Shortly before his death from a heart attack in 2015, Davidson co-authored a landmark review book providing a grand synthesis of the theory and experimental evidence relating to the design and function of genomic regulatory networks within the animal taxonomic clade of Bilateria.
32.
For instance, the gene Pax6 has a key role in eye development, but is absent in some animals with eyes; some cnidaria have genes which in bilateria control the development of a layer of cells that the cnidaria don't even possess.
33.
First, if all the microbiota in your body were to cease to exist, you'd suddenly find yourself cadaverous, unable to engage in the symbiotic metabolic biome they provided, and would be like a reef that had lost all its bilateria.
34.
It has been suggested that bilateral symmetry may have evolved before the split between Cnidaria and Bilateria, and that the radially symmetrical cnidarians have secondarily evolved radial symmetry, meaning the bilaterality in cnidarian species like " N . vectensis " has a primary origin.
35.
*I can't get behind the paywall, but what they are discussing is not traditional ranks like phylum or intermediate ranks like subphylum, but clades that were found not to fit in the traditional Radiate versus Bilateria dichotomy, and the Protostome versus Deuterostome dichotomy of the eucoelomate bilaterians.
36.
Various studies in this regard so far yield differing results for identifying the exact sister group : in one case the Placozoa would qualify as the nearest relatives of the Cnidaria, while in another they would be a sister group to the Ctenophora, and occasionally they are placed directly next to the Bilateria:
37.
:Recently this categorization of coelomate and acoelomate bilateria and the two great branches of protostomes and deuterostomes ( which are special because were are deuterostomes ) have been reshuffled, with the nematodes closer to the arthropods than the arthropods are to the annelids, with which they were once closely allied because they had segmented bodies.
38.
Deuterostomia is a subtaxon of the Bilateria branch of the subkingdom Eumetazoa, within Animalia, and are distinguished from protostomes by their deuterostomic embryonic development; in deuterostomes, the first opening ( the blastopore ) becomes the anus, while in protostomes, it becomes the mouth . ( There are some occurrences of deuterostomy among Protostomes .)
39.
In contrast to the model based on functional morphology described earlier, in the Epitheliozoa concept the ventral and dorsal cell layers of the Placozoa are homologs of endoderm and ectoderm, the two basic embryonic cell layers of the eumetazoans the digestive " gastrodermis " in the Cnidaria or the gut epithelium in the bilaterally symmetrical Bilateria may have developed from endoderm, whereas ectoderm is, among other things, the precursor to the external skin layer ( epidermis ).
