Horseshoe crabs?

[Salmon King]

You need a fairly big tank but not 10000 gal.The only thing you pretty well have to have just sand and tiny bit rock.I put them in my 235 and all was well till they started bumping into things and turning over.The fish thought they were food .Scooped them out and took them back were I bought them.Seen marine bioligests keep them in not to big of tanks.You should do a little research before buying.