Hygrobia
Introduction '''''Hygrobia''''' is a genus of aquatic beetles native to Europe, North Africa, China and Australia. It is the only genus in the family '''Hygrobiidae''', also known as the '''Paelobiidae'''. These are known commonly as '''squeak beetles''' or '''screech-beetles'''.There are six known living species, with a highly disjunct distribution, and one extinct species, ''Hygrobia cretzschmari''.
Biology All species occur in lowland areas  and are mainly found in stagnant water. They live in the mud, silt, and detritus of ponds.None of the species occur in sympatry, except for ''H. nigra'' and ''H. australasiae'' in south-eastern Australia.Both adults and larvae are predators, specialized on oligochaete worms. The adults feed for as long as 30 min, coming to the surface very briefly to renew the air-supply.Adults are able to stridulate, producing an audible sound, which is why they are called squeak or screech beetles.
Morphology The body length ranges from 8.0 to 11.0 mm. Compound eyes are present, not divided into ventral and dorsal portions, strongly protruding. Labrum is short and transverse. The antennae are filiform, almost glabrous, with 11 segments.
Phylogeny and evolution The monophyly of the family is not in doubt.Hygrobiidae is thought to be the sister group to a clade comprising Dytiscidae (diving beetles), Amphizoidae (trout stream beetles) and Aspidytidae (cliff beetles), based on DNA sequence data.Regarding the relationships among the species of ''Hygrobia'', a recent phylogenetic analysis suggested a sister group relationship between ''H. hermanni'' and a clade formed by the Australian species, with ''H. nigra'' sister to ''H. australasiae. ''Hygrobiidae probably diverged from other Hydradephagan clades around the time of the initial breakup of Pangea. The split between today's Palearctic and Australian clades occurred later, possibly in the middle Mesozoic, by dispersal events.
Species diversity and distribution ''Hygrobia australasiae'' (Clark, 1862) - Australia''Hygrobia davidi'' Bedel, 1883 - Jiangxi, southeastern China''Hygrobia hermanni'' (Fabricius, 1775) - Europe, northern Africa (Morocco, Algeria and Tunisia), and Israel''Hygrobia maculata'' Britton, 1981 - Australia''Hygrobia nigra'' (Clark, 1862) - Australia''Hygrobia wattsi'' Hendrich, 2001 - Australia
Family name There has been a controversy associated with deciding which is the valid family name of squeak beetles: Hygrobiidae or Paelobiidae. Paelobiidae has priority over Hygrobiidae, but the latter name was until recently much more widely used.
References
External links * ''Hygrobia''. Fauna Europaea.