Water-penny beetles
PsephenidaeSummary 1
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, 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.
SoCal Status 2
Only two Known Species per The California Beetle Database .
Eubrianax edwardsii
Psephenus falli
General description 3
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.
Physical description 4
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
Diversity 5
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.
Development 6
Female water penny beetles lay their eggs above or at the edge of the stream or shore habitat where their larvae will live. Aquatic larvae hatch from the eggs and drop or crawl into the water. They cling to gravel and other hard debris in the water, grazing on the algae and other micro-organisms that grow there. In this stage they grow and molt several times during warm months. If the warm season is short, they may need more than one year to complete the larval stage. When read to transform, larvae small chamber where they enter the pupal stage and metamorphose into an adult. Some species create an air-filled chamber under water, but most pupate on land, in moist soil. Pupation is completed inside the larval skin. Adults don't live long.
Development - Life Cycle: metamorphosis
Food habits 7
Water penny larvae feed on periphyton, the thin layer of algae and micro-organisms that forms on stones and other objects in moving freshwater. Adults may not feed.
Sources and Credits
- (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Psephenidae
- (c) BJ Stacey, some rights reserved (CC BY-SA)
- Adapted by BJ Stacey from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31418157
- Adapted by BJ Stacey from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/25066577
- Adapted by BJ Stacey from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/25066574
- Adapted by BJ Stacey from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/25066578
- Adapted by BJ Stacey from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/25066580
