A study on the development of priapulids or ‘penis’ worms throws doubt on a feature that has been thought for more than 100 years to define the largest branch of the animal tree of life. Members of ...

Lynn Margulis classified the Chaetognaths, known as arrow worms, as deuterostomes. Deuterostomy is characterized by several developmental characteristics including radial, indeterminate cleavage, a ...

How humans evolved from the very first animals over the last 600 million years is an endlessly fascinating question. When piecing together the many steps leading from our first simple animal ancestor ...