The answer is a simple radial nervous system.
Echinoderms do not have brains. Around their mouth, they have central rings from which nerves radially run into arms and along the body. Movement is controlled by the branches of those radial nerves.
The answer would be letter a
Sponges have medicinal properties due to the presence of microbial chemicals that may control viruses, bacteria, tumors and fungi. They even look rather nice, and some species are helpful to humans when dried and put to use in the kitchen and bathtub.Up to 99% of the world's animal species are invertebrates.
The correct answer to this could be numerous words. The most broad term that would fit would be the Cosmos. If you are referring to more specific then you might be saying things such as Ionosphere. That is where Sputnik 1, the first satellite, was launched.
