Sea lions have strong front flippers that they can use to walk on.  They are also capable of using their hind flippers for walking.  They have external ears.

Seals cannot use either their front or hind flippers for walking and must "scooch" across land on their bellies.  They also lack external ears.

There are two primary categories of whales, including toothed (Odontceti) and baleen (Mysticeti) whales. As the name implies, toothed whales differ from baleen whales in that they have teeth in their mouths. In addition, they tend to be predatory, feeding on fish, squid, and marine mammals. Most toothed whales are smaller than baleen whales, with the exception of the sperm whale; although, there is a pigmy sperm whale that is quite small. Perhaps the most familiar of toothed whales is the killer whale, or orca, famous for their antics at Sea World. Dolphins and porpoises are also included in this group.  Toothed whales have a single blow hole.

Baleen whales, on the other hand, have a mouth cavity filled with baleen, a series of plates that filter sea water and capture small food items, such as the tiny krill (a shrimp) and other planktonic organisms. Baleen whales include the blue whale, the humpback whale, and the grey whale, to name a few. Baleen whales have two blow holes.