
Congrats on the new crayfish. js has given you some sound advice here-especially a lid.

As much as I like those guys,I wouldn't want them parading around the house,although my cat's would love it.
Depending on the size of the crayfish,they normally tell you to allow about 10 gals. per each.I've seen smaller ones kept in groups,but I think they get a bit territorial as they get bigger.
I found this site which may help.Good luck and do post pics.
http://crayfish.byu.edu/faq.htm