Srivastava, Mansi Whitehead Institute for Biomedical Research, Cambridge, Massachusetts.
Rokhsar, Daniel S. Department of Molecular and Cell Biology, DOE Joint Genome Institute, Center for Integrative Genomics, University of California, Berkeley, California.
- Early animal evolution
- Slow-evolving genome
- Genes for animal development
- Genes for neurons
- Links to Primary Literature
- Additional Readings
Placozoans are small (1–2 mm), disk-shaped animals that were first discovered living on the walls of a saltwater aquarium in the late 1800s. After a long period of diminished interest, these animals were rediscovered in the 1970s amidst hypotheses that they might resemble the earliest animals. The only named species in the phylum Placozoa, Trichoplax adhaerens, is one of the simplest known animals, since only four cell types have been described. These cells are organized into an upper epithelium (with cover cells), a lower epithelium (with columnar and secretory cells), and a layer of multinucleate, contractile cells in the middle, but the overall form of the animal is amorphous, resembling a pancake (Fig. 1).
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