The sea cucumber is not a vegetable at all but a marine animal — a soft, sausage-shaped echinoderm, kin to the sea urchin and the starfish — that crawls slowly over the seabed grazing on detritus. In Chinese cuisine it is one of the great banquet luxuries, known as haishen, "sea ginseng," and is prized far less for flavour than for its springy, gelatinous texture and its long-standing reputation as a restorative tonic. It is almost always sold dried, then rehydrated over several patient days and braised, emerging mild, brothy and slippery-tender.