GENERAL HISTOLOGY

Detailed explanation-1: -Protraction of the foot is made possible by the contraction of the ampulla musculature. The fluid within the ampulla cavity is driven into the podium which elongates by reason of the increased pressure within its cavity. During protraction the longitudinal muscles of the foot relax.

Detailed explanation-2: -The podium is the tube-shaped structure that protrudes from the body and contains longitudinal muscle only. When the muscles around the ampulla contract, they squeeze water from the ampulla into the connected podium, causing the podium to elongate.

Detailed explanation-3: -Ampullae: A pouch or sack-like part of the sea star’s water vascular system that expands and contracts to move water up and down each tube foot. When the sea star wants to create a suction at the end of its tube foot, its ampullae pulls water out of the podia.

Detailed explanation-4: -How do the ampullae and tube feet act to affect locomotion. The ampullae contracts, sending water into the tube feet which stretch as water is brought into them. Thus, allowing for a slow form of locomotion.