Phylogeny and systematics of Sphaeriusidae (Coleoptera: Myxophaga): minute living fossils with underestimated past and present-day diversity
Sphaeriusidae (Coleoptera: Myxophaga) is a group of shiny, blackish and hemispherical riparian beetles, known for their miniaturized bodies. They are worldwide in distribution, but very limited information is available about taxonomic and morphological diversity, and natural and evolutionary history.
The presence of Bezesporum gen.nov. in Burmese amber and in recent fauna indicates that Sphaeriusidae largely maintained their specific morphology and specialized riparian lifestyle for at least 100 million years. Therefore, they can be considered an exceptionally conserved group, with a minimum of evolutionary changes over a long period. Our study also demonstrates that the species numbers and fine-scale morphological diversity of Sphaeriusidae are larger than expected in both the past and present-day faunas. Both were apparently underestimated due to the minute body size and cryptic habits of these beetles.
Suborder: MYXOPHAGA Crowson, 1955
Superfamily:SPHAERIUSOIDEA Erichson, 1845
Genus: Sphaerius Waltl, 1838
Species: S. acaroides Waltl, 1838
Size: 0.6-0.8mm
Around the World
This family contains a single genus, Sphaerius Waltl, 1838, in which there are around 23 species. They are all tiny, 0.5-1.2mm. and hemispherical in form. They are distributed throughout all the continents except Antarctica. Three species occur in the U.S.A and of the eight Palearctic species three are known from Europe. All species are aquatic or semi-aquatic occurring in a variety of damp habitats; mud, wet loamy soil and sandy or stony substrates. Some species store air beneath the elytra. In all species so far observed only a single egg is laid at a time. The larvae are broad and trilobite-like in form and live among detritus underwater. Only a single species, Sphaerius acaroides Waltl, 1838, is known from the U.K. It is widely distributed throughout Europe except for the Iberian peninsula and has recently been recorded from the Caucasus, Hungary and Romania.
| Major Group: Insecta Order: Coleoptera Family: Sphaeriusidae (formerly Microsporidae and Sphaeriidae) Genus: Sphaerius (formerly Microsporus) In Australia, this family contains a single aquatic genus, Sphaerius. |
| Descriptive Features: Adultsantennae with distinct 3-segmented clubbody shiny black, hemisphericalwings rolled apicallyabdomen with only 3 ventritestarsi 3-segmentedsize: minute, <1 mm Larvaeantennae 2-segmentedlabrum separated from head capsule by complete suturemandibular mola presentmaxillary palp 2-segmentedabdomen 9- or 10-segmentedabdominal spiracles 1-8 forming balloon-like tracheal gillsabdomen with a pair of small spiracular gills or tubercles on each of segments 1 – 8abdominal segment 9 with paired processes, unsegmented, immovablelegs 4-segmented with 1 clawsize: <2mm |
Ecology: Instream habitat: Sphaeriusid beetles are part of the interstitial fauna that lives in accumulations of gravel, sand and mud at the edges of streams and rivers
Feeding ecology: Adults are herbivores feeding on algae. Larvae are predators. However both adults and larva may also be scavengers feeding on detritus
Habit: Adult sphaeriusid beetles are minute and spherical. Larvae have eight pairs of balloon-like spiracular gills on the abdomen enabling them to breathe underwater.
A single species in Britain, Sphaerius acaroides Waltl. Approximately 0.6mm long, hemispherical and black, it looks very similar to a mite but walks like a beetle. Found mainly in moss adjoining small bodies of water, mainly in Dorset but records are relatively widespread. Historically regarded as scarce, but its small size and cryptic habits mean it is likely to be overlooked.
