Myxophaga
Myxophaga is the second-smallest suborder of the Coleoptera after Archostemata, consisting of roughly 65 species of small to minute beetles in four families. The members of this suborder are aquatic and semiaquatic, and feed on algae.
Myxophaga have several diagnostic features: the antennae are more or less distinctly clubbed with usually fewer than nine segments, mesocoxal cavities are open laterally and bordered by a mesepimeron and metanepisternum, the hind wings are rolled apically in the resting positions. Internally, they are characterised by the presence of six malpighian tubules and the testes are tube-like and coiled.[1]
Beetles of this suborder are adapted to feed on algae. Their mouthparts are characteristic in lacking galeae and having a mobile tooth on their left mandible.[2]
There are four extant families in the suborder Myxophaga divided between two superfamilies,[3] containing about 65 described species,[4] and at least one extinct family.[a]
Living members of Lepiceridae are confined to northern South America and Central America. Members of Sphaeriusidae occur on all continents except Antarctica, while Hydroscaphidae occurs on all continents except Australia and Antarctica. Torridincolidae occurs in Africa, Asia, and South America.[5]
Little about the fossil record of Myxophaga is known. Fossils from the early Late Cretaceous (Cenomanian) aged Burmese amber from Myanmar, have been assigned to the extant genus Lepicerus and extinct genus Lepiceratus within Lepiceridae,[6][7][8] as well as Burmasporum, which belongs to Sphaerusidae.[9] No impression fossils of myxophagan beetle were described until 2012, probably because of their small body size and specialized habitat.[10] A fossil specimen, assigned to the living genus Hydroscapha in Hydroscaphidae, was described in 2012 from the Yixian Formation in the Jehol Biota, dating from the Early Cretaceous (Aptian).[10] In 2019, Leehermania from the Late Triassic (Norian) Cow Branch Formation of North Carolina, which had previously been interpreted as the oldest known rove beetle was reinterpreted as an early diverging relative of the family Hydroscaphidae, making it the then oldest known Myxophagan.[11] In 2021, numerous specimens of a new myxophagan were described from a coprolite found in Late Triassic (Carnian) aged sediments in Poland. The new taxon Triamyxa, was placed in its own monotypic family Triamyxidae, and was resolved as either the most basal myxophagan or sister to Hydroscaphidae.[12]
