Amarinus Laevis as far we know, to me a crab looks like a crab lol a mate of mine found them on the fresh water side of a local estuary in geelong australia, from what he told me there was quite a few of them, he grabbed a dozen or so and put them in a small tub pond with very very slight brackish water and then changed the brackish water out to fresh water over time, they now breed and behave just fine, i put 3 females in my community tank as a clean up crew, we have found tho that the males should only be added for breeding purposes as they tend to be super aggressive where the females are really laid back, if you can catch them in the open areas of the tank and be gentle they will crawl onto your hand but good luck hehe
To test the clean up capability of our tank:
Recently had my super old female beta pass on, we kept her in the 20L to live out her life -(My first and oldest fish) as we thought it would be best instead of putting the stress of a new tank onto her.
We put her dead body into our big tank at the front where there is a clear spot and we noticed a few things
The Crabs came in first and removed a lot of the bigger parts of flesh, within 2hrs most had been eaten
the shrimp closed in once the crabs had left they stayed for a while but were constantly startled by the corys-the shrimp ate most of what was left
the corys had a little peck but at most were disinterested
later that night all 4 apple snails were in that area and did not leave for several hours
the skeleton disappeared
during this time and before we added her body we did water tests every hour and surprisingly there was no increase which means the fish was eaten in a timely matter and that the amount and type of plants we have was enough to absorb the ammonia and other chemicals
been experimenting with creating a as complete as possible food cycle with the butterfly fish as the alpha predator the fighters as sub predators and the cherry & glass shrimp, siamese algae eaters, corys, crabs and snails as the clean up crew
we have found to that by regular feeding of live crickets and other pet grade insects that the butterfly fish is content not eating the fighters (for now)
that with regular flakes and blood worms shrimp loss has been minimal
that crabs like kicking fish in the face, seriously it hangs upside down from a leaf and waits till a fish gets close then it kicks a leg out and scares the crap out of the fish
the other good thing with the butterfly fish means that i can have a larger and more varied stocking of insects for my tarantula with out having to worry about the insects spoiling as the tarantula eats twice a week