Amphizoa
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 eastern palearctic. They are sometimes referred to by the common name troutstream beetles. Description. Troutstream beetles have a characteristic appearance. They are relatively large, oval, slightly convex, dull black to piceus. Body length ranges between . The head is broad with a quadrate shape and small round eyes. The antenna is filiform, rather short with 11 segments. The pronotum is significantly narrower than the elytra and with  lateral margins slightly crenulated; the prosternal processes are broad and flat, rounded to truncate at the apex; the elytra are vaguely striate and have a series of short spines of unknown function. 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. Known species of "Amphizoa". The genus "Amphizoa" contains the following known species: Biology. Troutstream beetles can be found in streams and rivers in mountain regions of China, North Korea and western North America. Streams are often  cold and medium to fast flowing, and the beetles can be found clinging to rocks, woody debris or at margins. Both adults and larvae are predators, especially on stonefly larvae but occasionally on other aquatic insects. Larvae may also scavenge dead insects. 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. Phylogeny and evolution. Amphizoidae share some plesiomorphic features with Carabidae, such as slender ambulatory legs, and other characteristics with Dytiscidae, such as large sensorial lobes on  the epipharynx. In an analysis based on the genes 18S rRNA, 16S rRNA and cytochrome oxidase I, Amphizoidae was placed as a sister group of a clade comprising the newly described family Aspidytidae, Paelobiidae(=Hygrobiidae) and Dysticidae. 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")))).