Phoronid
Phoronids Temporal range:
| |
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Phoronis sp. | |
Phoronopsis harmeri | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
(unranked): | Spiralia |
Superphylum: | Lophotrochozoa |
Clade: | Lophophorata |
Clade: | Brachiozoa |
Phylum: | Phoronida Hatschek, 1888 |
Genera | |
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Phoronids (scientific name Phoronida, sometimes called horseshoe worms) are a small
The name of the group comes from its type genus: Phoronis.[2][3]
Overview
The bottom end of the body is an ampulla (a flask-like swelling), which anchors the animal in the tube and enables it to retract its body very quickly when threatened. When the lophophore is extended at the top of the body,
A blood vessel leads up the middle of the body from the stomach to a circular vessel at the base of the lophophore, and from there a single blind vessel runs up each tentacle. A pair of blood vessels near the body wall lead downward from the lophophore ring to the stomach and also to blind branches throughout the body. There is no heart, but the major vessels can contract in waves to move the blood. Phoronids do not ventilate their trunks with oxygenated water, but rely on
One species builds colonies by budding or by splitting into top and bottom sections, and all phoronids reproduce sexually from spring to autumn. The eggs of most species form free-swimming actinotroch larvae, which feed on plankton. An actinotroch settles to the seabed after about 20 days and then undergoes a radical change in 30 minutes: the larval tentacles are replaced by the adult lophophore; the anus moves from the bottom to just outside the lophophore; and this changes the gut from upright to a U-bend, with the stomach at the bottom of the body. One species forms a "slug-like" larva, and the larvae of a few species are not known. Phoronids live for about one year.
Some species live separately, in vertical tubes embedded in soft
As of 2010 there are no indisputable body fossils of phoronids.
Comparison of similar phyla
Feature | Phoronids[8] | Brachiopods[9] | Bryozoans[10] | Entoprocts[11]
|
---|---|---|---|---|
Tentacles hollow | Yes | Yes | Yes | No |
Protection and support | Erect tube of chitin | Shell with two valves | Various, including chitin, mineralized skeletons, plant-like shapes, and a mass of gelatinous material | None |
Feeding flow | Top to bottom | In through sides of shell, out through front | Top to bottom | Bottom to top |
Anus | Outside ring of tentacles | In the mantle, or none and solid waste is ejected out of the mouth[12] |
Outside ring of tentacles | Inside ring of tentacles |
Colonial | One species | No | All but one genus | Most species colonial |
Coelom | Yes | Yes | Yes | No |
Description
Body structure
Most adult phoronids are 2 to 20 cm long and about 1.5 mm wide,
For feeding and
The mouth is inside the base of the crown of tentacles but to one side. The gut runs from the mouth to one side of the stomach, in the bottom of the ampulla. The intestine runs from the stomach, up the other side of the body, and exits at the anus, outside and a little below the crown of tentacles. The gut and intestine are both supported by two mesenteries (partitions that run the length of the body) connected to the body wall, and another mesentery connects the gut to the intestine.[8]
The body is divided into coeloms,[8] compartments lined with mesothelium.[17] The main body cavity, under the crown of tentacles, is called the metacoelom, and the tentacles and their base share the mesocoelom.[8] Above the mouth is the epistome, a hollow lid which can close the mouth.[13] The cavity in the epistome is sometimes called the protocoelom, although other authors disagree that it is a coelom[18] and Ruppert, Fox and Barnes think it is built by a different process.[8]
The tube comprises a three-layered organic inner cylinder, and an agglutinated external layer.[19]
Feeding, circulation and excretion
When the lophophore is extended,
A blood vessel
Nervous system and movement
There is a nervous center between the mouth and anus, and a nerve ring at the base of the lophophore.[1] The ring supplies nerves to the tentacles and, just under the skin, to the body-wall muscles. Phoronis ovalis has two nerve trunks under the skin, whereas other species have one.[8] The trunk(s) have giant axons (nerves that transmit signals very fast) which co-ordinate the retraction of the body when danger threatens.[13]
Except for retracting the body into the tube, phoronids have limited and slow movement: partial emerging from the tube; bending the body when extended; and the lophophore's flicking of food into the mouth.[8]
Reproduction and lifecycle
Only the smallest species of horseshoe worms,
Development of the eggs is a mixture of deuterostome and protostome characteristics. Early divisions of the egg are holoblastic (the cells divide completely) and radial (they gradually form a stack of circles). The process is regulative (the fate of each cell depends on interaction with other cells, not on a rigid program in each cell), and experiments that divided early embryos produced complete larvae. Mesoderm is formed from mesenchyme originating from the archenteron. The coelom is formed by
The slug-like larva of Phoronis ovalis, the only known species with a lecithotrophic (non-feeding) larvae, lack tentacles and swims for about 4 days, creeps on the seabed for 3 to 4 days, then bores into a carbonate floor.
Phoronids live for about one year.[1]
Ecology
Phoronids live in all the oceans and seas including the
Although predators of phoronids are not well known, they include fish,
It is unknown whether phoronids have any significance for humans. The
Evolutionary history
Fossil record
As of 2016 there are no indisputable body fossils of phoronids.
There is good evidence that species of Phoronis created the
Family tree
Phoronids,
Nielsen (2002) views the phoronids and brachiopods as affiliated with the deuterostome
- While deuterostomes have three coelomic cavities, lophophorates such as phoronids and brachiopods have only two.[18]
- Pterobranchs may be a sub-group of synapomorphy of lophophorates and deuterostomes, but evolved independently as convergent adaptations to a sessile lifestyle.[6][48][49]
- The mesoderm does not form by enterocoely in phoronids and bryozoans, but does in deuterostomes, while there are disagreements about whether brachiopods form the mesoderm by enterocoely.[6]
Protostomia
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From 1988 onwards analyses based on
While analyses by molecular phylogeny are confident that members of Lophotrochozoa are more closely related to each other than of non-members, the relationships between members are mostly unclear.
Molecular phylogeny indicates that Phoronida are closely related to Brachiopoda, but
Taxonomy
Adult species[1] | Larva species[1] |
---|---|
Phoronis ovalis | (creeping larva) |
Phoronis hippocrepia | Actinotrocha hippocrepia[30] |
Phoronis ijimai, also called Phoronis vancouverensis |
Actinotrocha vancouverensis |
Phoronis australis | (unknown) |
Phoronis muelleri | Actinotrocha branchiata |
Phoronis psammophila | Actinotrocha sabatieri |
Phoronis pallida | Actinotrocha pallida |
Phoronopsis albomaculata | (unknown) |
Phoronopsis harmeri | Actinotrocha harmeri |
Phoronopsis californica | (unknown) |
The phylum has two
In 1999 Temereva and Malakhov described Phoronis svetlanae.[59] In 2000 Temereva described a new species, Phoronopsis malakhovi,[60] while Emig regards it as a synonym for Phoronopsis harmeri.[1] Santagata thinks Phoronis architecta is a different species from both Phoronis psammophila and Phoronis muelleri, and that "[the phoronids'] species diversity is currently underestimated".[61] In 2009 Temereva described what may be larvae of Phoronopsis albomaculata and Phoronopsis californica. She wrote that, while there are 12 undisputed adult phoronid species, 25 morphological types of larvae have been identified.[34]
Notes
References
- ^ ISBN 978-0-7876-5362-0. Archived from the original(PDF) on 2010-03-27. Retrieved 2011-03-01.
- ^ "Phoronida". Merriam-Webster.com Dictionary. "New Latin, from Phoronis + -ida."
- Argoswho was loved by Zeus)."
- ^ Coral Reefs of the Gulf: Adaptation to Climatic Extremes
- ^ a b Taylor, Paul D.; Olev Vinn; Mark A. Wilson (2010). "Evolution of biomineralization in 'Lophophorates'". Special Papers in Palaeontology. 84: 317–333.
- ^ PMID 18495619.
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- ^ ISBN 978-0-03-025982-1.)
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- ^ "The Structures of Life". National Institute of General Medical Sciences. Archived from the original on 2014-06-07. Retrieved 2011-03-03.
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: CS1 maint: multiple names: authors list (link - ^ "Gonad – Definition". The Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 2011-03-03.
- ISBN 978-90-481-2766-5. Retrieved 2011-03-29.
- ^ "Hermaphrodite – Definition". The Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 2011-03-03.
- ^ "Cross-fertilization – Definition". Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 2011-03-10.
- ^ "Dioecious – Definition". The Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 2011-03-03.
- ^ "Gamete – Definition". The Free Merriam-Webster Dictionary. Merriam-Webster, Incorporated. Retrieved 2011-03-03.
- ^ Bailey-Brock, Julie H.; Christian C. Emig (2000). "Hawaiian Phoronida (Lophophorata) and Their Distribution in the Pacific Region" (PDF). Pacific Science. 54 (2): 119–126. Retrieved 2011-03-11.
- ^ ISBN 978-0-12-026119-2. Retrieved 2011-03-12.
- ^ Development, organization, and remodeling of phoronid muscles from embryo to metamorphosis (Lophotrochozoa: Phoronida)
- ^ Metamorphic remodeling of morphology and the body cavity in Phoronopsis harmeri (Lophotrochozoa, Phoronida): the evolution of the phoronid body plan and life cycle
- PMID 11103334.
- ^ . Retrieved 2011-03-11.
- ^ Stampar, Sergio; Christian C. Emig; Andre C. Morandini; Guilherme Kodja; Ana Paula Balboni; Fabio Lang Da Silveira (2010). "Is there any danger in a symbiotic species associated with an endangered one? A case of a phoronid worm growing on a Ceriantheomorphe tube" (PDF). Cah. Biol. Mar. 51: 205–211. Archived from the original (PDF) on 2010-11-12. Retrieved 2011-03-02.
- ISSN 0171-8630.
- ^ a b Taylor, P.D.; Wilson, M.A (2008). "Morphology and affinities of hederelloid "bryozoans"" (PDF). In Hageman, S.J.; Key, M.M. Jr.; Winston, J.E. (eds.). Bryozoan Studies 2007: Proceedings of the 14th International Bryozoology Conference. Virginia Museum of Natural History. pp. 301–309. Archived from the original (PDF) on 2010-03-26. Retrieved 2011-03-26.
- ^ Chen, J.Y.; G. Zhou. "Biology of the Chengjiang fauna". Bulletin of the National Museum of Natural Science, Taipei. 10: 11–105. – cited by Emig (Mar 2010) and Taylor, Vinn and Wilson(2010)
- ^ Chen, J.Y. (2004). The dawn of the animal world (in Chinese). Nanjing: Jiangsu Science and Technology Press. p. 366. – cited in Taylor, Vinn & Wilson (2010)
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- ^ "Introduction to the Deuterostomia". University of California Museum of Paleontology. Retrieved 2010-03-08.
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- ^ Giribet, Gonzalo; Edgecombe, Gregory (3 March 2020). The Invertebrate Tree of Life. Princeton University Press.
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- ^ ISSN 1439-6092. Retrieved 2011-03-15.
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- ^ Temereva, E.N. (2000). "New phoronid species Phoronopsis malakhovi (Lophophorata, Phoronida) from the south China Sea". Zoologicheskii Zhurnal (in Russian). 79 (9): 1088–1093.
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External links
- PHORONIDA
- Phoronida World database
- Phoronidae – Guide to the Marine Zooplankton of south eastern Australia, Tasmanian Aquaculture & Fisheries Institute
- Bioerosion website at The College of Wooster