British insects: the families of Coleoptera
Adults. Beetles terrestrial to sub-aquatic; walking in water or free-swimming by conventional ambulatory motion of the legs, not diving strongly; moving in the water by alternate, walking leg movements. Beetles 1.5–1.8 mm long; body length/maximum body width 1.3–2.55. Beetles somewhat waisted. The head covered by the thorax (hiding the antennae and palps, and the pronotum anteriorly crinkled).
Eyes two; not strongly protuberant; without bristles. Mandibles with a well developed mola; with well developed prosthecae. The maxillae with distinct galea and lacinia apically to the palp. The maxillary palps conspicuously elongated, sometimes longer than the antennae. The maxillary palps conspicuously elongated, sometimes longer than the antennae. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae very short; not strongly asymmetric. Antennal scape not swollen. Antennae clubbed. Antennal clubs 3 segmented (the club hairy). Antennal insertions visible from above, or hidden from above.
Prothorax without notopleural sutures. The pronotum not narrowing towards the rear. Mid-and hind-legs not as in Gyrinidae (q.v.). Hind coxae 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. Tarsal segmentation formula 4, 4, 4. None of the tarsi with hidden segments. The front tarsi with as many segments as the mid-tarsi; 4-segmented; apical segment shorter than the rest together. Mid-leg tarsi 4-segmented; pseudotetramerous (?). Hind tarsi without swimming hairs. Swimming hairs confined to the tarsi.
Adults not predacious. In crumbly damp silt by running water, and in sand pits.
Larvae. The larvae elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; only very lightly pigmented or sclerotized; only very lightly pigmented. The antennae 3 segmented. Stemmata 6. Frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 4 segmented. The labium without ligula between the palps. The labial palps 4 segmented. The mesothoracic legs 3 segmented; with 1 movable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal.
The larvae aquatic. The abdomen exhibiting functional abdominal spiracles; having functional spiracles on anterior segments; with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The larvae predacious.
Worldwide and British representation. 1 species in Britain (G. crenulatus, terrestrial). Recorded from scarce, Scotland, Northern England, South-west England and Wales, and South-eastern England.
Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Hydrophiloidea; Hydrophilidae; Subfamily Georyssinae.
General comments on this taxon. Maxillary palps longer than the antennae.
Miscellaneous. • Georyssus crenulatus (from Joy, 1932). • Georyssus crenulatus, with Dryopidae, Elmidae and Heteroceridae: Fowler 3, 98 (1889).
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’.