Psephenidae

Psephenidae is a family of beetles commonly known as water penny beetles. These insects are primarily found in freshwater habitats, particularly in well-oxygenated, flowing streams and rivers. Their most distinctive feature is their flattened, oval body shape, which resembles a coin or a penny, hence their common name. This morphology allows them to cling tightly to submerged rocks and substrates, resisting strong currents.

The larval stage of psephenids is also aquatic and highly specialized. Larvae possess a unique adaptation: a series of flattened, gill-bearing plates that extend laterally from their body segments. These plates are arranged in such a way that they create a suction effect, further aiding in their adherence to rocks and facilitating respiration in oxygen-rich water. Both larvae and adults are detritivores, feeding on algae, diatoms, and other organic matter found on submerged surfaces.

Adult psephenids are less commonly observed than their larvae, as they typically live a shorter adult lifespan and may spend more time out of the water, sometimes near the stream banks. They are generally poor fliers. The distribution of Psephenidae is widespread, with species found on most continents, though they are absent from Antarctica. Their presence is often considered an indicator of good water quality due to their sensitivity to pollution.