The art team created a number of lovely new icons for hunter pets in early MoP (or was it late Cata?) but they were never implemented. They're just sitting in the game database unused. These were for ones where the current icon either isn't the right beast at all (like basilisks and shale spiders) or is a beast with riding harness or something.
We've requested for them to be implemented a few times now, but nothing has ever come of it. Maybe WoD will finally be the time!
I've posted a reminder request here:
http://us.battle.net/wow/en/forum/topic/13086799039#1
UPDATE: Sorry, you need to be be flagged for the beta in order to post 
   If any of you have a moment to post in support it'd be much appreciated 
  No rush; if posts appear over a longer time period at least it'll be bumped now and then 
 Maybe someone will see it and care.
Thanks 
FYI, the icons are:
 

 Basilisk: inv_pet_basilisk
 

 Crane: inv_pet_crane
 

 Direhorn: inv_pet_direhorn
 

 Goat: inv_pet_goat
 

 Dog: inv_pet_mastiff
 

 Monkey: inv_pet_monkey
 

 Shale Spider: inv_pet_shalespider