Insects of Britain and Ireland: the families of Coleoptera
= Dytiscidae part; including Phreatodytidae.
General appearance. 3.5–5 mm long. Body length/maximum body width 1.38–2.1. Elytral length/pronotal length 2.05–3.75. Base of prothorax not or scarcely narrower than the combined elytral bases, or distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width, or distinctly narrower than greatest elytral width. Beetles not necked; yellowish- or reddish-brown. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae. The underside without a plastron of hydrofuge hairs.
Detailed morphology. Inclination of the head slight. Eyes not strongly protuberant; without bristles; finely facetted. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles without a mola; with reduced prosthecae, or without 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 apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps more or less expanded apically. Antennae short; 11 segmented; more or less filiform (but somewhat thickened, the segments varying in shape and somewhat produced on the inner side and the fifth somewhat dilated in the male). Antennal insertions hidden from above; not in fossae.
Cervical sclerites absent. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.4–0.65. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax with notopleural sutures. Scutellum absent. The prosternal process complete; moderately or strongly overlapping the mesoventrite, or concealing most or all of the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in procoxal cavities. The fore-leg coxal cavities open behind externally; broadly open; quite widely separated; circular to longer than wide; without lateral extensions; broadly closed internally. The mid-leg coxae countersunk in mesocoxal cavities; separated by less than the shortest diameter of the cavity to more than the shortest diameter of the cavity. The mid-leg coxal cavities moderately to widely separated; not or scarcely oblique; open laterally. Hind-leg coxae contiguous or narrowly separated; much enlarged (and with characteristic, conspicuous inner longitudinal plates covering the articulations of the trochanters); extending laterally to meet the elytra; immoveably fixed to the metasternum and dividing the first abdominal sternite; constituting longitudinal plates that are fused to one another and joined with the metasternum, endowing the beetle ventrally with a flat, median longitudinal keel. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without hidden segments. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi equipped with swimming hairs; with as many segments as the mid-tarsi; 5-segmented; flattened and oar-like for swimming.
Elytral length/maximum width across the elytra 0.92–1.56. Elytra exposing no more than part of the terminal tergite; glossy. Elytra with six or more longitudinal lines of punctures, or apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae; the lines per elytron when more than five, 6–7, or 8. Scutellary striole absent. Wings well developed, or absent or much reduced. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 4–6; all articulated and moveable, or comprising both fused and moveable components. Basal abdominal sternites immovably joined when present, 2, or 3. Abdominal segment 8 with apparently functional spiracles. The male external genitalia adephagan.
Adult habitat, ecology. Water-beetles. Beetles free-swimming and diving strongly, with the main thrust delivered by the specially adapted hind legs, moving clumsily on land. Diving and Rowing by parallel-simultaneous leg movements. Beetles respiring under water via air which is collected posteriorly and stored directly under the elytra (respiring via the terminal pair of spiracles, cf. Dytiscidae); regularly posing tail first at the water surface to replenish air; collecting air at the water surface by exserting the tip of the abdomen through the surface film. Predacious, or not predacious (?).
Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae campodeiform; elongate and more or less parallel-sided. Body circular in cross-section, or somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 4 segmented; 0.15–0.5 x the head width. Stemmata present; on either side of the larval head 6. The larval fronto-clypeus not extended forwardly. The 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 3 segmented. The labium without ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 6 segmented; with 1 moveable claw. Visible abdominal segments 9. Tergum 9 of the abdomen completely ventral. The abdomen having functional spiracles on anterior segments (these annular), or with functional spiracles confined to the the eighth segment; without spiracular tubes. The larvae without abdominal gills. The abdominal apex without a respiratory chamber. Abdominal tergum 8 bearing a single median process with a pair of spiracles at its apex. The last abdominal segment with cerci.
Larvae aquatic; probably predacious (but not digesting extra-orally).
Classification. Suborder Adephaga; Superfamily Caraboidea.
Representation in Britain and Ireland, and worldwide. About 230 species worldwide; genera 12 (especially tropical). 2 species in Britain; genera in Britain 1; Noterus. E.g., N. clavicornis (Marsham's Noterus Water-beetle).
General comments. Beetles dorsally very convex and boat-shaped, the scutellum invisible; burrowing in ponds and marshes..
Illustrations. • Noterus clavicornis (Marsham's Water-beetle: B. Ent. 236). • Noterus clavicornis (details, B. Ent. 236). • Noterus clavicornis: B. Ent. 236, legend+text. • Noterus clavicornis: B. Ent. 236, text cont..
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. Insects of Britain and Ireland: the families of Coleoptera. Version: 16th May 2016. delta-intkey.com’.