With approximately 98Mb Trichoplax adhaerens possesses the smallest genome of all known metazoan genomes. It has recently been sequenced [1]. In sharp contrast to the simple morphology, placozoans harbor rich complements of genes of almost all developmental pathways found in higher animals. Trichoplax harbors representatives for almost 80% of the ~7,800 core eumetazoan gene families that are conserved between the sea anemone Nematostella vectensis and bilaterian animals [2].
We are currently sequencing multiple placozoan genomes using high throughput sequencing techniques. The first placozoan genomes revealed some unexpected high diversity and suggest that Trichoplax adhaerens may not be the best-suited placozoan species for future research (see figure below).

legend: Whole genome comparison (in addition to whole mitochondrial genomes). Shown is a preliminary tree derived from protein coding nuclear and mitochondrial genes. The undescribed species Placozoa spec. nov. II must be the best-suited model system for comparative research.

1. Srivastava M, Begovic E, Chapman J, Putnam NH, Hellsten U, et al. (2008) The Trichoplax genome and the nature of placozoans. Nature 454: 955-U919.
2. Putnam NH, Srivastava M, Hellsten U, Dirks B, Chapman J, et al. (2007) Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization. Science 317: 86-94. 

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