Placozoa

Cross references:  Last Universal (Common) Ancestor 
Prokaryotes    Prokaryote Colonies    
Eukaryotes    Eukaryote Colonies    Slime Molds     Metazoa    
Parazoa    Porifera     Coelenterata    

Searching Google for "placozoa" uncovered 2,300,000 references: 
https://www.google.com/search?q=Placozoa&ie=utf-8&oe=utf-8   


Placozoa  (Wiki) 
http://en.wikipedia.org/wiki/Placozoa 
"The Placozoa are a primitive form of invertebrate.  They are the simplest in structure of all non-parasitic multicellular animals (Metazoa). They are generally classified as a single species, Trichoplax adhaerens, although there is enough genetic diversity that it is likely that there are multiple, morphologically similar species." 

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 Searching Google for "trichoplax" reveraled 209,000 refereences:   
https://www.google.com/search?q=+Trichoplax&ie=utf-8&oe=utf-8   
   

Trichoplax (Wiki) 
http://en.wikipedia.org/wiki/Trichoplax 
    "Trichoplax adhaerens is the only extant representative of phylum Placozoa, which is a basal group of multicellular animals (metazoa). Trichoplax are very flat creatures around a millimeter in width, lacking any organs or internal structures. They have three cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells which possess cilia used in locomotion and gland cells which lack cilia.[1] Between these layers is the fiber syncytium, a liquid-filled cavity strutted open by star-like fibers.   
    Trichoplax feed by absorbing food particles—mainly microbes—with their underside. They generally reproduce asexually, by dividing or budding, but can also reproduce sexually. Trichoplax has a small genome in comparison to other animals. Nearly 87% of its 11,514 predicted protein-coding genes are identifiably similar to known genes in other animals."  

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Genome Of Simplest Animal Reveals Ancient Lineage (Wiki)
http://www.sciencedaily.com/releases/2008/08/080820163002.htm   
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"The latest and most complex analysis again suggests that placozoans populated the oceans long before sponges evolved."   "Trichoplax is an ancient lineage—a good representation of the ancestral genome that is shedding light of the kinds of genes, the structures of genes, and even how these genes were arranged on the genome in the common ancestor 600 million years ago"    "Trichoplax is a two-millimeter flat disk containing fluid sandwiched between two cell layers. It lacks organs and only has four or five cell types. Yet, despite its apparent simplicity, its genome encodes a panoply of signaling genes and transcription factors usually associated with more complex animals."


Placozoa (Goog) 

http://www.newworldencyclopedia.org/entry/Trichoplax
     "Placozoans are the simplest in structure of all known multicellular animals (Metazoa). In addition, Trichoplax adhaerens has the smallest amount of DNA yet measured for any animal sequenced."
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    Contents
1 Overview
2 Structure
2.1 Epitheloid
2.2 Fiber syncytium
3 Distribution and habitat
4 Feeding and symbionts
5 Locomotion and behavior
6 Regeneration
7 Propagation
8 Role as a model organism
9 Genetics
10 Phylogenesis
10.1 Functional-morphology hypothesis
10.2 Epitheliozoa hypothesis
10.3 Eumetazoa hypothesis
11 References
11.1 First descriptions
12 External links
13 Credits



The : Trichoplax: genome and the nature of placozoans (Google) - 2008 
http://www.nature.com/nature/journal/v454/n7207/full/nature07191.html   
Full length HTML available online for free. 
    "Trichoplax appears as a flat disc of cells consisting of two epithelial layers, which sandwich a layer of multinucleate fibre cells (Fig. 1a). Only four cell types have been described previously8, 9 (Fig. 1b); nerves, sensory cells and muscle cells are apparently absent. To feed, Trichoplax climbs atop its food using the bottom surface as a temporary extraorganismal gastric cavity; digestion is both extracellular and phagocytic10, 11. When not feeding, the animals move by cilia on the bottom surface and by the fibre cell layer10. "  
     "Here we report the draft nuclear genome sequence of Trichoplax adhaerens and use it to begin to address the nature of placozoans. Our phylogenetic analysis supports the identification of placozoans as a basal eumetazoan lineage that diverged before the separation of cnidarians and bilaterians but after the divergence of demosponges from other animals. The compact genome shows remarkable complexity, including conserved gene content, gene structure and synteny relative to human and other eumetazoan genomes. Despite the absence of any known developmental program and only a modest number of cell types, the Trichoplax genome encodes a rich array of transcription factors and signalling genes that are typically associated with embryogenesis and cell fate specification in eumetazoans, as well as other genes that are consistent with cryptic patterning of cells, unobserved life history stages and/or complex execution of biological processes such as fission and embryonic development in these enigmatic creatures."  








CotA Placazoa 
160730 - 1334 


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