Description

Adult Scirtids are mostly soft-bodied, elongate and flattened although several genera e.g. Scirtes and Ora include some rounded and convex, almost globular species. Some are continuous in outline e.g. Macrohelodes Blackburn, 1892 (Australia) and Amplectopus Sharp, 1886 (New Zealand), but most are constricted between the pronotum and the elytra e.g. Elodes and Microcara. The New Zealand genus Veronatus Sharp, 1878 is atypical; members are very elongate with several longitudinal carinae and various depressions to each elytron, and a cryptic silky appearance due to the pubescence which is arranged in patches lying in different directions. Most Scirtids are pubescent and some are very densely so e.g. Nipponocyphon, the pubescence is often doubled but the dorsal surface generally lacks any discreet longer sensory setae, some genera e.g. Cyphotelus Sharp, 1878 and Macrohelodes are virtually glabrous. The head is naturally declined, although easily raised forward for setting, and sometimes almost completely concealed under the pronotum; the temples are well-developed although usually concealed; in some genera e.g. Stenocyphon and Cyphotelus they are long and obvious beyond the pronotum. The eyes are entire or only very weakly emarginate anteriorly, flat to very convex and lacking setae. A transverse occipital ridge is sometimes present and, with the exception of Stenocyphon, all species lack a distinct frontoclypeal suture, the labrum is free, transverse and truncate to weakly emarginate although occasionally strongly so e.g. in Byrrhopsis Champion, 1913, Atopida White, 1846 and Cyphanus Sharp, 1878. All have paired lateroventral subgenal ridges which line up against the outer edges of the pro-coxae when the beetle is at rest. The mandibles are short, broad and rounded to a sharp point, although bidentate in e.g. Stenocyphon and Amplectopus, and variously toothed internally. The apical segment of the labial and maxillary palps is elongate- cylindrical to short and conical. Antennae 11-segmented and generally filiform although sometimes serrate, never clubbed, and placed on the front of the head where the insertions are visible from above, sometimes they are placed in well-defined depressions, and the separation varies from narrow to very wide. Ventral antennal grooves vary from strongly depressed to absent. The pronotum is generally transverse and convex, often widely explanate laterally, and with the sides straight to strongly rounded, broadest from the base to the middle and usually narrowed anteriorly; the apical and basal angles generally rounded, sometimes contributing to a continuous curve anteriorly and often bluntly acute posteriorly, the basal margin varies from straight to widely and strongly sinuate. A lateral border is usually complete and visible from above. The surface is generally smooth; in some there are paired basal fovea but never longitudinal impressions, the punctation varies from very fine and sparse to rather strong and dense, and the pubescence from recumbent to semi-erect. Prosternum narrow, and sometimes very much so, in front of narrowly separated and transverse coxal cavities which are open laterally, the process extending back and sometimes overlapping the mesoventrite, usually strongly constricted between the coxae and apically expanded to a rounded or widely truncate apex, flat or concave to strongly convex and projecting above the coxae which usually project above the level of the prosternum. Pro-trocantins generally narrow and visible from below, in Stenocyphon expanded and quadrate or nearly so. Scutellum usually large and obvious, triangular to rounded. Meso-coxae close together or touching, round to strongly transverse and not, or only very weakly, oblique, not projecting above the mesosternum, the cavities open laterally. Meta-coxae close together or touching, transverse and extending laterally to the elytral epipleura, posteriorly expanded into plates which are excavated to receive the femora, these plates are generally complete although sometimes weaker laterally and sometimes reduced e.g. in Scirtes, Ora, Cyphotelus and Stenocyphon etc. Most species have well-developed hind wings and are strong fliers. The elytra completely cover the abdomen and are generally rounded apically, usually with distinct or well-developed shoulders and broad epipleura that continue to the apex although these are occasionally reduced or even absent. The surface is usually punctured and pubescent, often with double pubescence, and lacking striae although in Veronatus there are several complete longitudinal carinae, and in Nipponocyphon there are numerous obscurely developed longitudinal striae. In some species, especially of Cyphon, the cuticle is folded into several weakly developed longitudinal ridges. The females of many species possess depressions or folds towards the apex of the elytra which have been termed ‘excitations’ as they secrete substances thought to be pheromones used to stimulate males during mating. The abdomen had 5 ventrites; segments 1 and 2 are connate and the basal segment lacks postcoxal lines although in Amplectopus Sharp, 1886, a genus of otherwise typical Scirtids from New Zealand, segments 1-3 are connate and there are distinct postcoxal lines. Most Scirtids have thin legs of moderate length; the femoral base is separate from the coxa and the femoral-trocanter joint is strongly oblique. In some the hind femora are rather well developed e.g. some Elodes, and in some e.g. Scirtes and Ora they are large and thickened, an adaptation for jumping as in alticine Chrysomelids, which has earned them the common name of marsh flea beetles. The tibiae vary from glabrous to densely pubescent and the outer margins have 2 longitudinal carinae which often bear series of stiff setae or spines. There are 2 tibial spurs which are generally short and equal or subequal but in some genera e.g. Stenocyphon, Ora and Scirtes, they are long and unequal. The tarsi are 5-segmentes, usually with the fourth segment bilobed or at least expanded although others may also be expanded, otherwise the segments are quadrate to weakly elongate, Scirtes and some others are unusual in having the basal metatarsomere long and thin. Exceptionally e.g. in Amplectopus the tarsi are short and broad.