, in its simplest and least complex form, is the skeleton of primitive, more advanced, and in some common, modern day organisms.[1]
While more advanced organisms can be considered hydrostatic, they are
sometimes referred to as hydrostatic for their possession of a
hydrostatic organ instead of a hydrostatic skeleton. A hydrostatic organ
and a hydrostatic skeleton may have the same capabilities, but they are
not the same.[1]
Hydrostatic organs are more common in advanced organisms, while
hydrostatic skeletons are more common in primitive organisms. As its
name suggests, containing hydro meaning "water", being hydrostatic means
that the skeleton or organ is fluid-filled.<span>[2]
Arteries carry oxygenated blood away from the heart. Veins carry the blood back to the heart. Veins contain valves that ensure blood flows in only one direction. Arteries don’t require valves because pressure from the heart is so strong that blood is only able to flow in one direction.
