Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956.[1]
Most gnathostomulids measure 0.5 to 1 millimetre (0.02 to 0.04 in) in length. They are often slender to thread-like worms, with a generally transparent body. In many Bursovaginoidea, one of the major group of gnathostomulids, the neck region is slightly narrower than the rest of the body, giving them a distinct head.[2]
Like flatworms they have a ciliatedepidermis, but in contrast to flatworms, they have one cilium per cell.[3] The cilia allow the worms to glide along in the water between sand grains, although they also use muscles, allowing the body to twist or contract, for movement.
They have no body cavity, and no circulatory or respiratory system. The nervous system is simple, and restricted to the outer layers of the body wall. The only sense organs are modified cilia, which are especially common in the head region.[2]
The mouth is located just behind the head, after a rostrum, on the underside of the body. It has a pair of cuticular jaws, supplied by strong muscles, and often bearing minute teeth. A "basal plate" on the lower surface that bears a comb-like structure is also present. The basal plate is used to scrape smaller organisms off of the grains of sand that make up their anoxic seabed mud habitat.[4] This bilaterally symmetrical pharynx with its complex cuticular mouth parts make them appear closely related to rotifers and their allies, together making up the Gnathifera. The ultrastructure of the jaws made of rods with electron dense core in transmission electron microscopy sections also support their close relation with Rotifera and Micrognathozoa. The mouth opens into a blind-ending tube in which digestion takes place; there is no true anus.[2] However, there is tissue connecting the intestine to the epidermis which may serve as an anal pore.[5]
Reproductionedit
Gnathostomulids are simultaneous hermaphrodites. Each individual possesses a single ovary and one or two testes. After fertilization, the single egg ruptures through the body wall and adheres to nearby sand particles; the parent is able to rapidly heal the resulting wound. The egg hatches into a miniature version of the adult, without a larval stage.[2]
There are approximately 100 described species[6] and certainly many more as yet undescribed. The known species are grouped in two orders. The filospermoids are very long and are characterized by an elongate rostrum. The bursovaginoids have paired sensory organs and are characterized by the presence of a penis and a sperm-storage organ called a bursa.[4]
Gnathostomulids have no known fossil record, though there are (debatable) similarities between the jaws of modern gnathostomulids and certain conodont elements. (Ochietti & Cailleux, 1969; Durden et al, 1969)[7]
Wikimedia Commons has media related to Gnathostomulida.
Wikispecies has information related to Gnathostomulida.
^ abAx, P. (1956). "Die Gnathostomulida, eine rätselhafte Wurmgruppe aus dem Meeressand". Abhandl. Akad. Wiss. U. Lit. Mainz, Math. - Naturwiss. 8: 1–32.
^ abcdeBarnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 311–312. ISBN0-03-056747-5.
^Ruppert, Edward E., Fox, Richard S., Barnes, Robert D. (2004) Invertebrate Zoology (7th edition). Brooks/Cole-Thomson Learning, Belmont, US
^ abBarnes, R.F.K. et al. (2001). The Invertebrates: A Synthesis. Oxford: Blackwell Science.
^Knauss, Elizabeth (December 1979). "Indication of an Anal Pore in Gnathostomulida". Zoologica Scripta. 8 (1–4): 181–6. doi:10.1111/j.1463-6409.1979.tb00630.x.
^Zhang, Z.-Q. (2011). "Animal biodiversity: An introduction to higher-level classification and taxonomic richness" (PDF). Zootaxa. 3148: 7–12. doi:10.11646/zootaxa.3148.1.3. Archived (PDF) from the original on 2022-10-09.
^Cited in chapter 2 , p192 of Andreas Schmidt-Rhaesa'a 2015 Gastrotricha and Gnathifera, VOl 3 of Gast---, Cycloneuralia and Gnath---.
^Golombek, A.; Tobergte, S.; Struck, T.H. (May 2015). "Elucidating the phylogenetic position of Gnathostomulida and first mitochondrial genomes of Gnathostomulida, Gastrotricha and Polycladida (Platyhelminthes)". Mol Phylogenet Evol. 86: 49–63. doi:10.1016/j.ympev.2015.02.013. PMID 25796325.
gnathostomulid, worms, small, phylum, nearly, microscopic, marine, animals, they, inhabit, sand, beneath, shallow, coastal, waters, survive, relatively, anoxic, environments, they, were, first, recognised, described, 1956, wormsgnathostomula, paradoxascientifi. Gnathostomulids or jaw worms are a small phylum of nearly microscopic marine animals They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments They were first recognised and described in 1956 1 Jaw wormsGnathostomula paradoxaScientific classificationDomain EukaryotaKingdom AnimaliaSubkingdom EumetazoaClade ParaHoxozoaClade BilateriaClade Nephrozoa unranked Protostomia unranked SpiraliaClade GnathiferaPhylum GnathostomulidaAx 1956 1 Orders and subordersFilospermoidea Bursovaginoidea Conophoralia Scleroperalia Contents 1 Anatomy 2 Reproduction 3 Taxonomy 4 ReferencesAnatomy editMost gnathostomulids measure 0 5 to 1 millimetre 0 02 to 0 04 in in length They are often slender to thread like worms with a generally transparent body In many Bursovaginoidea one of the major group of gnathostomulids the neck region is slightly narrower than the rest of the body giving them a distinct head 2 Like flatworms they have a ciliated epidermis but in contrast to flatworms they have one cilium per cell 3 The cilia allow the worms to glide along in the water between sand grains although they also use muscles allowing the body to twist or contract for movement They have no body cavity and no circulatory or respiratory system The nervous system is simple and restricted to the outer layers of the body wall The only sense organs are modified cilia which are especially common in the head region 2 The mouth is located just behind the head after a rostrum on the underside of the body It has a pair of cuticular jaws supplied by strong muscles and often bearing minute teeth A basal plate on the lower surface that bears a comb like structure is also present The basal plate is used to scrape smaller organisms off of the grains of sand that make up their anoxic seabed mud habitat 4 This bilaterally symmetrical pharynx with its complex cuticular mouth parts make them appear closely related to rotifers and their allies together making up the Gnathifera The ultrastructure of the jaws made of rods with electron dense core in transmission electron microscopy sections also support their close relation with Rotifera and Micrognathozoa The mouth opens into a blind ending tube in which digestion takes place there is no true anus 2 However there is tissue connecting the intestine to the epidermis which may serve as an anal pore 5 Reproduction editGnathostomulids are simultaneous hermaphrodites Each individual possesses a single ovary and one or two testes After fertilization the single egg ruptures through the body wall and adheres to nearby sand particles the parent is able to rapidly heal the resulting wound The egg hatches into a miniature version of the adult without a larval stage 2 Taxonomy editSee also List of bilaterial animal orders There are approximately 100 described species 6 and certainly many more as yet undescribed The known species are grouped in two orders The filospermoids are very long and are characterized by an elongate rostrum The bursovaginoids have paired sensory organs and are characterized by the presence of a penis and a sperm storage organ called a bursa 4 Gnathostomulids have no known fossil record though there are debatable similarities between the jaws of modern gnathostomulids and certain conodont elements Ochietti amp Cailleux 1969 Durden et al 1969 7 They appear to be a sister clade to the Syndermata 2 8 References edit nbsp Wikimedia Commons has media related to Gnathostomulida nbsp Wikispecies has information related to Gnathostomulida a b Ax P 1956 Die Gnathostomulida eine ratselhafte Wurmgruppe aus dem Meeressand Abhandl Akad Wiss U Lit Mainz Math Naturwiss 8 1 32 a b c d e Barnes Robert D 1982 Invertebrate Zoology Philadelphia PA Holt Saunders International pp 311 312 ISBN 0 03 056747 5 Ruppert Edward E Fox Richard S Barnes Robert D 2004 Invertebrate Zoology 7th edition Brooks Cole Thomson Learning Belmont US a b Barnes R F K et al 2001 The Invertebrates A Synthesis Oxford Blackwell Science Knauss Elizabeth December 1979 Indication of an Anal Pore in Gnathostomulida Zoologica Scripta 8 1 4 181 6 doi 10 1111 j 1463 6409 1979 tb00630 x Zhang Z Q 2011 Animal biodiversity An introduction to higher level classification and taxonomic richness PDF Zootaxa 3148 7 12 doi 10 11646 zootaxa 3148 1 3 Archived PDF from the original on 2022 10 09 Cited in chapter 2 p192 of Andreas Schmidt Rhaesa a 2015 Gastrotricha and Gnathifera VOl 3 of Gast Cycloneuralia and Gnath Golombek A Tobergte S Struck T H May 2015 Elucidating the phylogenetic position of Gnathostomulida and first mitochondrial genomes of Gnathostomulida Gastrotricha and Polycladida Platyhelminthes Mol Phylogenet Evol 86 49 63 doi 10 1016 j ympev 2015 02 013 PMID 25796325 Gnatostomulida Integrated Taxonomic Information System Retrieved from https en wikipedia org w index php title Gnathostomulid amp oldid 1194569271, wikipedia, wiki, book, books, library,
