 Nuclear receptors are specific to metazoans (animals) and are not found in protists, algae, fungi, or plants.Amongst the early-branching animal lineages with sequenced genomes, two have been reported from the sponge "Amphimedon queenslandica", two from the ctenophore "Mnemiopsis leidyi" four from the placozoan "Trichoplax adhaerens" and 17 from the cnidarian "Nematostella vectensis".There are 270 nuclear receptors in the nematode "C. elegans" alone, 21 in "D. melanogaster" and other insects, 73 in zebrafish.