What is "pleidae"

Pleidae, the pygmy backswimmers, is a family of aquatic insects in the order Hemiptera ( infraorder Nepomorpha, or "true water bugs"). There are 37 species in three genera, distributed across most of the world, except the polar regions and remote oceanic islands.

Pleidae belong to the Tripartita which contains the more advanced lineages of true water bugs, and are closely related to the true backswimmers (Notonectidae), but closer still to the Helotrephidae, another family of tiny Nepomorpha, which usually swim upside-down and, like the Pleidae, have a sensory organ in the center of the clypeus. Either the pygmy backswimmers are united with the Helotrephidae in the superfamily Pleoidea, or these two and the true backswimmers are placed in a single superfamily Notonectoidea.