Explain how a starfish's body plan and anatomy enables invertebrate to perform the essential functions it needs to survive.

Invertebrates are known as creatures that do not have backbones. Even though these creatures do not have backbones, they have been uniquely designed in order to survive. According to studies, most of these creatures are found in the sea and one of them is the Star Fish or also called as the Sea Star. Starfish's functions and ability to survive is not the same like other animals which make them unique in a different way. The starfish's body is hard and bony for protection purposes and they exist in a variety of colors for camouflage. Their essential functions in order to survive are as follows:
-The Ability to Regenerate: Starfishes have the ability to grow damaged and lost limbs or even their entire body as long as the center part is still present and intact. And this is their way of reproduction as well.
-Having Tube Feet: Its arms are covered with a suction-like tiny cups of tube feet. This unique design of the starfishes enables them to move and secure themselves, especially on rocks and ocean floors.
-Unique Feeding Ability: Sea Stars don't have mouths nor teeth to ingest food. Rather, these creatures have the ability to push open or turn their stomachs out and digest its food. After digestion, their stomachs retract back to their bodies. 
-Vascular System: How starfishes survive does not rely on having hearts, brains and blood. Rather, they use the seawater. The seawater serves as the one the circulates inside the sea stars' bodies and this is when nutrients and oxygen are being transported and absorbed. 

Gravitational force i believe