British insects: the families of Coleoptera
Including Cyphonidae, Elodidae, Helodidae.
Water-nymph beetles, Marsh beetles.
Adults. Beetles seemingly always terrestrial (though associated with helophytic vegetation in marshy places); walking in water or free-swimming by conventional ambulatory motion of the legs, not diving strongly. Beetles 1.5–5.5 mm long; body length/maximum body width 1–2.62; elytral length/pronotal length 3.14–8.2; 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 oval to elongate-oval; dorsally somewhat convex to dorsally strongly convex; not necked; somewhat waisted; yellow-brown. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae. Inclination of the head slight.
Eyes strongly protuberant, or not strongly protuberant; without bristles. Mandibles present, or absent or vestigial; when present, with a well developed mola, or with a reduced mola, or without a mola. The mandibular apices simple. The incisor edges of the mandibles simple, or with a single tooth, or with two or more teeth. 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 not expanded apically. Antennae short to about half the insect's head to tail length; 11 segmented. Antennal scape swollen. Antennae filiform (flattened). Antennal insertions visible from above; countersunk within saucer-like fossae, or not in fossae.
Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.22–0.83. The scutellum elevated, or not elevated. Metaventrite with a transverse groove, or without a transverse groove. The fore-leg coxal cavities broadly open; narrowly separated; strongly transverse; without lateral extensions; internally open. Hind coxae posteriorly shaped to receive the retracted femur (transversely excavated). Tarsal segmentation formula 5, 5, 5. Some of the tarsi exhibiting conspicuously bilobed segments (segment 4 only). 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; without an associated empodium. Hind tarsi with at least as many segments as the mid-tarsi; 5-segmented.
Elytral length/maximum width across the elytra 0.85–2.1. Elytra exposing no more than part of the terminal tergite; soft (and hairy). Scutellary striole absent. Wings well developed. Exposed abdominal sternites 5; all articulated and movable, or comprising both fused and movable components; immovably joined 2, or 3. Abdominal segment 8 apparently without functional spiracles.
Adults in damp places.
Larvae. The larvae campodeiform; elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; dorsally heavily pigmented or sclerotized; more or less heavily pigmented. The antennae 5–10 segmented (five or more); more than 0.5 x the width of the head. Stemmata fewer than 6 (one, two, or three). Frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule separated by a complete suture. 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 5 segmented (including the pretarsus); with 1 movable claw. Visible abdominal segments 8, or 9. Tergum 9 of the abdomen entirely dorsal.
The larvae aquatic. The abdomen exhibiting functional abdominal spiracles; with functional spiracles confined to the the eighth segment. The larvae with anal gill tufts. The abdominal apex with a respiratory chamber, formed from the 8th and 9th terga and enclosing a pair of enlarged spiracles. Abdominal tergum 8 without amature. The larvae phytophagous (on water plants).
The campodeiform larvae with anal gills; unique among those of Endopterygotes in having long, multi-segmented antennae.
Worldwide and British representation. About 1400 species worldwide; genera about 50. 16 species in Britain; genera in Britain 6; Cyphon, Elodes, Hydrocyphon, Microcara, Prionocyphon, Scirtes.
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Eucinetoidea. E.g., Hydrocyphon deflexicollis.
General comments on this taxon. Beetles of marshy places, with yellow legs and elytra that are soft and hairy, often with readily disarticulating limbs.
Miscellaneous. • Hydrocyphon deflexicollis: B. Ent. 602. • Hydrocyphon deflexicollis: B. Ent. 602, legend+text. • Hydrocyphon deflexicollis: B. Ent. 602, text cont.. • Microcara, Cyphon, Prionocyphon, Hydrocyphon, Scirtes (with Psephenidae and Lycidae): Fowler 4, 110 (1890). • Fowler 4, 110 (1890): original legend.. • Elodes marginata and E. minuta (with Elateridae and Dascillidae): Fowler 4, 109 (1890). • Fowler 4, 109 (1890): original legend.. • Hydrocyphon deflexicollis (Janson 188).
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’.