Question

Explain which layer, endoderm, mesoderm, or ectoderm, nervous, muscular, stomach, and skin develop from. 

What features of the fossil record suggest that during the Cambrian explosion, there was a rise of predator-prey relationships? 

What is most likely to have been the last common ancestor of all? What are the key characteristics of arthropods? 

Why do planarians lack dedicated respiratory and circulatory systems?

Answer 1

Nervous system develops from ectoderm, the outer most layer of embryo.neuro ectoderm appears in third week of an embryo development.Muscular develops from mesoderm layer which consists of cardiac , smooth and skeletal muscles.Stomach develops from endoderm, And skin develops from epidermis which is an ectoderm layer.

The adaptation which which rose in cambrian were protection and predation.Much of the parts were hard like exoskeleton and shells which fosilize well.

Urbilaterian is the last common ancestor of all , which lived 700 billion years ago.Arthropods are invertebrates,it has open circulatory system, jopint appendages, bilateral symmetry.These are the key characteristics of arthropods.

Planarians lack respiratory system and circulatory system because none of the cells are removed from the gastrovascular from the external environment.