PSEPHENIDAE Lacordaire, 1854
Water Penny Beetles
Represented by a single species in the UK. Eubria palustris is a small beetle which is widespread but local in wetland situations.
Introduction
This is a small family of about 300 species in 38 genera and 5 subfamilies. The group is generally cosmopolitan although missing from many islands including New Zealand, diversity is greatest by far in tropical regions and they are usually only poorly represented in temperate areas; 16 species of several genera occur in the Nearctic zone while 13 species of the single genus Sclerocyphon Blackburn, 1892 (Eubriinae) occur in Australia and only the single Western Palaearctic Eubria palustris Germar, 1818 occurs in Europe including the U.K. but not Ireland. Most genera, as well as some higher groups, tend to be restricted to a single region and there seems to be little overlap between Old World and New World groups. The following is a brief look at the subfamilies and some selected genera.
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The recently erected Afroeubrinae Lee, Satô, Shepard & Jäch, 2007 is monogeneric and includes 3 species of Afroeubria Villiers, 1961 from Ethiopia.
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Psephenoidinae Hinton, 1939 includes 7 genera and about 25 species from the Palaearctic, African and (mostly) Oriental regions. Afropsephenoides Basilewsky, 1959 includes 3 species from South Africa and the Congo. Psephenoides Gahun, 1914 is the largest genus with 11 species from Southeast Asia. Heteropsephenoides Horaki, Jang & Jäch, 2003 includes a single Southeast Asian species.
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Eubriinae Lacordaire, 1857 with 16 genera and about 180 species is the largest subfamily, members occur throughout the world but the greatest diversity is in Southeast Asia. Eubria Germar, 1818 includes 3 species from Europe and Asia including North Korea. The Nearctic Acneus Horn, 1880 includes 4 species, and Microeubria Lee & Yang, 1994 includes about 12 species from southern Asia (India & Nepal) and Southeast Asia including Laos and Borneo. Ectopria LeConte, 1853 includes 21 species from Southeast Asia and 2 from North America. The large genus Dicranopselaphus Guérin-Méneville, 1861, with about 40 species is, unusually, almost Holarctic.
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Psepheninae Lacordaire, 1854 with 8 genera and more than 60 species is mostly Neotropical although Metaeopsephus Waterhouse, 1876 includes 15 Palaearctic and African (Guinea) species. Phenops Darlington, 1936 is Neotropical with 11 species while Psephenus Haldeman, 1853 includes 18 species from across the Americas.
POLYPHAGA Emery, 1886
BYRRHOIDEA Latreille, 1804
Eubria Germar, 1818
E. palustris Germar, 1818
2-2.6mm
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Eubrianacinae Jacobson, 1913 with 6 genera and about 80 species is mostly Oriental or Southeast Asian but the 8 species of Afrobrianax Lee, Philips & Yang, 2003 are Ethiopian, while a single species, E. edwardsi LeConte, 1874, of the large genus Eubrianax Kiesenwetter, 1874 (>40 spp.) is Nearctic.
Ecology
The common name refers to the unusual aquatic larvae which might easily be mistaken for crustaceans; they have widely expanded dorsal sclerites and are often brown or coppery. The larvae are small, 3-10mm and strongly dorso-ventrally flattened, often oblong but sometimes almost round, with the head and appendages concealed by the thoracic and abdominal plates. In some the abdominal apex has a ventrally articulated operculum concealing 3 extrusible tufts of fine gills, in others the larvae have both paired abdominal gills and functional spiracles, thus they can breathe dissolved oxygen when submerged, but they can also respire when they leave the water to pupate. Species of Psephenoides are more fully adapted to an aquatic life as neither larvae nor pupae have functional spiracles and both have gills. Larvae have short 5-segmented legs with sharp claws adapted to clinging to rocks and stones in fast moving or turbulent water, and which are variously modified as scrapers, and their well-sclerotized chewing mouthparts are adapted for scraping algae etc. from submerged surfaces. They feed on periphyton, the thin layer of algae and micro-organisms that form on submerged rocks etc. but they are also thought to consume organic debris, and they seem to avoid surfaces with a thick organic layer. They are photophobic, avoiding light by clinging to the under surface of submerged rocks and stones etc. and are generally absent from loosely-packed, large-grained sediments, sands or substrates with a high organic or silt content. Larvae of many species are solitary but a few live in groups, they generally avoid still water and will move into water currents as they form, and their presence is an indicator of good water quality. All adults and most pupae breathe air but are rarely found away from the water edge. Adults are usually riparian occurring on rocks and stones or among partly-submerged overhanging vegetation or marginal leaf-litter and some e.g. species of Ectopria, are nocturnal, remaining cryptic and hidden during the day. They are short-lived, generally up to three weeks, they seldom feed and most have a short season, often early in the year, in temperate regions they are thought to be univoltine although the length of the life cycle may vary with latitude e.g. in Australia some Sclerocyphon spp. develop within 12 months in Queensland while in Tasmania they take 24 months, and temperature seems to be the most important factor. The biology of very few has been studied but so far as is known all are dioecious and fertilization is internal. Females oviposit in the spring after a period of feeding, often the eggs are laid above the water edge or on marginal vegetation and the emerging larvae crawl or drop into the water, but in some species the female enters the water and lays them on submerged stones etc., sometimes remaining submerged for days and respiring via air trapped among the pubescent body surface. Females of the Nearctic Psephenus herricki (DeKay, 1844) deposits hundreds or thousands of tiny, bright yellow eggs on submerged and emergent objects in fast stream currents. Larvae develop through the summer, passing through several larval instars, in Sclerocyphon 5 or 6, and overwinter under stones or among debris. Fully grown larvae usually leave the water to pupate among the marginal substrate, they construct a pupal cell and pupate inside the final larvae skin, although some species construct an air-filled pupal cell under water and species of Psephenoides may pupate among aquatic vegetation etc. In some Sclerocyphon the pupae occur in clusters and this stage lasts about 3 weeks. The adults of most psephenids are diurnal, occurring on marginal vegetation or rocks etc. exposed above the water, in the spring they may become very active and swarm as they look for mates, the nocturnal Ectopria are sometimes attracted to light in large numbers. Many species are collected by beating marginal vegetation or simply by searching likely host material.
Description
1.5-8mm. Elongate to broadly oval and often continuous in outline, sometimes continuously curved overall e.g. Sclerocyphon Blackburn, 1892, and moderately convex to strongly flattened. Dorsally smooth or with only shallow depressions or weakly raised longitudinal elytral carinae. Mostly drab coloured, testaceous to red or black but sometimes bicoloured or patterned e.g. Acneus quadrimaculatus Horn, 1880. Upper surface pubescent, this may be dense and coloured so producing a striking pattern, or very fine and inconspicuous e.g. in Eubria or Ectopria, but without erect setae, ventrally often pubescent but without hydrofuge surfaces. Head quadrate and partly retracted into the thorax, usually with convex, prominent eyes and lacking temples, generally horizontal or weakly declined, flat to gently convex and without impressions. Eyes finely faceted and glabrous; entire or, rarely, weakly emarginate anteriorly. Frontoclypeal suture absent or weak and incomplete, clypeus often produced forward; laterally smooth, anterior margin smoothly rounded to weakly emarginate. Labrum transverse and at least partly exposed, apex truncate to gently emarginate, generally covering the short and broad mandibles. Apical palpomeres cylindrical to fusiform, without a mola or internal teeth and simply pointed, truncate, bi- or tri-dentate apically. Antennal insertions visible from above and moderately to widely separated, rarely close or even contiguous. Antennae 11-segmented and moderately long, rarely reaching the elytral apex, filiform to serrate, pectinate, plumose or clavate, often very well-developed e.g. Schinostethus Waterhouse, 1880, Acneus Horn, 1880 or Eubrianax Kiesenwetter, 1874, generally to some extent pubescent, never clubbed, the basal segment(s) rarely expanded. Pronotum very variable, transverse and broadest at or just in front of the base, lateral margins bordered throughout and evenly curved to rounded or produced anterior angles. Posterior angles variable; acute to perpendicular or widely rounded, basal margin almost straight to strongly sinuate and produced backwards medially. Surface evenly convex, without deep impressions, callosities or tubercles although sometimes weakly impressed either side in front of the base, without a median longitudinal impression. Prosternum variable but generally short and convex anterior to the coxal cavities, sometimes produced anteriorly into a distinct mentum, and lacking antennal cavities or grooves. Prosternal process variously developed, often extending to the Mesoventrite and sometimes overlapping the anterior margin, apex very variable from sharply acute to broadly rounded or truncate. Pro-coxal cavities transverse, often strongly so, and open externally, contiguous to widely separated. Scutellum very variable; usually large and well-developed, apically acute to rounded or truncate. Meso-coxal cavities round to weakly transverse, narrowly to moderately widely separated and open externally. Meta-ventrite flat to weakly convex, longer than the first abdominal ventrite, with a distinct transverse groove and sometimes with post-coxal lines. Meta-coxae contiguous or nearly so; transverse and horizontal but generally not reaching the elytral margin. Meta-coxae not enlarged but variously developed into plates which may partly cover the first abdominal ventrite. Elytra quadrate to elongate, up to 4.5X the pronotal length, continuously or separately rounded apically and completely covering the abdomen. Soft, lightly sclerotized and smooth, finely and sparsely to densely punctured, sometimes striate, the striae consist of variously developed rows of punctures which are rarely impressed, the number varies from a few to 8, without a scutellary row or a deeply impressed sutural stria, sometimes with weakly raised longitudinal carinae. Shoulders smoothly convex and not prominent, lateral margin straight or weakly sinuate and with generally poorly developed epipleura, sometimes missing, rarely wide or continued to the apex. Smoothly convex apically, not deflexed, and variously explanate, sometimes widely so e.g. in Ectopria LeConte, 1853. Hind wings well-developed, with normal transverse folds and lacking a fringe of hairs. Abdomen with 5-7 ventrites, the 3 basal ventrites connate, the fourth articulated or connate with the third. First ventrite not completely divided by the metacoxae, slightly longer than the second and lacking postcoxal lines. Legs proportionally short and thin, all femora of similar width, tibiae slender and not expanded apically, sometimes curved, the outer edges without ridges or spines, apical spurs generally missing. Tarsi 5-segmented; all segments cylindrical or nearly so, and lacking lobes, the basal and apical tarsomeres not appreciably longer than the intermediate segments. Claws paired and equal in length, without basal lobes, teeth or setae, and single, toothed or notched apically. Species often resemble scirtids but lack the bilobed fourth tarsomere seen in that family.
Eubria palustris Germar, 1818
This is the only member of the family to occur in Central Europe; it is widespread though sporadic and generally rare from Spain to Western Siberia and from Italy north to Southern Scandinavia and the UK. Here it is a very local and generally scarce species of England and Wales, including Anglesey though it may be common where found. Through much of its range it has declined in recent decades and is now considered threatened in several countries although because of its very distinctive appearance, both as adults and larvae, it seems unlikely the species would have escaped being recorded and historically it seems never to have been common. On the continent it occurs from lowland to low mountain altitudes, around 1700m, and is often most common beside fast-moving streams and springs in foothill situations. More generally it inhabits margins of ponds and streams, sometimes in forest situations, floodplain meadows, peat bogs and fens with permanently wet and sparsely vegetated areas exposed to the sun. Adults occur during June and July and may be observed among mosses or on waterside vegetation and rocks etc. are short-lived, do not feed and generally occur in numbers. Larvae develop through the summer from eggs laid in June or July; they overwinter under debris or in the soil out of water and pupate in the spring. They have tuft-like anal gills and are able to remain under submerged stones or among waterlogged moss etc. where they feed on algae, mostly diatoms. In upland situations they occur in fast-moving water with high calcium content and across much of Europe are typical of the fauna of upper parts of streams and springs. The larvae are distinctive; strongly flattened and disc-shaped with the head, appendages and gills hidden from above by laterally expanded body segments, the rounded shape and dull-brown or bronze colour has given rise to the common name.
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Adults are small, 2-2.6mm, and continuously rounded in outline, entirely shiny brown to very dark brown, sometimes with a metallic reflection, and very finely pubescent. From above the head is transverse with large convex eyes that occupy the entire side of the head, 11-segmented and filiform or weakly serrate antennae with the second segment globular and much shorter than 1 or 3, and short pale palps with the terminal segment weakly expanded towards the apex. Pronotum broadest at acute posterior angles and strongly narrowed to a rounded anterior margin, the surface evenly convex and with a pair of variable basal fovea. Scutellum large and triangular. Elytra smoothly and continuously rounded and completely covering the abdomen, with strongly impressed and weakly punctured striae; sutural stria curved under the scutellum and abbreviated in the basal third, the second incomplete, from the basal fifth to before the apex, the third and fourth united before the base and either united or separate before the apex, a fifth stria delimits the weakly explanate lateral margin in the apical half. Legs long and slender, tarsi 5-5-5 without modified segments, claws slender and weakly toothed at the base.
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