Amphizoa is a genus of aquatic beetles in the suborder Adephaga, placed in its own monogeneric family, Amphizoidae. There are five known species of Amphizoa, three in western North America and two in the eastern Palearctic. They are sometimes referred to by the common name troutstream beetles. The legs are not well adapted for swimming, and lack long swimming setae. The hind coxae extend to the lateral margin of the abdomen and the tarsal formula is 5-5-5.

thumb|right|100px|Genitalia: Amphizoa insolens

thumb|right|100px|Lateral view: Amphizoa insolens

thumb|right|100px|Ventral view: Amphizoa insolens

thumb|right|100px|Dorsal view: Amphizoa insolens

Known species of Amphizoa

The genus Amphizoa contains the following known species:

When disturbed, adults exude a yellowish fluid from the anus, with an odor described as that of cantaloupe or decaying wood, probably as a defense mechanism against predators like frogs and toads. An analysis based on a morphological character matrix also came to this conclusion. However, two other studies with more genes have placed Amphizoidae as sister group to Aspidytidae. With Aspidytidae and Amphizoa share the same morphology of the apical part of the pro-sternal process and the mesocoxal cavities. The phylogeny within Amphizoa has been analysed in two studies based on morphological characters and they suggested that A. davidis is an isolated species and sister to the remaining four species as follows (A davidis, (A. insolens, (A. striata, (A. sinica & A. lecontei)))).

References

  • Amphizoa insolens. California Beetles Project.

Further reading

  • Philips, K. T. and W. Xie. "Amphizoidae", in Arnett, R. H. and M. C. Thomas, American Beetles (CRC Press, 2001), vol. 1