Editing Sea cucumber (section)

===Circulatory systems===
Like all echinoderms, sea cucumbers possess both a [[water vascular system]] that provides hydraulic pressure to the tentacles and tube feet, allowing them to move, and a ''haemal system''. The latter is more complex than that in other echinoderms, and consists of well-developed vessels as well as open [[Hemocoel|sinuses]].<ref name=IZ/>

A central haemal ring surrounds the pharynx next to the ring canal of the water vascular system, and sends off additional vessels along the radial canals beneath the ambulacral areas. In the larger species, additional vessels run above and below the intestine and are connected by over a hundred small muscular ampullae, acting as miniature hearts to pump blood around the haemal system. Additional vessels surround the respiratory trees, although they contact them only indirectly, via the [[Coelom#Coelomic fluid|coelomic fluid]].<ref name=IZ/>

Indeed, the blood itself is essentially identical with the coelomic fluid that bathes the organs directly, and also fills the water vascular system. Phagocytic coelomocytes, somewhat similar in function to the [[white blood cell]]s of [[vertebrates]], are formed within the haemal vessels, and travel throughout the body cavity as well as both circulatory systems. An additional form of coelomocyte, not found in other echinoderms, has a flattened discoid shape, and contains [[hemoglobin]]. As a result, in many (though not all) species, both the blood and the coelomic fluid are red in colour.<ref name=IZ/>

{{multiple image
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 | direction = vertical
 | width     = 220
 | image1    = Pearsonothuria graeffei bouche.JPG
 | alt1      = 
 | caption1  = ''[[Pearsonothuria graeffei]]'' showing its three rows of podia on its ''trivium''
 | image2    = Zeekomkommer-insluitselen.jpg
 | alt2      = 
 | caption2  = Sea cucumber ossicles (here "wheels" and "anchors")
}}

[[Vanadium]] has been reported in high concentrations in holothuroid blood,<ref>{{cite book | last = Phillips | first = Alexander |title = A Possible Source of Vanadium in Sedimentary Rocks | publisher =Princeton University | year = 1918 | url={{google books |plainurl=y |id=O6KxwrrC_LMC|page=473}}|page=473}}</ref> however researchers have been unable to reproduce these results.<ref>{{cite journal | last1 = Ciereszko | first1 = L. |title = On the Occurrence of Vanadium in Holothurians | year = 1962 |doi=10.1016/0010-406X(62)90034-8  |last2 = Ciereszko | first2 = E | last3 = Harris | first3 = E | last4 =Lane | first4 = C | journal = Comparative Biochemistry and Physiology |volume = 7 | issue = 1–2 | pages = 127–9 | pmid = 14021342}}</ref>