Which family includes both water scavenger beetles and water penny beetles?

The family that includes both water scavenger beetles and water penny beetles is Hydrophilidae. This family is known for its diverse range of aquatic beetles that are adapted to living in freshwater environments. Water scavenger beetles, a subgroup within Hydrophilidae, are commonly found in still and slow-moving waters, where they play important roles in the decomposition of organic matter and nutrient cycling.

Water penny beetles, or larvae of the family Psephenidae, also inhabit aquatic ecosystems but belong to a different family and have distinct morphological traits and life cycles. Elmidae, another family mentioned, primarily consists of riffle beetles and does not encompass water scavenger beetles. Coleoptera, while it is the order that includes all beetles, is too broad to specifically identify the correct family shared by both water scavenger and water penny beetles. Thus, Hydrophilidae is the correct choice, as it specifically encompasses the aquatic adaptations and characteristics of the two beetle types mentioned.