Water vascular system

The water vascular system (WVS) is a hydraulic system characteristic of all echinoderms (Ruppert et al. 2004). It is used in prey manipulation, gas exchange, locomotion and adhesion (Ruppert et al. 2004). The WVS is lined with myoepithelium, making it ciliated and muscularised (Ruppert et al. 2004).  This allows for the movement of water throughout the system. Water enters the system, from the external environment, via the pores in the madroporite (Ruppert et al. 2004). The madroporite is connected via the stone canal to the ring canal (Ruppert et al. 2004). Water enters the madroporite through the inward ciliary beating, and even though the ciliary beating is bidirectional, the inward beat is strong enough to overwhelm the opposing cilia (Ruppert et al. 2004). 

The ring canal possesses five joining radial canals, extending into each arm of the starfish (Ruppert et al. 2004). These radial canals possess multiple ampullae radiating from the central radial canals, connected by lateral canals which all possess valves (Ruppert et al. 2004). Each of these ampullae possesses a podia, or tube foot. The tube feet are often modified to possess a sucker at the anterior end (Ruppert et al. 2004). Tube feet are the primary site of water lost through in the WVS, as they are known to be leaky (Ruppert et al. 2004). As a result, fluid recovery via the madroporite is essential (Ruppert et al. 2004). Water recovery is also possible in the tube feet.
Due to the high concentrationof potassium (K⁺) ions present in the WVS, the osmotic gradient present between the WVS and the external environment causes an influx of seawater across the tube feet (Ruppert et al. 2004). 

Additional structures present within the WVS are the Tiedemanns bodies and the Polian vesicles (Ruppert et al. 2004). Tiesmanns bodies function in removing bacteria and other unwanted particles from the WVS, which may have been missed by cilia at the surface of the madroporite (Ruppert et al. 2004). The Polian vesicles are thought to act as fluid storage, however this is only a hypothesis (Ruppert et al. 2004). 

Starfish Water Vascular system, ​modified from Ruppert et al. (2004)

Locomotion

Locomotion of all starfish, including N.cumingi occurs through the use of the water vascular system (Ruppert et al. 2004). The movement of water and consequent hydraulic pressure causes three processes to occur in the tube feet which allow movement of the legs (Ruppert et al. 2004). These include: extension-attachment, force generation, and detachment-retraction (Ruppert et al. 2004). Extention-attachment occurs through the extension of the longitudinal muscles, which lines the ampullae and tube feet (Ruppert et al.2004). This contraction in addition to closure of the valve in the lateral canal forces the water in to the tube foot resulting in an elongation of the tube foot (Ruppert et al. 2004).  Upon contact of the tube foot with the substrate the sucker attaches through the aid of chemicals secreted by the tube feet which cause it to bond to the surface.  The secretion of a second chemical breaks this chemical bond allowing the tube feet to detach (Ruppert et al. 2004).  Following attachment of the sucker to the substrate, the longitudinal muscles contract causing a pulling force to be exerted (Ruppert et al. 2004). This contraction causes the water to travel to the ampullae and results in the retraction of the tube feet (Ruppert et al. 2004). This continual movement of the tube feet can be seen in the following video.