Any of numerous extinct marine arthropods of the class Trilobita, of the Paleozoic Era, having a segmented body divided by grooves into three vertical lobes and found as fossils throughout the world.

• 三叶虫多种构成三叶虫纲任一种的已灭绝的海洋节肢动物，身体分节，有带沟将身体一分为三个垂直的叶，在世界各地都发现过其化石