborders

Rhabdocoela is an order of flatworms in the class Rhabditophora with about 1700 species described worldwide. The order was first described in 1831 by Christian Gottfried Ehrenberg. [1] Most of rhabdocoels are free-living organisms, but some live symbiotically with other animals. [2]

Contents

Description

Although Rhabdocoela is a highly supported group in molecular studies, there is no clear morphological synapomorphy that unites them. All rhabdocoels have a bulbous pharynx, but this is shared with other flatworm groups, such as Neodermata, Lecithoepitheliata and some species of Prolecithophora. [3]

Some possibly identified synapomorphies are found in the ultrastructure of the protonephridial system, but similar constructions exist in other groups. Another possible apomorphy is found in the ultrastructure of the sperm, which has a dense heel on the basal bodies during spermiogenesis, but some groups have lost this feature. [3]

Classification

Rhabdocoels were traditionally classified in two groups, Dalyellioida and Typhloplanoida, although this system was suspected to be artificial. Later, molecular studies have shown that these groups were not monophyletic. [4] One subgroup of Dalyellioida, Fecampiida, does not group within Rhabdocoela, but is closely related to Tricladida and Prolecithophora. The group Kalyptorhynchia, previously a subgroup of Thyphloplanoida, appears to be the sister-group of most other rhabdocoels, which form a clade named Dalytyphloplanida. [3] Recently, a third group, Mariplanellida, was erected based on molecular phylogeny. [5]

Ecology

Most rhabdocoels are freshwater organisms. Some groups, such as typhloplanids, are predators, the main prey being cladocerans. [6] Others feed on algae and may incorporate them in their tissues. [7]

The temnocephalidans all live as ectosymbionts or parasites of other freshwater animals, such as arthropods, mollusks, and turtles. [8]

Related Research Articles

<span class="mw-page-title-main">Flatworm</span> Phylum of soft-bodied invertebrates known as flatworms

The flatworms, flat worms, Platyhelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.

<span class="mw-page-title-main">Turbellaria</span> Class of flatworms

The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from 1 mm (0.039 in) to large freshwater forms more than 500 mm (20 in) long or terrestrial species like Bipalium kewense which can reach 600 mm (24 in) in length. All the larger forms are flat with ribbon-like or leaf-like shapes, since their lack of respiratory and circulatory systems means that they have to rely on diffusion for internal transport of metabolites. However, many of the smaller forms are round in cross section. Most are predators, and all live in water or in moist terrestrial environments. Most forms reproduce sexually and with few exceptions all are simultaneous hermaphrodites.

<span class="mw-page-title-main">Acoelomorpha</span> Phylum of marine, flatworm-like animals

Acoelomorpha is a subphylum of very simple and small soft-bodied animals with planula-like features which live in marine or brackish waters. They usually live between grains of sediment, swimming as plankton, or crawling on other organisms, such as algae and corals. With the exception of two acoel freshwater species, all known Acoelomorphs are marine.

<span class="mw-page-title-main">Catenulida</span> Order of relatively small free-living flatworms

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.

<span class="mw-page-title-main">Dugesiidae</span> Family of flatworms

Dugesiidae is a family of freshwater planarians distributed worldwide. The type genus is Dugesia Girard, 1850.

<span class="mw-page-title-main">Nephrozoa</span> Clade of animals

Nephrozoa is a major clade of bilaterians, divided into the protostomes and the deuterostomes, containing almost all animal phyla and over a million extant species. Its sister clade is the Xenacoelomorpha. The Ambulacraria was formerly thought to be sister to the Xenacoelomorpha, forming the Xenambulacraria as basal Deuterostomes, or basal Bilateria invalidating Nephrozoa and Deuterostomes in earlier studies. The coelom, the digestive tract and excretory organs (nephridia), and nerve cords developed in the Nephrozoa. It has been argued that, because protonephridia are only found in protostomes, they cannot be considered a synapomorphy of this group. This would make Nephrozoa an improper name, leaving Eubilateria as this clade's name.

<span class="mw-page-title-main">Dimarcusidae</span> Family of flatworms

Dimarcusidae is a family of triclads found mostly in freshwater habitats of caves, although at least one species, Rhodax evelinae, occurs in surface waters. Currently the family contains only seven species distributed in five genera, although the total number of species is thought to be much higher.

<span class="mw-page-title-main">Xenacoelomorpha</span> A deep-branching bilaterian clade of animals with a simple body plan

Xenacoelomorpha is a small phylum of bilaterian invertebrate animals, consisting of two sister groups: xenoturbellids and acoelomorphs. This new phylum was named in February 2011 and suggested based on morphological synapomorphies, which was then confirmed by phylogenomic analyses of molecular data.

<span class="mw-page-title-main">Cavernicola (suborder)</span> Suborder of flatworms

Cavernicola is a suborder of planarians found mostly in freshwater habitats of caves, although some species occur on the surface.

<span class="mw-page-title-main">Geoplaninae</span> Subfamily of flatworms

Geoplaninae is a subfamily of land planarians endemic to the Neotropical region. However, one species, Obama nungara has been introduced in Europe.

<i>Obama</i> (genus) Genus of worms

Obama is a genus of land planarians from South America. It contains several species adapted to human-disturbed environments, including the only invasive land planarian native to the Neotropical realm, Obama nungara, which has been accidentally introduced in Europe.

<span class="mw-page-title-main">Reproductive system of planarians</span>

The reproductive system of planarians is broadly similar among different families, although the associated structures can vary in complexity.

<i>Supramontana</i> Genus of flatworms

Supramontana is a genus of land planarians from South America.

<span class="mw-page-title-main">Neodermata</span> Clade of flatworms

Neodermata is a clade of rhabditophoran flatworms containing the parasitic groups Trematoda, Monogenea and Cestoda.

Rhabditophora is a class of flatworms. It includes all parasitic flatworms and most free-living species that were previously grouped in the now obsolete class Turbellaria. Therefore, it contains the majority of the species in the phylum Platyhelminthes, excluding only the catenulids, to which they appear to be the sister group.

<i>Matuxia</i> Genus of flatworms

Matuxia is a genus of land planarians from Brazil.

<span class="mw-page-title-main">Proseriata</span> Order of free-living flatworms in the class Rhabditophora

Proseriata is an order of free-living flatworms in the class Rhabditophora with over 400 species described worldwide.

Fecampiida is an order of flatworms in the class Rhabditophora. It is a considerably recent clade, erected after molecular studies.

<span class="mw-page-title-main">Kalyptorhynchia</span> Suborder of rhabdocoel flatworms

Kalyptorhynchia is a suborder of rhabdocoel flatworms. It contains almost 600 species and has a cosmopolitan distribution.

<span class="mw-page-title-main">Dalytyphloplanida</span> Suborder of flatworms

Dalytyphloplanida is a suborder of rhabdocoel flatworms. It contains about 1000 species and has a cosmopolitan distribution in both marine and freshwater environments, with several groups having comensal or parasitic lifestyles.

References

  1. "WoRMS - World Register of Marine Species - Rhabdocoela". www.marinespecies.org. Retrieved 2022-12-30.
  2. Tessens, Bart; Janssen, Toon; Artois, Tom (2014). "Molecular phylogeny of Kalyptorhynchia (Rhabdocoela, Platyhelminthes) inferred from ribosomal sequence data". Zoologica Scripta. 43 (5): 519–530. doi:10.1111/zsc.12066. ISSN   0300-3256. S2CID   86369823.
  3. 1 2 3 Willems, Wim R.; Wallberg, Andreas; Jondelius, Ulf; Littlewood, David T. J.; Backeljau, Thierry; Schockaert, Ernest R.; Artois, Tom J. (2006). "Filling a gap in the phylogeny of flatworms: relationships within the Rhabdocoela (Platyhelminthes), inferred from 18S ribosomal DNA sequences". Zoologica Scripta. 35 (1): 1–17. doi:10.1111/j.1463-6409.2005.00216.x. hdl: 1942/1609 . ISSN   0300-3256. S2CID   85917387.
  4. Littlewood, D. T. J.; Rohde, K.; Clough, K. A. (1999). "The interrelationships of all major groups of Platyhelminthes: phylogenetic evidence from morphology and molecules". Biological Journal of the Linnean Society. 66 (1): 75–114. doi: 10.1111/j.1095-8312.1999.tb01918.x . ISSN   0024-4066.
  5. Van Steenkiste, Niels W. L.; Leander, Brian S. (31 January 2022). "The molecular phylogenetic position of Mariplanella piscadera sp. nov. reveals a new major group of rhabdocoel flatworms: Mariplanellida status novus (Platyhelminthes: Rhabdocoela)". Organisms Diversity & Evolution. 22 (3): 577–584. doi:10.1007/s13127-022-00542-2. eISSN   1618-1077. ISSN   1439-6092. S2CID   246467772.
  6. Dumont, Henri; Rietzler, Arnola; Han, Bo-Ping (2014). "A review of typhloplanid flatworm ecology, with emphasis on pelagic species". Inland Waters. 4 (3): 257–270. doi:10.5268/IW-4.3.558. ISSN   2044-2041. S2CID   85379992.
  7. Douglas, Angela E. (2007). "Experimental studies on symbioticChlorellain the Neorhabdocoel Turbellaria Dalyellia viridis and Typhloplana viridata". British Phycological Journal. 22 (2): 157–161. doi:10.1080/00071618700650181. ISSN   0007-1617.
  8. Cristina Damborenea, M.; Cannon, Lester R. G. (2001). "On neotropical Temnocephala (Platyhelminthes)". Journal of Natural History. 35 (8): 1103–1118. doi:10.1080/00222930152434454. ISSN   0022-2933. S2CID   85828730.