British insects: the families of Coleoptera


L. Watson and M. J. Dallwitz

Pomatinus Sturm

Adults. Beetles sub-aquatic to aquatic (under submerged logs and stones in rivers); 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; presumably replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron; incorporating bubbles of oxygen directly into the plastron (?). Beetles 4.5–5.5 mm long; body length/maximum body width 1.7–3.2; 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. Beetles without ventral body cavities for reception of the legs; not necked. Upper surfaces of body non-glabrous. Beetles with very short, appressed pubescence throughout. Upper surfaces of body with neither scales nor scale-like setae. Inclination of the head slight to strong.

Eyes two; strongly protuberant, or not strongly protuberant; bristly, or without bristles. Mandibles with a well developed mola. The maxillae with distinct galea and lacinia apically to the palp; without stylet-like lobes. The maxillary palps not especially elongated. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae very short, or short; not strongly asymmetric. Antennal scape not swollen. Antennae clubbed, or pectinate. Antennal clubs 6–10 segmented (‘six or more’). Antennal insertions visible from above, or hidden from above; not in fossae.

Prothorax without notopleural sutures. Pronotal length/maximum pronotal width 0.4–1.05. The pronotum without a short longitudinal furrow on each side (less contracted anteriorly than in Dryops). 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; not shaped posteriorly to receive the 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; without an associated empodium. Hind tarsi with at least as many segments as the mid-tarsi; 5-segmented. Hind tarsi without ‘swimming’ hairs.

Elytral length/maximum width across the elytra 1.1–2.3. Elytra exposing no more than part of the terminal tergite; hard. Scutellary striole absent. Elytra non-glabrous (covered with fine, appressed hairs). Exposed abdominal sternites 5; comprising both fused and movable components; immovably joined 2. Abdominal segment 8 with apparently functional spiracles.

Adults not predacious; close to fresh water. Under submerged logs and stones.

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 3 segmented; less than 0.15 x the with of the head, or 0.15–0.5 x the head width. Stemmata 6. Frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles 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 aquatic to non-aquatic. The abdomen having functional spiracles on anterior segments. The larvae without gills. Abdominal tergum 8 without amature. The larvae not predacious; consuming decaying plant material and consuming rotting wood (in wet soil and leaf litter, and waterlogged wood).

Worldwide and British representation. 1 species in Britain (P. substriatus). Recorded from Northern England, South-west England and Wales, and South-eastern England.

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Dryopoidea; Dryopidae.

Miscellaneous. • Parnus auriculatus and Pomatinus, with Elmidae and Heteroceridae: Fowler 3, 98 (1889). • Fowler 3, 98 (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.’.