Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Subgenital plate: A plate below the genitalia, which can arise from different structures or take a variety of forms in different taxa. For example, in mayflies, it may be a produced part of sternum VII. In stoneflies, it may refer to a part of sternum IX in males or VIII in females.
This other word references the same concept: subgenital plates.