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.
Description
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]
Taxonomy
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.[10]
Fossil record
The fossil record of myxophagan beetles is sparse, likely due to their small size limiting
preservation potential.[5] The currently oldest myxophagan is Triamyxa, described in 2021 from numerous specimens of found in a
coprolite found in Late Triassic (
Carnian) aged sediments in Poland. It was placed in its own monotypic family Triamyxidae, and was resolved as either the most basal myxophagan or sister to Hydroscaphidae.[9] The next oldest is Leehermania from the Late Triassic (
Norian)
Cow Branch Formation of North Carolina, which had previously been interpreted as the oldest known
rove beetle but in 2019 was reinterpreted as an early diverging relative of the family Hydroscaphidae.[5] A fossil impression assigned to the living genus Hydroscapha in Hydroscaphidae is known from the
Yixian Formation in the
Jehol Biota, dating from the
Early Cretaceous (
Aptian).[11] 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,[12][13][14] as well as the extant Sphaerius and Bezesporum and the extinct Burmasporum and Crowsonaerius, belonging to Sphaerusidae.[7][8][6]
Gallery
Specimen of Sphaerius minutus (Sphaeriusidae) in various views
^Beutel, R.; Leschen, R. (2005). "Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim)". Band 4 Part 38: Arthropoda, Hälfte: Insecta, Coleoptera, Beetles. Handbuch der Zoologie/Handbook of Zoology. Vol. 1.
Walter de Gruyter.
ISBN3-11-017130-9.
^Cai, C.; Short, A. E. Z.; Huang, D. (2012). "The First Skiff Beetle (Coleoptera: Myxophaga: Hydroscaphidae) from Early Cretaceous Jehol Biota". Journal of Paleontology. 86 (1): 116–9.
Bibcode:
2012JPal...86..116C.
doi:
10.1666/11-050.1.
S2CID140170420.
^Kirejtshuk, A. G.; Poinar, G. (2006). "Haplochelidae, a new family of cretaceous beetles (Coleoptera: Myxophaga) from Burmese amber". Proceedings of the Entomological Society of Washington. 108: 155–164.
^Jałoszyński, Paweł; Luo, Xiao-Zhu; Hammel, Jörg U.; Yamamoto, Shûhei & Beutel, Rolf G. (2020). "The mid-Cretaceous †Lepiceratus gen. nov. and the evolution of the relict beetle family Lepiceridae (Insecta: Coleoptera: Myxophaga)". Journal of Systematic Palaeontology. 18 (13).
doi:
10.1080/14772019.2020.1747561