What is the identify of the adjectives fresh marine aquarium crab?

I bought them (a couple) today for $2.49 in petsupermarket. Hope this helps you get the drift my question.
I don't reckon my fish have seriously...
Well, why didn't you ask when you bought them?
Whats wrong next to my goldfish?
shouldn't you enjoy asked then done heaps of research on it so you can take proper care of it first instead of buying it and later finding out.

other than that possibly a fiddler crab
these are often sold for freshwater but are actually brackish animals
I hold a 46 gallon aquarium and...
Answers:    fiddler crabs?

looks kinda like this?
http://www.nilesbio.com/images/categorie...

they are probably the most commonly sold FW crab in the US
What's wrong next to my betta fish?   Mystery snail crawling completely out of river?   African dwarf frog lend a hand and guppy support and shark cat give a hand?   I enjoy 4 unusual phirrannas and dont know what the reservoir should be at what can live near them and etc.?