The lymphatic circulation begins with blind ending (closed at one end) highly permeable superficial lymph capillaries, formed by endothelial cells with button-like junctions between them that allow fluid to pass through them when the interstitial pressure is sufficiently high. These button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF. There is another system of semilunar (semi = half; lunar = related to the Moon) valves that prevents back-flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections (anastomoses) between them and form a very fine network.

Answer this question: structure that prevents backflow of fluid in lymphatic vessels? Let's think fast. Stream of consciousness:
The relevant information is: There is another system of semilunar (semi = half; lunar = related to the Moon) valves that prevents back-flow of lymph along the lumen of the vessel. So the final answer is semilunar ( semi = half ; lunar = related to the Moon ) valves.