Plankton is not the name of a plant or animal but more of a category for any drifting organism that inhabits the middle to upper levels of the ocean, namely the pelagic zone.
Most vets do spays, neuters, bone surgeries, spleen surgery, tumor removals, and intestinal surgeries. Heart surgery and more complicated surgeries are done by specialists that requires more schooling. If you want to be a vet, you have to have REALLY good grades and Vet school is MUCH harder to get into than human medical school.
Many vets specialize in treating household pets. Veterinarians may visit schools as part of a community outreach program. A veterinarian might get training with exotic pets, like guinea pigs. A veterinarian may specialize in large animals, which often includes farm animals like horses, cattle, and sheep. Exotic animal vets might tend to giraffes at zoos. Some veterinarians choose to specialize in horse care. Hamsters are cared for by small animal veterinarians.