British insects: the families of Coleoptera
Adults. Beetles terrestrial, or sub-aquatic (? - living in or on mud on the margins of water courses); 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; perhaps replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron (?); perhaps incorporating bubbles of oxygen directly into the plastron (?). Beetles 1.5–1.8 mm long; body length/maximum body width 1.3–2.15; base of prothorax not or scarcely narrower than the combined elytral bases. Beetles oval; dorsally strongly convex; having ventral body cavities into which the legs fold to conform with the general body surface; not necked; not waisted. Upper surfaces of body not bristly; with neither scales nor scale-like setae.
Eyes two; strongly protuberant, or not strongly protuberant; without bristles. Mandibles with a well developed mola; with well developed prosthecae. The mandibular apices bidentate or bilobed, or multidentate or multilobed. The incisor edges of the mandibles simple. The maxillae with distinct galea and lacinia apically to the palp. The maxillary palps scarcely visible, being very much shorter than the antennae; not especially elongated. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae short; not strongly asymmetric; 7 segmented, or 11 segmented (?). Antennal scape not swollen. Antennae weakly clubbed. Antennal clubs 1 segmented. Antennal insertions visible from above, or hidden from above.
Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.3–0.65. The scutellum elevated. Metaventrite with a transverse groove, or without a transverse groove. Mid-and hind-legs not as in Gyrinidae (q.v.). The fore-leg coxal cavities broadly open; quite widely separated; strongly transverse; without lateral extensions; internally open. Hind coxae not extended laterally to meet the elytra; posteriorly shaped to receive the retracted femur. The hind coxae not produced behind into flat plates partly concealing the hind femora. Hind coxae with a steep transverse declivity against which the femur retracts. The inner parts (processes) of the hind coxae not incorporated with the metasternum in a flat, median longitudinal keel. Tarsal segmentation formula 5, 5, 5. None of the tarsi with conspicuously bilobed segments. None of the tarsi with hidden segments. The front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi with at least as many segments as the mid-tarsi; 5-segmented.
Elytra present. Elytral length/maximum width across the elytra 1–1.65. Elytra exposing no more than part of the terminal tergite. Scutellary striole absent. Elytra non-glabrous (with very short, fine recumbent pubescence). Wings well developed, or absent or much reduced. Exposed abdominal sternites 5; comprising both fused and movable components, or all fused and immovable; immovably joined 3, or 5. Abdominal segment 8 with apparently functional spiracles.
Found beside running water.
Larvae. The larvae campodeiform; elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; dorsally heavily pigmented or sclerotized; only very lightly pigmented. The antennae 3 segmented; less than 0.15 x the with of the head. Frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles bilobed or bidentate, or trilobed or tridentate (?). The maxillary palps 4 segmented. The labium with a short ligula between the palps. The labial palps 4 segmented. The mesothoracic legs 5 segmented (including the pretarsus); with 1 movable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal.
The larvae non-aquatic (but found near water). The abdomen exhibiting functional abdominal spiracles. The larvae without gills. Abdominal tergum 8 without amature.
Worldwide and British representation. 1 species in Britain (L. pygmaeus). Recorded from scarce, South-west England and Wales and South-eastern England.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea; Limnichidae.
General comments on this taxon. A black beetle with yellow bases to the antennae and legs, convex below.
Miscellaneous. • Limnichus pygmaeus (from Joy). Limnichus pygmaeus (Limnichidae). Eubria palustris (Psephenidae). • Limnichus pygmaeus (with Dermestidae, Byrrhidae, etc.): Fowler 3, 97 (1889). • Fowler 3, 97 (1889): original legend..
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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: water beetles. Version: 18th September 2012. http://delta-intkey.com’.