CONGRATS TRIATHLETE!!
Great job! And good on you for swimming in water w/ jellyfish! YIKES! Thats the one reason why I'll NEVER do Ironman Florida.
As for the run... As Nanci said- bricks. But your legs will always feel a bit wierd and gumby like off the bike. In a race situation you tend to give it your all and when you hit the run your legs will let you know! Also did you do the ride on a mtn. bike? If so that could also be part of the reason. The effort from riding the mtn bike prolly took alot out of your legs.
Well CONGRATS again! Great job!