British insects: water beetles
Unless indicated otherwise, the following attributes are implicit throughout the descriptions, except where the characters concerned are inapplicable.
Adults. Beetles terrestrial. Beetles without the pairs of pronotal and elytral shining, hairy bumps characteristic of Macronychus (q.v.); not asymmetrically humped and tapered; without warning colouration; not luminescent; not conglobulating; not clicking and jumping; without a rostrum. The head not covered by the thorax.
Eyes present; two. Mandibles present. The maxillae without a conspicuous galea. The maxillae without stylet-like lobes. The maxillary palps relatively conspicuous. The maxillary palps not especially elongated. The maxillary palps not especially elongated. Antennae inserted further apart than the length of their first segment; not strongly asymmetric; not elbowed; without a much-elongated scape. Antennal scape not swollen. Antennal clubs not lamellate; not comprising two small basal segments and a large terminal one; without a cupule. Antennal segment 8 not smaller than 7 and 9.
The pronotum without five full length longitudinal furrows. The longitudinal ridges remaining well separated throughout their length. The pronotum without the pair of longitudinal furrows characteristic of Hydroglyphus, Bidessus et al. (q.v.). Metaventrite without a transverse groove. Mid-and hind-legs not as in Gyrinidae (q.v.). Hind coxae movable; not extended laterally to meet the elytra; not shaped posteriorly to receive the femur. The hind coxae not produced behind into flat plates partly concealing the hind femora. Hind coxae without the steep transverse declivity characteristic of Dryopoidea. The inner parts (processes) of the hind coxae not incorporated with the metasternum in a flat, median longitudinal keel. None of the tarsi with hidden segments. The front tarsi present and well developed; not each exhibiting a conspicuous, expanded rounded disc. Hind tarsi not flattened oar-like.
Elytra present; not individually tapered; meeting along the length of the mid-line; covering most to all of the abdomen; hard; not iridescent; not conspicuously longitudinally ribbed; without the small tooth near the tip that characterises Nebrioporus spp. Elytra not predominantly transversely striated across lines of puntured striae. Elytra not sculptured with numerous, short longitudinal cuts in a reticulated surface; lacking the pattern of longitudinal ridges characteristic of Stenelmis (q.v.). Wings well developed; not apically rolled; veined; not fringed. The end of the abdomen not extended as a long, narrow point beyond the ends of the elytra.
Larvae. The larvae neither strongly flattened nor disc-like; not C-shaped. The larval fronto-clypeus not extended forwardly.
The abdomen exhibiting functional abdominal spiracles; without spiracular tubes. The larvae without gills. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without a long median spine.
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: water beetles. Version: 18th September 2012. http://delta-intkey.com’.