Family PSEPHENIDAE

Museums

Museum list

Regional Maps

Family PSEPHENIDAE

Compiler and date details

1 December 1999 - Andrew A. Calder, CSIRO Entomology, Canberra, Australian Capital Territory, Australia

Introduction

The Psephenidae is a small family represented in Australia by the genus Sclerocyphon Blackburn and 13 described species although a number of undescribed species are known from larvae (Davis 1986). The family contains about 29 genera and 210 species worldwide arranged in four subfamilies: Psepheninae, Eubrianacinae, Psephenoidinae and Eubriinae (Brown 1981; Lee & Jäch 1995; recent literature). The Psephenidae are represented in Australia by a single subfamily Eubriinae (Davis 1986) that has previously been treated as a separate family by some authors (viz. Bertrand 1972). Psephenidae occur in Europe, North America, South America, Africa, India, South-east Asia, Japan and Australia (Davis 1986). The larvae, commonly called water pennies, are aquatic and are characteristically flattened and discoid in shape. They are a distinctive component of the benthic invertebrate fauna and are fairly common in rocky rivers, streams and lakes of eastern Australia and Tasmania although Sclerocyphon fuscus Bertrand & Watts has been recorded from permanent water in the George Gill Ranges of Central Australia (Davis 1986; Lawrence & Britton 1994). Brown (1981) considers that the presence of dryopoid beetles in streams throughout the year and their sensitivity to water quality changes confer on them great potential as ecological indicators in environmental studies. The difficulty of associating the larvae with adults on which the taxonomy of the group is based, has led to a taxonomic impediment and is of little use to freshwater ecological studies when large proportions of benthic communities consist of immature stages of aquatic insects (Wiggins 1966). This in turn leads to a situation where their potential as ecological indicators in environmental studies is not fully realised (Davis 1986).

The first Australian psephenid was described by Fabricius (1775) as Tritoma collaris. Blackburn (1892) described a second species and a further four species were described by Lea (1895, 1919). Carter (1935) decribed another two species both of which turned out to be synonyms and Pic (1924) added another species and subspecies both of which are synonyms of Sclerocyphon maculatus Blackburn. Bertrand & Watts (1965) inadvertantly described the new species Sclerocyphon fuscus from larvae collected in the Adelaide region in their monograph of the biology, larval and pupal stages of Sclerocyphon. Smith (1981) described the larva, pupa and adult of two Tasmanian Sclerocyphon species as well as describing the life history of S. secretus Smith. Davis (1986) then revised the entire genus, described another five new species describing the male, female and last-instar larva of most species except for S. serratus Lea, S. collaris (Fabricius), S. aquilonius Davis and S. nitidus Davis. Another five larval types that had not been associated with adults were also described.

Most of the biological information recorded for the Australian species is due to Bertrand & Watts (1965) and more recently by Smith (1981) and Davis (1986). The larval stage is entirely aquatic being present in streams and rivers throughout the year while the adult and pupal stages are terrestrial, cryptic and shortlived for a few weeks in spring and summer. Larval Sclerocyphon cling to rocks in streams and rivers where they feed upon attached algae. The larvae are negatively phototropic and during daylight hours cling to the underside of stones in streams. In dim light and at night they move to the upper surfaces to graze upon attached algae. Smith & Dartnall (1980) have studied the hydrodynamics of larval Sclerocyphon and hypothesised that the streamlined form of the larvae enable larvae to move across rocks in fast flowing streams enabling them to exploit resources unavailable to their benthic competitors. Last instar larvae leave the water and remain hidden on the stream bank for several weeks before pupating. Only last-instar larvae possesses functional spiracles (Hinton 1955) which are covered by a pair of brushes. Larvae have a prepupal phase and pupate within the last larval skin. Pupae then crawl a short distance free of the larval exuviae with the pupal stage lasting from 2 to 3 weeks.The pupae possess functional spiracles which open on the apices of very short conical tubercles on abdominal segments 2-7 (Hinton 1966). Adults usually remain hidden in litter, high-water leaf packs or debris on stream banks although they can be found resting on riparian vegetation and occasionally on hot sunny days they have been observed in flight above streams. The adults mate in the litter and females return to the water to lay eggs that are deposited in a single layer on submerged stones.

Diagnosis

Psephenid adults are broadly oval, flattened beetles clothed with a fine, short, dense pubescence that forms a pattern. Adults range from 3.2–7.7 mm in length. The head is deflexed, narrowed to form a short rostrum and is partially visible from above. The antennae are 11-segmented and filiform or serrate. A fronto-clypeal suture is absent. The mouthparts are concealed by a prosternal chin-piece. The mandibles and maxillae are reduced and the maxillary palps are truncate or securiform apically. The pronotum is transverse, with the anterior edge abruptly and deeply emarginate. The bases of the pronotum, scutellum and elytra are finely crenulate, forming an interlocking device. The procoxae are transverse with exposed trochantins and the procoxal cavities are open behind both internally and externally. A narrow to moderately wide prosternal process is present and fits into a mesosternal cavity. The mesocoxae are narrowly to widely separated while the metacoxae are approximate. The metasternum has a distinct transverse suture. The hindwing has an obliquely closed radial cell and no anal (wedge) cell. The tarsi are 5-segmented, long and simple. The claws are simple and without a tooth (Lawrence 1982; Davis 1986).

The larvae are broadly oval, strongly flattened and disc-like with the head and legs concealed from above. The last larval instar ranges in length from 3.9–10.2 mm. The thoracic-abdominal disc is clothed with granules and modified setae and is lined with a marginal fringe of setae. The dorsal surface has 2-4 pairs of defensive gin traps. The head has a cluster of five or six stemmata on each side and the epicranial stem is short. The antennae are moderately long and three-segmented. The mandibles have a simple scooplike apex and prostheca. The labrum is large and the maxillae are freely movable but are partly concealed behind an expanded postmentum. Functional spiracles are present on segment 8 in the final instar only or are absent. A spiracular brush on tergite 9 opposite each spiracle prevents the opening from being clogged with silt. Sternite 9 has a movable operculum, concealing a chamber which houses paired retractile gills. Urogomphi absent (Lawrence 1982; Davis 1986; Lawrence & Britton 1994).