Question: Do all animals have white blood cells?

Kevin Mahon answered on 19 Jun 2012:

No they don’t – many invertebrates for example have cells that perform similar fucntions called coelomocytes instead. They are found in arthopods, starfish and many of the worms. They function in a similar manner but are distinct. Many scientists theorise that these invertebrate immune systems are actually a precursor to the systems we see in most animals.