Water Penny Beetles


Summary 5

Water-penny beetles are a family (Psephenidae) of aquatic beetles. The young, which live in water, resemble pennies. The larvae feed off of algae, larvae, and feces. The presence of water penny larvae in a stream can be used as a test for the quality of the water. Among the pollution sensitivity categories sensitive, somewhat-sensitive, and tolerant; water pennies belong to the sensitive category. They cannot live in habitats where rocks acquire a thick layer of algae,...

General description 6

This small family of beetles gets its common name ("water pennies") from the unusual shape of the larvae, which have widely expanded dorsal plates that give the animals a flat round shape, like a coin. The classification of the family is uncertain, some authorities recognize some subgroups as separate families. There are only about 263 species in 31 genera are known (Lee et alia, 2007) but this family has not received intensive study, and there are probably more species still undescribed.

Morphology 7

Larvae are 3-10 mm long, ranging in color from pale amber to nearly black (usually matching the substrate) and have a distinctive shape. They dorso-ventrally flattened, with expansions of the dorsal plates that extend out so far that they are oblong or nearly round when viewed from above -- the head and legs completely covered. This flat round shape, plus their brownish color, earns them the name "water pennies". Larvae have clawed legs for clinging to rocks in moving water, and chewing mouthparts for scraping food off of rock and other hard substrate.

Adults are dark-colored, 4-6 mm long, with somewhat flattened bodies, short thread-like antennae, and mandibles not visible from above.

Most species in this family have amphipneustic larvae: they can extract oxygen both from air and directly from the water. They have a few functional spiracles for air breathing. Most also have filamentous gills that extract oxygen from the water, either paired structures on abdomenal sterna, or a single caudal structure near the anus. The genus Psephenoides is more fully aquatic, neither larvae nor pupae have functional spiracles, and both stages have gills. In the rest of the family, pupae and adults are air-breathers, with functional spiracles.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Habitat 8

Psephenid larvae cling to hard substrates (rocks, woody debris) in well-oxygenated water. They are most often found in fast-moving streams, especially riffle beds, but some species are found on rocky lake shores with wave action. Most pupae and all adults are air-breathing, but stay near the water. Adults are often found on the underside of logs and other objects overhanging streams.

Habitat Regions: temperate ; terrestrial ; freshwater

Aquatic Biomes: benthic ; rivers and streams; coastal

Other Habitat Features: riparian

Sources and Credits

  1. (c) Stroud Water Research Center, some rights reserved (CC BY), http://www.boldsystems.org/archive/image.php?id=bold.org/272638
  2. (c) Jaclyn McCormick, some rights reserved (CC BY-NC-SA), http://www.boldsystems.org/archive/image.php?id=bold.org/512213
  3. (c) anonymous, some rights reserved (CC BY-NC-SA), https://collections.nmnh.si.edu/services/media.php?env=ento&irn=9102162
  4. (c) anonymous, some rights reserved (CC BY-NC-SA), https://collections.nmnh.si.edu/services/media.php?env=ento&irn=9102273
  5. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Psephenidae
  6. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31418157
  7. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31418160
  8. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31418159

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