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(Redirected from Placozoan)
'''Trichoplax adhaerens''' is a simple balloon-like marine animal with a body cavity filled with pressurized fluid. It is given its own phylum, called 'Placozoa'; the only other species assigned to this taxon, ''Treptoplax reptans'', was described in 1896 and has not been seen since, leading to doubts about its existence.
Individual ''Trichoplax'' are soft-bodied, about 0.5 mm across, and somewhat resemble a large amoeba. The name ''T. adhaerens'' was given because it tends to stick to its substrate, including glass pipettes and microscope slides. Its evolutionary relationships are still being investigated, but it may be allied with the cnidarians and ctenophores. Dellaporta ''et al'' have reported the complete mitochondrial genome sequence of ''Trichoplax adhaerens'' and showed that Placozoa are the most basal (that is, they branched off earliest) living eumetazoan phylum.[1]
''Trichoplax'' lacks organs and most tissues, including nerve cells and a nervous system, although evidence suggests that they evolved from species with nerve cells. It is made up of a few thousand cells of four types in three distinct layers: monociliated dorsal and ventral epithelia cells, ventral gland cells and the syncytial fiber cells. The outermost layer (the monociliated cells) have a single cilium, which allow the adult to move. The epithelia of ''Trichoplax'' lack a basal membrane and the cells are connected by belt desmosomes. Lipid inclusions, called 'shiny spheres', are regularly distributed over the dorsal epithelia.
It feeds by absorption and has been observed to form temporary bulges to trap food. It climbs atop its food and uses the ventral surface as a temporary extraorganismal gastric cavity. Digestion is both extracellular and by phagocytosis.
When not feeding ''Trichoplax'' is actively motile with movement effected by ventral ciliation and by the fiber cell layer and lacks any polarity in its movement.
The haploid number of chromosomes is six. It has the smallest amount of DNA yet measured for any animal with only 50 megabases (80 femtograms per cell). A trichoplax genome project is currently underway.[2]
Putative eggs have been observed, but they degrade at the 32-64 cell stage. Neither embryonic development nor sperm have been observed, however ''Trichoplax'' genomes show evidence of sexual reproduction.[3] Asexual reproduction by binary fission is the primary mode of reproduction observed in the lab.
''Trichoplax'' were discovered on the walls of a marine aquarium in the 1880s, and have rarely been observed in their natural habitat.[4] The full extent of their natural range is unknown, but they are easily collected in tropical and subtropical latitudes around the world.
If several Trichoplax are placed in the same dish they interact with each other. Movies of such interactions can be viewed here [1]
1. 'Mitochondrial genome of Trichoplax adhaerens supports Placozoa as the basal lower metazoan phylum', Dellaporta ''et al'', , , Proceedings of the National Academy of Sciences, 2006
2. ''Trichoplax'' genome project
3. Molecular signatures for sex in the Placozoa, Signorovitch AY, Dellaporta SL, Buss LW, , , Proceedings of the National Academy of Sciences, 2005
4. Occurrence in the field of a long-term, year-round, stable population of placozoans, Maruyama YK, , , Biol Bull, 2004
★ The Trichoplax Genome Project at the Yale Peabody Museum
★ A Weird Wee Beastie: Trichoplax adhaerens
★ Information page from the University of California at Berkeley
★ Mitochondrial DNA and 16S rRNA analysis and phylogeny of ''Trichoplax adhaerens'': full text online article .
★ Historical overview of Trichoplax research
'''Trichoplax adhaerens''' is a simple balloon-like marine animal with a body cavity filled with pressurized fluid. It is given its own phylum, called 'Placozoa'; the only other species assigned to this taxon, ''Treptoplax reptans'', was described in 1896 and has not been seen since, leading to doubts about its existence.
Individual ''Trichoplax'' are soft-bodied, about 0.5 mm across, and somewhat resemble a large amoeba. The name ''T. adhaerens'' was given because it tends to stick to its substrate, including glass pipettes and microscope slides. Its evolutionary relationships are still being investigated, but it may be allied with the cnidarians and ctenophores. Dellaporta ''et al'' have reported the complete mitochondrial genome sequence of ''Trichoplax adhaerens'' and showed that Placozoa are the most basal (that is, they branched off earliest) living eumetazoan phylum.[1]
''Trichoplax'' lacks organs and most tissues, including nerve cells and a nervous system, although evidence suggests that they evolved from species with nerve cells. It is made up of a few thousand cells of four types in three distinct layers: monociliated dorsal and ventral epithelia cells, ventral gland cells and the syncytial fiber cells. The outermost layer (the monociliated cells) have a single cilium, which allow the adult to move. The epithelia of ''Trichoplax'' lack a basal membrane and the cells are connected by belt desmosomes. Lipid inclusions, called 'shiny spheres', are regularly distributed over the dorsal epithelia.
It feeds by absorption and has been observed to form temporary bulges to trap food. It climbs atop its food and uses the ventral surface as a temporary extraorganismal gastric cavity. Digestion is both extracellular and by phagocytosis.
When not feeding ''Trichoplax'' is actively motile with movement effected by ventral ciliation and by the fiber cell layer and lacks any polarity in its movement.
The haploid number of chromosomes is six. It has the smallest amount of DNA yet measured for any animal with only 50 megabases (80 femtograms per cell). A trichoplax genome project is currently underway.[2]
Putative eggs have been observed, but they degrade at the 32-64 cell stage. Neither embryonic development nor sperm have been observed, however ''Trichoplax'' genomes show evidence of sexual reproduction.[3] Asexual reproduction by binary fission is the primary mode of reproduction observed in the lab.
''Trichoplax'' were discovered on the walls of a marine aquarium in the 1880s, and have rarely been observed in their natural habitat.[4] The full extent of their natural range is unknown, but they are easily collected in tropical and subtropical latitudes around the world.
If several Trichoplax are placed in the same dish they interact with each other. Movies of such interactions can be viewed here [1]
| Contents |
| References |
| External links |
References
1. 'Mitochondrial genome of Trichoplax adhaerens supports Placozoa as the basal lower metazoan phylum', Dellaporta ''et al'', , , Proceedings of the National Academy of Sciences, 2006
2. ''Trichoplax'' genome project
3. Molecular signatures for sex in the Placozoa, Signorovitch AY, Dellaporta SL, Buss LW, , , Proceedings of the National Academy of Sciences, 2005
4. Occurrence in the field of a long-term, year-round, stable population of placozoans, Maruyama YK, , , Biol Bull, 2004
External links
★ The Trichoplax Genome Project at the Yale Peabody Museum
★ A Weird Wee Beastie: Trichoplax adhaerens
★ Information page from the University of California at Berkeley
★ Mitochondrial DNA and 16S rRNA analysis and phylogeny of ''Trichoplax adhaerens'': full text online article .
★ Historical overview of Trichoplax research
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