Minimum Order is 5. Black Japanese Trapdoor Snails (Viviparis maleatus)TRAPDOOR SNAILS BIG SELLER. A pond isn't complete without adding algae eating pond snails. The trapdoor snails are black in color and range from 1" to 3" in size. Check out FAQS on our website for details on snails. When temps are 80 degrees and higher its a good idea to select two day transit to insure live delivery. Will not guarantee if weather is too warm. Please note: Minimum order is 5.