Water-penny beetles are a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

(the Psephenidae) of 272 species (in 35 genera) of aquatic beetles found on all continents except Antarctica, in both tropical and

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

areas. The young, which live in water, resemble tiny

pennies A penny is a coin ( pennies) or a unit of currency (pl. pence) in various countries. Borrowed from the Carolingian denarius (hence its former abbreviation d.), it is usually the smallest denomination within a currency system. Presently, it is th ...

. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e feed – usually nocturnally – on

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

e on rock surfaces. The presence of water-penny larvae in a stream can be used as a test for the quality of the water, as they are pollution-sensitive. They cannot live in habitats where rocks acquire a thick layer of algae, fungi, or inorganic sediment. Therefore, their presence along with other diverse phyla signifies good-quality water. They are around 6 to 10 millimeters in length. A water-penny larva's shell is oval-shaped to almost circular and is commonly a copper color, which explains the name, 'water-

penny A penny is a coin ( pennies) or a unit of currency (pl. pence) in various countries. Borrowed from the Carolingian denarius (hence its former abbreviation d.), it is usually the smallest denomination within a currency system. Presently, it is t ...

'. Water-pennies obtain oxygen through their membrane and through feathery gills located at the base of the abdomen. They are typically found in

riffle A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...

s in streams with a moderate to fast current, clinging to the underside of logs or rocks. Occasionally, they can be found on rocks along the shores of lakes. Attached to the legs are scrapers, which are used to scrape the algae from the surface of a log or rock. In North America, they are usually found in the

Northeast The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each se ...

, and occasionally discovered in the

Southwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sepa ...

. Some genera in the US: Usinger, Robert, L., 1956, ''Aquatic Insects of California'', p. 365. * '' Psephenus'': the Northeast and the

west coast West Coast or west coast may refer to: Geography Australia * Western Australia *Regions of South Australia#Weather forecasting, West Coast of South Australia * West Coast, Tasmania **West Coast Range, mountain range in the region Canada * Britis ...

(from Oregon to California; usually below 4,000 feet elevation in California). * '' Eubrianax'': California, up to 6,000 feet elevation. * '' Ectopria'': the northeastern and Central U.S. * '' Acneus'': California and Oregon up to 4,000 feet. As adults, water-pennies become terrestrial. Adults are relatively short lived and eat little to nothing.

Fossil genera

* Subfamily Eubrianacinae Jacobson 1913 ** †'' Succinumanax'' Bao et al. 2018

Burmese amber Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 100 million years ago, during the latest Albian to earliest Cenomanian ages of the mid-Cretaceous period. The ...

, Myanmar,

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

** †'' Vetujinbrianax'' Cai and Huang 2018 Burmese amber, Myanmar, Cenomanian * †'' Protacnaeus'' Wickham 1914

Florissant Formation The Florissant Formation is a sedimentary geologic formation outcropping around Florissant, Teller County, Colorado. The formation is noted for the abundant and exceptionally preserved insect and plant fossils that are found in the mudstones and ...

, Colorado,

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

* †'' Psephenella'' Martins-Neto 1998

Tremembé Formation Tremembé is a municipality in the state of São Paulo in Brazil. It is part of the Metropolitan Region of Vale do Paraíba e Litoral Norte. The population is 47,714 (2020 est.) in an area of 191.09 km². The elevation is 560 m. A shr ...

, Brazil,

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

References

External links

*
Video of a water-penny from Thailand
{{Authority control Byrrhoidea Aquatic insects