Difference between revisions of "Nemertea" - New World Encyclopedia

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| phylum = '''Nemertea'''
 
| phylum = '''Nemertea'''
 
| phylum_authority = [[Max Johann Sigismund Schultze|Schultze]], 1851
 
| phylum_authority = [[Max Johann Sigismund Schultze|Schultze]], 1851
−
| synonyms = Rhyncocoela&nbsp;<ref name="ITIS">{{ITIS|ID=57411|taxon=Nemertea}}</ref>
+
| synonyms = Rhyncocoela
 
| subdivision_ranks = [[Class (biology)|Classes]]
 
| subdivision_ranks = [[Class (biology)|Classes]]
 
| subdivision = [[Anopla]]<br />[[Enopla]]
 
| subdivision = [[Anopla]]<br />[[Enopla]]
 
}}
 
}}
−
'''Nemertea''' is a [[phylum]] of largely aquatic [[invertebrate]] [[animal]]s also known as '''ribbon worms''' or '''proboscis worms''' and characterized by long, thin, unsegmented body that is flattened posteriorly and cylindrical anteriorly and has a long retractable proboscis that can evert for such purposes as capturing prey, defense, and locomotion. Most of the 1,400 or so [[species]] are marine, with a few living in [[freshwater]] and a small number of [[terrestrial animal|terrestrial forms]]. While the smallest reaches only 0.5 centimeters, the largest ones can reach 30 meters long, and reportedly even 50 meters in length, which would make it the world's longest animal.  
+
'''Nemertea''' is a [[phylum]] of largely aquatic [[invertebrate]] [[animal]]s also known as '''ribbon worms''' or '''proboscis worms''' and characterized by long, thin, unsegmented body that is flattened posteriorly and cylindrical anteriorly and has a long retractable proboscis that can evert for such purposes as capturing prey, defense, and locomotion. Most of the 1,400 or so [[species]] are marine, with a few living in [[freshwater]] and a small number of fully [[terrestrial animal|terrestrial forms]]. While the smallest reaches only 0.5 centimeters, the largest ones can reach 30 meters long, and reportedly even 50 meters in length, which would make it the world's longest animal.  
  
 
carnivorous
 
carnivorous
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Nemerteans often have numerous [[gonad]]s, and most species have separate sexes, although all the freshwater forms are [[hermaphrodite|hermaphroditic]]. [[Fertilization]] is usually [[external fertilization|external]], although some species have both [[internal fertilization]] and [[live birth]] (Moore and Gibson 2001).
 
Nemerteans often have numerous [[gonad]]s, and most species have separate sexes, although all the freshwater forms are [[hermaphrodite|hermaphroditic]]. [[Fertilization]] is usually [[external fertilization|external]], although some species have both [[internal fertilization]] and [[live birth]] (Moore and Gibson 2001).
  
−
Nemerteans are found in all marine habits and throughout the world's oceans (Moore and Gibson 2001), as well as in some freshwater habitats, and more rarely terrestrial. They mainly are found in shallow waters, beneath stones, shells, among algae, and burrowing into the substrate (Smith 2008).
+
Some nemerteans, such as the bootlace worm (''Lineus sp.'') have exhibited regeneration, which offers another means of reproduction (Smith 2008).
 +
 
 +
Nemerteans range in size from 5 millimeters (0.2 inches) to over 30 meters (98 feet) long in the case of the European ''[[Lineus longissimus]]''. There are also reports of specimens up to 50 or 60 meters (164-197 feet) long, which would make it the longest animal in the world (Telnes; Smith 2008); the longest vertebrate on record is a female [[Blue Whale|blue whale]], 29.9 meters (98 feet) long.  
  
 
Nemerteans are named for Nemertes, one of the [[Nereids]] of [[Greek mythology]], and alternative spellings for the phylum have included '''Nemertini''' and '''Nemertinea'''.
 
Nemerteans are named for Nemertes, one of the [[Nereids]] of [[Greek mythology]], and alternative spellings for the phylum have included '''Nemertini''' and '''Nemertinea'''.
−
 
−
===Length===
 
−
Nemerteans range in size from 5&nbsp;[[millimetre|mm]] to over 30&nbsp;[[metre]]s long in the case of the European ''[[Lineus longissimus]]''. There are also reports of specimens up to 50&nbsp;m or 60&nbsp;m long, which would make it the longest animal in the world&nbsp;<ref>{{cite web |url=http://www.seawater.no/fauna/slimormer/kjempe.htm |title=Giant ribbon worm |publisher=The Marine Fauna Gallery of Norway |accessdate=2007-08-10 |author=Kåre Telnes}}</ref>; the longest vertebrate on record is a female [[Blue Whale|blue whale]], 29.9&nbsp;m long&nbsp;<ref>{{cite web  |url=http://www.wildwhales.org/cetaceans/blue/sr_blue_whale_e.pdf.pdf |title=COSEWIC Assessment and Update Status Report on the  Blue Whale ''Balaenoptera musculus'' in Canada |publisher=Committee on the Status of Endangered Wildlife in Canada. Ottawa |year=2002}}</ref>.
 
−
 
−
Nemerteans are arranged into two classes, the Anopla and Enopla.
 
−
 
−
 
−
 
−
&nbsp;<ref name="Moore">{{cite book |author=J. Moore & R. Gibson |title=Nemertea |publisher=[[Encyclopedia of Life Sciences]] |doi=10.1038/npg.els.0001586 |year=2001 |pages=4 pp}}</ref>.
 
  
 
==Ecology and distribution==
 
==Ecology and distribution==
−
The majority of nemertean worms live on or in the sea floor, with many species extending into [[brackish water]] in estuaries, and some [[fresh water|freshwater]] or fully [[terrestrial animal|terrestrial]] species. Freshwater genera include the large genus ''[[Prostoma]]'', while the terrestrial forms are best represented by ''[[Geonemertes]]'', a genus mostly found in [[Australasia]], but with one species in the [[Seychelles]], one found widely across the [[Indo-Pacific]], one from [[Tristan da Cunha]] in the South Atlantic, and one, ''G. chalicophora'', first found in the ''[[Palmengarten]]'' in [[Frankfurt]], but since discovered in the [[Canary Islands]], [[Madeira]] and the [[Azores]]&nbsp;<ref name="Gibson"/>.
+
The majority of nemertean worms live on or in the sea floor, with many species extending into [[brackish water]] in estuaries, and some [[fresh water|freshwater]] or fully [[terrestrial animal|terrestrial]] species. Freshwater genera include the large genus ''[[Prostoma]]'', while the terrestrial forms are best represented by ''[[Geonemertes]]'', a genus mostly found in [[Australasia]], but with one species in the [[Seychelles]], one found widely across the [[Indo-Pacific]], one from [[Tristan da Cunha]] in the South Atlantic, and one, ''G. chalicophora'', first found in the ''[[Palmengarten]]'' in [[Frankfurt]], but since discovered in the [[Canary Islands]], [[Madeira]], and the [[Azores]] (Gibson 1995).
  
−
They are often found in and among [[seaweed]]s, [[Rock (geology)|rock]]s, [[mussel]] and [[barnacle]] beds, or buried in mud, sand, or gravel substrates.
+
Nemerteans are found in all marine habits and throughout the world's oceans (Moore and Gibson 2001). They are often found in shallow waters, in and among [[seaweed]]s, [[Rock (geology)|rock]]s, [[mussel]] and [[barnacle]] beds, or buried in mud, sand, or gravel substrates.  
  
−
Most nemerteans are carnivorous and [[predator]]y, catching prey with their [[proboscis]]&nbsp;<ref name="bee">{{cite web |url=http://www.bumblebee.org/invertebrates/NEMERTEA.htm |title=Nemertea (ribbon worms) |publisher=[[bumblebee.org]] |accessdate=2007-08-10}}</ref>, although some are [[scavenger]]s and some are [[herbivore]]s&nbsp;<ref>{{cite web |url=http://www.seamuse.com/rhyncocoela.htm |title=Phylum Rhyncocoela |author=Stephen Shaner |publisher=Seamuse.org |accessdate=2007-08-10}}</ref>. In some families, it is armed with a sharp stylet which may be poisonous, while those that lack the stylet often use a sticky secretion on the proboscis to entrap their prey. The proboscis is wrapped around the prey, which is normally other invertebrates such as [[crustacean]]s and [[annelid]]s and can be many times larger than the nemertean itself, and the prey is then stabbed repeatedly with the stylet until dead&nbsp;<ref name="Waggoner"/>. A few, such as ''[[Malacobdella]]'', live parasitically in the [[mantle (mollusc)|mantle cavity]] of [[mollusc]]s and live on the food filtered by their hosts&nbsp;<ref name="Waggoner"/>.
+
Most nemerteans are carnivorous and [[predator]]y, catching prey with their [[proboscis]] (Smith 2008). However, some are [[scavenger]]s and some are [[herbivore]]s (Shaner). A few, such as ''[[Malacobdella]]'', live parasitically in the [[mantle (mollusc)|mantle cavity]] of [[mollusk]]s and live on the food filtered by their hosts (Waggoner and Collins 2001).
  
 +
Carnivorous nemerteans normally prey upon other invertebrates, such as [[crustacean]]s and [[annelid]]s, and these can be many times larger than the nemertean itself. In some families, the nemertean is armed with a sharp stylet, which may be poisonous. The proboscis is wrapped around the prey and the prey is then stabbed repeatedly with the stylet until dead (Waggoner and Collins 2001). Those that lack the stylet often use a sticky secretion on the proboscis to entrap their prey.
  
 +
==Classification==
 +
The earliest record of a nemertean worm is probably an account by [[Olaus Magnus]] in 1555 of a long, greyish-blue marine worm, which is probably ''[[Lineus longissimus]]'', but the first species was not formally described until [[Johan Ernst Gunnerus|Gunnerus]] described the same species (as ''Ascaris longissima'') in 1770&nbsp;<ref name="Gibson">{{cite journal |quotes=no |author=R. Gibson |year=1995 |title=Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution |journal=[[Journal of Natural History]] |volume=29 |issue=2 |pages=271–561 |doi=10.1080/00222939500770161}}</ref>. In 1995, a total of 1,149 species had been described, and grouped into 250 genera&nbsp;<ref name="Gibson"/>. Nemerteans are arranged into two classes, the Anopla and Enopla.
  
−
==Classification==
+
Phylum Rhyncocoela
−
The earliest record of a nemertean worm is probably an account by [[Olaus Magnus]] in 1555 of a long, greyish-blue marine worm, which is probably ''[[Lineus longissimus]]'', but the first species was not formally described until [[Johan Ernst Gunnerus|Gunnerus]] described the same species (as ''Ascaris longissima'') in 1770&nbsp;<ref name="Gibson">{{cite journal |quotes=no |author=R. Gibson |year=1995 |title=Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution |journal=[[Journal of Natural History]] |volume=29 |issue=2 |pages=271–561 |doi=10.1080/00222939500770161}}</ref>. In 1995, a total of 1,149 species had been described, and grouped into 250 genera&nbsp;<ref name="Gibson"/>.
 
  
 
The [[fossil record]] of the phylum is sparse, as expected for a group of soft-bodied animals, but even the hard stylets are not found. The only possible nemertean fossil is ''[[Archisymplectes]]'' from the [[Mazon Creek]] biota of the [[Pennsylvanian]] of [[Illinois]]&nbsp;<ref name="Waggoner">{{cite web |url=http://www.ucmp.berkeley.edu/nemertini/nemertini.html |title=Introduction to the Nemertini |publisher=[[University of California, Berkeley]] |date=2001-06-13 |author=Ben Waggoner & Allen G. Collins}}</ref>.
 
The [[fossil record]] of the phylum is sparse, as expected for a group of soft-bodied animals, but even the hard stylets are not found. The only possible nemertean fossil is ''[[Archisymplectes]]'' from the [[Mazon Creek]] biota of the [[Pennsylvanian]] of [[Illinois]]&nbsp;<ref name="Waggoner">{{cite web |url=http://www.ucmp.berkeley.edu/nemertini/nemertini.html |title=Introduction to the Nemertini |publisher=[[University of California, Berkeley]] |date=2001-06-13 |author=Ben Waggoner & Allen G. Collins}}</ref>.
Line 60: Line 55:
  
 
* Integrated Taxonomic Information System (ITIS). 1999. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=57411 Nemertea] ''ITIS Taxonomic Serial No.: 57411''. Retrieved December 20, 2008.
 
* Integrated Taxonomic Information System (ITIS). 1999. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=57411 Nemertea] ''ITIS Taxonomic Serial No.: 57411''. Retrieved December 20, 2008.
 +
 +
R. Gibson (1995). "Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution". Journal of Natural History 29 (2): 271–561. doi:10.1080/00222939500770161
 +
 +
&nbsp;<ref name="Moore">{{cite book |author=J. Moore & R. Gibson |title=Nemertea |publisher=[[Encyclopedia of Life Sciences]] |doi=10.1038/npg.els.0001586 |year=2001 |pages=4 pp}}</ref>.
  
 
L. Smith 2008
 
L. Smith 2008
 
http://www.bumblebee.org/invertebrates/NEMERTEA.htm Nemertea (ribbon worms, proboscis worms)  
 
http://www.bumblebee.org/invertebrates/NEMERTEA.htm Nemertea (ribbon worms, proboscis worms)  
 
Bumblebee.org
 
Bumblebee.org
 +
 +
&nbsp;<ref name="bee">{{cite web |url=http://www.bumblebee.org/invertebrates/NEMERTEA.htm |title=Nemertea (ribbon worms) |publisher=[[bumblebee.org]] |accessdate=2007-08-10}}</ref>,
  
 
&nbsp;<ref>{{cite journal |quotes=no |journal=[[Molecular Biology and Evolution]] |volume=9 |issue=2 |pages=235–249 |year=1992 |title=Phylogenetic position of Phylum Nemertini, inferred from 18s rRNA sequences: molecular data as a test of morphological character homology |author=J. McClintock Turbeville, K. G. Field & R. A. Rafl}}</ref>.  
 
&nbsp;<ref>{{cite journal |quotes=no |journal=[[Molecular Biology and Evolution]] |volume=9 |issue=2 |pages=235–249 |year=1992 |title=Phylogenetic position of Phylum Nemertini, inferred from 18s rRNA sequences: molecular data as a test of morphological character homology |author=J. McClintock Turbeville, K. G. Field & R. A. Rafl}}</ref>.  
 +
 +
 +
&nbsp;<ref>{{cite web |url=http://www.seamuse.com/rhyncocoela.htm |title=Phylum Rhyncocoela |author=Stephen Shaner |publisher=Seamuse.org |accessdate=2007-08-10}}</ref>.
 +
 +
&nbsp;<ref>{{cite web |url=http://www.seawater.no/fauna/slimormer/kjempe.htm |title=Giant ribbon worm |publisher=The Marine Fauna Gallery of Norway |accessdate=2007-08-10 |author=Kåre Telnes}}</ref>
 +
 +
Ben Waggoner & Allen G. Collins (2001-06-13). "Introduction to the Nemertini". University of California, Berkeley.
  
 
[[Category:Life sciences]]
 
[[Category:Life sciences]]

Revision as of 22:33, 20 December 2008

Nemertea
Parborlasia corrugatus from the Ross Sea
Parborlasia corrugatus from the Ross Sea
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
Superphylum: Lophotrochozoa
Phylum: Nemertea
Schultze, 1851
Classes

Anopla
Enopla

Synonyms

Rhyncocoela

Nemertea is a phylum of largely aquatic invertebrate animals also known as ribbon worms or proboscis worms and characterized by long, thin, unsegmented body that is flattened posteriorly and cylindrical anteriorly and has a long retractable proboscis that can evert for such purposes as capturing prey, defense, and locomotion. Most of the 1,400 or so species are marine, with a few living in freshwater and a small number of fully terrestrial forms. While the smallest reaches only 0.5 centimeters, the largest ones can reach 30 meters long, and reportedly even 50 meters in length, which would make it the world's longest animal.

carnivorous

Description

Nemertean worms are soft-bodied, unsegmented animals, typically with an elongate body that is long and thin, and distinguished by the presence of an eversible proboscis. The anterior portion of the body is cyclindrical and the posterior part is flattened (Smith 2008). Although generally considered acoelomate, the cavity which contains the proboscis includes a true coelom (Turbeville et al. 1992). The circulatory system of nemerteans is closed, as is the digestive system, which includes a separate mouth and anus (unlike flatworms, which have a single opening). The mouth is ventral. Body movements and contractions of the blood vessel walls drives the blood flow system (Smith 2008). The nervous system includes a brain and several nerve cords; nemerteans also have pigment-cup eyes, ranging from two to 250 such eyes depending on the species (Smith 2008). respiration is entirely by diffusion (Smith 2008).

Nemertean worms are unique in possessing a "cerebral organ"—a sensory and regulatory organ closely associated with the brain (Moore and Gibson 2001).

The proboscis, when retracted, sits in a dorsal cavity, separate from the digestive tract, that takes up most of the length of the worm. Muscular contraction causes pressure in the proboscis cavity and everts the proboscis. The action of a longitudinal muscle causes retraction. The proboscis serves for capturing prey, and can also be used in locomotion and defense (Smith 2008).

Nemerteans often have numerous gonads, and most species have separate sexes, although all the freshwater forms are hermaphroditic. Fertilization is usually external, although some species have both internal fertilization and live birth (Moore and Gibson 2001).

Some nemerteans, such as the bootlace worm (Lineus sp.) have exhibited regeneration, which offers another means of reproduction (Smith 2008).

Nemerteans range in size from 5 millimeters (0.2 inches) to over 30 meters (98 feet) long in the case of the European Lineus longissimus. There are also reports of specimens up to 50 or 60 meters (164-197 feet) long, which would make it the longest animal in the world (Telnes; Smith 2008); the longest vertebrate on record is a female blue whale, 29.9 meters (98 feet) long.

Nemerteans are named for Nemertes, one of the Nereids of Greek mythology, and alternative spellings for the phylum have included Nemertini and Nemertinea.

Ecology and distribution

The majority of nemertean worms live on or in the sea floor, with many species extending into brackish water in estuaries, and some freshwater or fully terrestrial species. Freshwater genera include the large genus Prostoma, while the terrestrial forms are best represented by Geonemertes, a genus mostly found in Australasia, but with one species in the Seychelles, one found widely across the Indo-Pacific, one from Tristan da Cunha in the South Atlantic, and one, G. chalicophora, first found in the Palmengarten in Frankfurt, but since discovered in the Canary Islands, Madeira, and the Azores (Gibson 1995).

Nemerteans are found in all marine habits and throughout the world's oceans (Moore and Gibson 2001). They are often found in shallow waters, in and among seaweeds, rocks, mussel and barnacle beds, or buried in mud, sand, or gravel substrates.

Most nemerteans are carnivorous and predatory, catching prey with their proboscis (Smith 2008). However, some are scavengers and some are herbivores (Shaner). A few, such as Malacobdella, live parasitically in the mantle cavity of mollusks and live on the food filtered by their hosts (Waggoner and Collins 2001).

Carnivorous nemerteans normally prey upon other invertebrates, such as crustaceans and annelids, and these can be many times larger than the nemertean itself. In some families, the nemertean is armed with a sharp stylet, which may be poisonous. The proboscis is wrapped around the prey and the prey is then stabbed repeatedly with the stylet until dead (Waggoner and Collins 2001). Those that lack the stylet often use a sticky secretion on the proboscis to entrap their prey.

Classification

The earliest record of a nemertean worm is probably an account by Olaus Magnus in 1555 of a long, greyish-blue marine worm, which is probably Lineus longissimus, but the first species was not formally described until Gunnerus described the same species (as Ascaris longissima) in 1770 [1]. In 1995, a total of 1,149 species had been described, and grouped into 250 genera [1]. Nemerteans are arranged into two classes, the Anopla and Enopla.

Phylum Rhyncocoela

The fossil record of the phylum is sparse, as expected for a group of soft-bodied animals, but even the hard stylets are not found. The only possible nemertean fossil is Archisymplectes from the Mazon Creek biota of the Pennsylvanian of Illinois [2].

Once classified as "degenerate" flatworms, nemerteans are now recognised as a separate phylum, more closely related to higher, coelomate phyla in Lophotrochozoa, such as Annelida and Mollusca [3].

The traditional classes of Enopla for nemerteans armed with one or more stylets and Anopla for those without are not monophyletic is not supported by molecular data [4]. Similarly, the subclass Bdellonemertea, erected for nemerteans which live as parasites on molluscs, is nested within Hoplonemertea, and probably represents a specislised offshoot from that group rather than an independent lineage [4]. Recent molecular phylogenetic study has, however, confirmed the monophyly of each of Heteronemertea and Hoplonemertea, as well as the expected paraphyly of Palaeonemertea [5].

References
ISBN links support NWE through referral fees

  1. ↑ 1.0 1.1 R. Gibson (1995). Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution. Journal of Natural History 29 (2): 271–561.
  2. ↑ Ben Waggoner & Allen G. Collins (2001-06-13). Introduction to the Nemertini. University of California, Berkeley.
  3. ↑ Bilateria. Tree of Life Web Project (2002-01-01).
  4. ↑ 4.0 4.1 Per Sundberg, J. M. Turbeville and Susanne Lindh (2001). Phylogenetic relationships among higher nemertean (Nemertea) taxa inferred from 18S rDNA sequences. Molecular Phylogenetics and Evolution 20 (3): 327–334.
  5. ↑ Mikael Thollesson and Jon L. Norenburg (2003). Ribbon worm relationships: a phylogeny of the phylum Nemertea. Proceedings of the Royal Society of London B 270: 407–415.
  • Integrated Taxonomic Information System (ITIS). 1999. Nemertea ITIS Taxonomic Serial No.: 57411. Retrieved December 20, 2008.

R. Gibson (1995). "Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution". Journal of Natural History 29 (2): 271–561. doi:10.1080/00222939500770161

 [1].

L. Smith 2008 http://www.bumblebee.org/invertebrates/NEMERTEA.htm Nemertea (ribbon worms, proboscis worms) Bumblebee.org

 [2],

 [3]. 


 [4].

 [5]

Ben Waggoner & Allen G. Collins (2001-06-13). "Introduction to the Nemertini". University of California, Berkeley.

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  1. ↑ J. Moore & R. Gibson (2001). Nemertea. Encyclopedia of Life Sciences, 4 pp. DOI:10.1038/npg.els.0001586. 
  2. ↑ Nemertea (ribbon worms). bumblebee.org. Retrieved 2007-08-10.
  3. ↑ J. McClintock Turbeville, K. G. Field & R. A. Rafl (1992). Phylogenetic position of Phylum Nemertini, inferred from 18s rRNA sequences: molecular data as a test of morphological character homology. Molecular Biology and Evolution 9 (2): 235–249.
  4. ↑ Stephen Shaner. Phylum Rhyncocoela. Seamuse.org. Retrieved 2007-08-10.
  5. ↑ Kåre Telnes. Giant ribbon worm. The Marine Fauna Gallery of Norway. Retrieved 2007-08-10.
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