| Crawling water beetles | |
|---|---|
 | |
| Haliplus fluviatilis | |
 | |
| Peltodytes dispersus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Suborder: | Adephaga |
| Superfamily: | Haliploidea Aubé, 1836 |
| Family: | Haliplidae Aubé, 1836 |
| Genera | |
| |
TheHaliplidae are afamily ofwater beetles that swim using an alternating motion of the legs. They are therefore clumsy in water (compared e.g. with theDytiscidae orHydrophilidae), and prefer to get around by crawling. The family consists of about 200species in fivegenera, distributed wherever there isfreshwaterhabitat; it is the only extant member ofsuperfamilyHaliploidea. They are also known ascrawling water beetles orhaliplids.[1]
The adults of these beetles are generally oval in shape, with a very convex upperside, and are generally 1.5–5.0 mm (0.059–0.197 in) long. They are generally yellowish to light brown in color, frequently with light and dark patterns dotted with 10 or more rows of punctures on theelytra. The family's most distinctive characteristic is the largecoxal plates of the hindlegs, which are immobile (though not fused in the centerline) and extend back along the underside to cover most of theabdomen base and the hindleg trochanters and femora. They are used as air storage supplementing the air carried under the elytra.[1][2]
Thecompound eyes are markedly protruding from a smallish head, which bearsantennae with 11 segments set upon anantennophore with a conspicuously short base (scapus). The extension of theprosternum is broad, with a truncated tip, ending adjacent to themetasternal process. The metasternum has a complete transverse ridge. The slender legs have long swimming hairs on tibiae and tarsi, but are not flattened into "flippers". The foreleg tibiae lack the apparatus for antenna cleaning present in many other beetles. Unlike in otherAdephaga, the hindwings are not folded under the elytra, but rolled togetherapically.[1][2]
Haliplidaelarvae have a long and slender body with a toughexoskeleton. They can be recognized by their specializedmouthparts, carried on a small head. Themaxillae andlabium areadapted to manipulating thealgae the larvae feed on, while themandibles contain a channel through which fluids are sucked out of the food. The larval legs are short and carry a single claw each, but the forelegs have various adaptations for climbing amongwater plants.Respiration is viagills which are either long and filamentous, or (as inPeltodytes) shortmicrotracheal extensions; they are carried on thetergites of each thoracic segment and all but the ninth or tenth abdominal segment, whichever is terminal. The latter may be absent, but in the larvae of some Haliplidae it is tapering and ends in two prongs (which are noturogomphi though). The last (third)instar has functionalspiracles on themesothorax and the first to seventh abdominal segments.[2]
Haliplids live in the aquatic vegetation around the edges of small ponds, lakes, and quiet streams. Adults areomnivorous, eating insect eggs, smallcrustaceans,hydrozoan polyps, and algae, while thelarvae eat onlyalgae. The species ofPeltodytes depositeggs on the surface of aquatic plants, whileHaliplus chews out a cavity in the plants for their eggs. There are threeinstars, andpupation takes place on land in a chamber constructed by the larva.[1]
Crawling water beetles are not extensively studied because their interaction with humans is minimal.Hungerford's crawling water beetle (Brychius hungerfordi) is anendangered species found only inMichigan andOntario.[3]
The classification of haliplids as a separate group ofAdephaga is unquestioned, and mostentomologists believe they developed from terrestrial beetles separately from other types of water beetles. For many decades, the family was in need of revision, the last general catalog being published by A. Zimmermann in 1920. B. J. van Vondel produced an updated catalogue of the known Haliplidae taxa.[4]
Like predaceous diving beetles (Dytiscidae), the crawling water beetles form an early offshoot of the Adephaga. They still have groovedmaxillae and theirtentoriolacinial muscle does not attach to the mesal stipial base. Their larvae, like those of predaceous diving beetles, do not possess eggshell-bursters on the head. It is not yet resolved whether Haliplidae and Dytiscidae are closest relatives, or whether they originated independently from thebasal Adephaga.[2]
The family is not very diverse, with only fivegenera accepted.[5] Of these,Peltodytes is probably the most ancestral, though it has a number ofautapomorphies. The others have moresynapomorphies in common;Haliplus is the more diverse and appears to include some minor lineages formerly considered independent genera.[2]
