Flattened platelets with filopodium-like structures at the bottom of the thrombus. (A) Scanning electron microscopic image of platelets after experimentally induced ex vivo thrombus formation on collagen. White arrow indicates a filopodium; black arrowhead indicates collagen fiber. Scale bar, 4 µm. (B) Platinum replica of platelets after experimentally induced ex vivo thrombus formation on collagen. White arrow indicates a filopodium with unbranched actin filaments. Scale bars, 1 and 2 µm.