Group of animals with bilateral symmetry
The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.
Derived from two embryonic germ layers, the ectoderm and the endoderm. Lacks true mesoderm.
Having three germ layers. Used of the vertebrate embryo.
An animal that lacks a coelom. Acoelomates, which include the flatworm, fluke, tapeworm, and ribbon worm, exhibit bilateral symmetry and possess one internal space, the digestive cavity.
The central cavity of the gastrula, which ultimately becomes the intestinal or digestive cavity.
Characteristic of protostomes where cell division changes it from a four-cell embryo to an eight-cell embryo, the cells divide such that each cell in the top four cell plane is at an angle to the opposite cell in the bottom plane.
cleavage of an egg in which each division irreversibly separates portions of the zygote with specific potencies for further development
Characteristic of deuterostomes where cell division changes it from a four-cell embryo to an eight-cell embryo, the cells divide such that each cell in the top four cell plane is directly over one other cell in the bottom plane.