Work on cnidarians suggests that their Pax-6 ortholog may have evolved from an ancestral PaxB-like gene that duplicated after the separation of Bilateria
from Cnidaria (Kozmik et al.
Homeobox genes are involved in body plan formation and in the regulation of many developmental processes in bilateria
La evidencia sugiere que el conjunto completo de genes Hox ya se encontraba en el ancestro de toda la linea bilateria
, en el precambrico, estableciendo desde entonces el orden fundamental del plan corporal de este linaje (Maynard-Smith y Szathmary, 1999; Gould, 2002; Raff, 1996; Burke y Brown, 2003).
Evidence for a diverse cys-loop ligand- gated ion channel superfamily in early bilateria
Phylogenetic analysis of complete small subunit ribosomal RNA coding region of Myxidium lieberkuehni: evidence that Myxozoa are Metazoa and related to Bilateria
According to this divergence model, one or a few ancestral "eye genes," for example the regulatory gene Pax6, evolved in the ancestral bilateria
, resulting in the first eyespot.
Consideration of RNA secondary structure significantly improves likelihood-based estimates of phylogeny: examples from the Bilateria
On the other hand, Bilateria
, which include worms, mollusks, insects, and vertebrates, did not descend directly from this "spongy" ancestor.
The Invertebrates: Platyhelminthes and Rhynchocoela, the Acoelomate Bilateria
The Invertebrates: Echinodermata, the Coelomate Bilateria
Attempts to draw a linear evolutionary origin from cnidarians to the bilateria
will always be complicated by the differences in body symmetry and the resultant need for nervous system specialization related to those different body forms.
The Invertebrates: Smaller Coelomate Groups: Chaetognatha, Hemichordata, Pogonophora, Phoronida, Ectoprocta, Brachipoda, Sipunculida, the Coelomate Bilateria