Animals that have a complete
tube-like gut with two openings​

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.