The "Swamp Crayfish", Tenuibranchiurus glypticus, is listed by the Queensland Museum as the smallest freshwater crayfish in the world. I have been keeping these guys in aquariums since 2000 when I first collected specimens from a Tea Tree (Melaleuca) swamp that is part of the Noosa River System tributary system. These guys survive dry times and drought by burrowing deep down, all the way to the water table, and can be found living beneath areas that never actually go underwater, even during floods.
In the wild these guys live amongst the root systems of Tea Tree species. As the water table goes up and down, so do these guys, eating the various biota (fungi, worms, bacterial growths) that is associated with the wet soil around the root system.
During floods, the water table rises above ground level and these guys come out of the ground to find mates, move locations and also feed on the flush of nutrients and food associated with rain events.
in 2010, ten years after I started keeping them, these guys were listed on the IUCN Red List as endangered, this prohibits collection from the wild. Luckily I have maintained a captive population for close to twenty years.
At a maximum body length of around 2.5cm, this little crayfish is the perfect candidate for small aquariums, "nano-tanks", and can be easily bred in ten litres or less.