![]() They are therefore extremely sensitive to water pollution and are potentially valuable bioindicators for measuring the health of river ecosystems. īecause of their reliance on the plastron for breathing, spider water beetles are restricted to the highly oxygenated environments in moderate to fast-moving permanent running water. As the insect breathes, the oxygen concentration in the gas film drops in comparison to the surrounding water, causing new oxygen to diffuse again into the plastron. Spider water beetle adults, like all members of the subfamily Elminae, can also remain indefinitely underwater by means of a plastron, a thin film of gas trapped by hydrophobic bristles ( setae) on their body. They can be found crawling along or clinging with their claws on boulders or submerged wood in lotic riffles of streams and rivers. Like almost all riffle beetles, spider water beetles are aquatic, feeding on algae and decaying wood tissue. This fast-flowing and unpolluted mountain creek in Palawan, Philippines is the type locality of Ancyronyx montanus Īncyronyx is closely related to the genus Podelmis, but can be distinguished from the latter by the more or less straight and slender last segment of the ovipositor (versus the conical sideways-bent terminal segment of the ovipositor of Podelmis), and the absence of an anterior process on the prosternum. Their larvae are smaller, with a more vaulted cross-section, and backwards pointing projections from the sides of the abdomen. The Ancyronyx patrolus species group have small and slender bodies, with comparatively shorter legs, long and slender coxites on the ovipositor, and a squarish prosternal process. ![]() Their larvae are also larger, depressed in cross-section, and possess large side-pointing projections on the sides of the abdomen. The Ancyronyx variegatus species group are larger in size (usually larger than 1.4 mm (0.055 in)), with very long legs, stout coxites on the ovipositor, and a transverse prosternal process.Spider water beetles can be divided into two species groups, based on morphological and ecological adaptation patterns. The pronotum possesses a transverse groove and a more or less straight front margin, with pronotal carinae absent or weakly present. The elytra also possess eight to eleven grooves (elytral striae), as well as small depressions (elytral punctures) of varying depth and number. ![]() Most of the species possess brightly colored patterns on their elytra, but not all. ![]() The pair of antennae are typically 11-segmented. The legs are tipped with large claws, each with two or three basal teeth. The legs have widely separated coxae, with the procoxae (coxae attached to the prothorax) usually visible dorsally. They are characterized by extremely long legs (longer than the body length). They are typically very small, with an average body length (without legs) of 1 to 2 mm (0.039 to 0.079 in). Members of Ancyronyx superficially resemble spiders and are aquatic, hence their common name, "spider water beetles". It is the sole member of the tribe Ancyronychini, and is classified under the subfamily Elminae of the riffle beetle family, Elmidae. It was regarded as a monotypic species until the French entomologist Antoine Henri Grouvelle described the second species, A. The genus Ancyronyx was established in 1847 by the German entomologist Wilhelm Ferdinand Erichson based on the type species Macronychus variegatus first described in 1824 by the German coleopterologist Ernst Friedrich Germar. The genus contains twenty-one species, eleven of which are endemic to the Philippines. They feed on algae and decaying wood tissue. Both the adults and the larvae are found underwater in the shallow riffles of streams and rivers, clinging to rocks or submerged wood. They are small beetles with extremely long legs ending in strong claws. Ancyronyx, commonly known as spider water beetles or spider riffle beetles, is a genus of aquatic riffle beetles from North America, South Asia, China, and Southeast Asia.
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