Sea urchin

The sea urchin is another interesting creature (Green circle, yellow circle = divergence time):

PIC

It provides valuable knowledge for cancer, Alzheimer's and infertility research:

Sea Urchins' Genetics Add To Knowledge Of Cancer, Alzheimer's And Infertility


What is even more interesting is what lurks in its genome. According to present models, they originated at least 450 million years ago. These organisms have no eyes, ears or a nose, yet they have the genes humans have for vision, hearing and smelling (see above link). They also have a surprisingly complex immune system, which surpasses the human one by far.

Now the genes in the genetic toolkit (nice video) in animals responsible for assigning specific properties of the various body parts are known as Hox genes. Here is a nice overview of Hox genes. A great deal of Hox genes are found in the sea urchin, the pattern of gene expression just differs, resulting in a different body plan.

Right at the base of the animal tree, a sundry of genes necessary for sight, smell, hearing as well as the various body plans were present in the genome of the common ancestor.