GO:0070685

A cell projection that forms at the site of macropinocytosis, a form of endocytosis that results in the uptake of relatively large amounts of extracellular fluid. The macropinocytic cup membrane selectively excludes certain proteins, such as H36 or PM4C4 in Dictyostelium, and the underlying cytoskeleton is enriched in F-actin and coronin. [PMID:12538772, PMID:16968738, PMID:9044041]