Insects of Britain and Ireland: the families of Coleoptera

DELTA home

L. Watson and M. J. Dallwitz

Psephenidae

~ Dascillidaes. lat., Eubriidae-Eubriinae.

‘Water-pennies’, referring to the larvae.

General appearance. 1.5–2 mm long. Body length/maximum body width 1.35–1.77. Elytral length/pronotal length 2.8–4.57. Base of prothorax not or scarcely 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 oval; dorsally strongly convex; not necked; not waisted; black or dark brown. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Inclination of the head slight to strong. Eyes strongly protuberant; without bristles; finely facetted. The labrum concealed beneath the clypeus. Mandibles without a mola; without prosthecae. The mandibular apices simple. 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 somewhat expanded and truncate to subtriangular. The apical segment of the labial palps more or less expanded apically. Antennae long, but not exceeding the insect’s head to tail length; 11 segmented. Antennal scape not swollen. Antennae finely serrate.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.3–0.55. The pronotum with lateral keels (pronotal carinae); keels complete. Posterior edge of the pronotum distinctly crenulate. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly narrowly rounded or acute. The prosternal process complete; slightly overlapping the mesoventrite. Metaventrite with a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities open behind externally; broadly open; narrowly separated; strongly transverse; without lateral extensions; internally open. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less 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; in Eubria, not markedly extended laterally; posteriorly shaped to receive the retracted femur; with a steep transverse declivity against which the femur retracts. 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 with an appendage, or not appendaged; appendages when present, not or only lightly sclerotized. The claws of the mid-leg tarsi simple, or one-toothed or bifid. Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytral length/maximum width across the elytra 1.05–1.38. Elytra exposing no more than part of the terminal tergite; hard; non-glabrous (shortly, finely and densely hairy). Elytra with six or more impressed striae; the lines per elytron 6–7, or 8. Scutellary striole present (in the British representative, associated with a prominence near the scutellum). Wings well developed. Wings without an anal lobe. Wings with a medial fleck, or without a medial fleck; the medial fleck when present, not bisected by a vein. Abdominal sternites 5–6; comprising both fused and moveable components. Basal abdominal sternites immovably joined 3. Abdominal segment 8 apparently without functional spiracles. The male external genitalia trilobate.

Adult habitat, ecology. Water-beetles, or land-dwellers (? aquatic or sub-aquatic, being found in moist places and sometimes in water). Beetles 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 replenishing air for respiration beneath the elytra indirectly from that acquired and held in the ventral plastron; not noticeably posing regularly at the water surface to replenish air; incorporating bubbles of oxygen directly into the plastron. Not predacious; the rare British representative has been recorded on and under sticks in water courses.

Larvae. Mature larvae minute (less than 3 mm long). The larvae strongly flattened and disc-like; oblong to ovate. Body strongly flattened. Vestiture not restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented; more than 0.5 x the width of the head. Stemmata present; on either side of the larval head 6. The larval fronto-clypeus not extended forwardly. The frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth. The maxillary palps 3 segmented, or 4 segmented. The labium with a ligula at least as long as the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen extending to the underside. The abdomen with functional spiracles confined to the the eighth segment; with the spiracles on the eighth segment borne at the ends of spiracular tubes. The larvae with abdominal gills; with anal gill tufts. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae aquatic; found clinging to submerged wood and stones; phytophagous (on algae).

The disc-shaped ‘water penny’ larva is flattened and limpet-like, with head, legs and gills hidden from above by broad marginal extensions from all the segments.

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea.

Representation in Britain and Ireland, and worldwide. About 275 species worldwide; genera about 35. 1 species in Britain (E. palustris); genera in Britain 1; Eubria.

General comments. Oval to coin-shaped, often coppery beetles, with deeply furrowed elytra. The larva is truly aquatic, but the status of adult E. palustris as a ‘water beetle’ is unclear from the accounts seen..

Illustrations. • Eubria palustris: Fowler 4 (1890). • Eubria palustris (from Joy). Limnichus pygmaeus (Limnichidae). Eubria palustris (Psephenidae).


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’.

Contents