Baleen whales are larger than the toothed whales and have two blow holes. Female baleen whales are larger than the males. Many baleen whales are endangered from over-hunting. Baleen whales have baleen plates instead of teeth, which they use to filter food. Baleen is a sieve-like device made of keratin (the same substance that fingernails and hair are made of). Baleen is a series of stiff, flexible material that hang from the upper jaw. The inside of the baleen is edged with hairy plates that filter krill (tiny crustaceans), plankton (small animals and plants that float with ocean currents), and small fish. They feed simply by opening the mouth to fill it with krill-laden water, they then close it. Many baleen whale species migrate seasonally from cold-water feeding grounds to warm water breeding grounds. Many species congregate in groups called pods. Many species sing songs but they lack echolocation capabilities. Baleen whales have symmetrical skulls.

Gulpers or Swallowers:
These are whales that alternatively swim then gulp a mouthful of plankton or fish. Concentrated massses of prey are preferrable for this method of feeding. Gulpers include most rorquals, blue whales, pygmy blue whales, fin whales, Bryde's whales, humpback whales, and minke whales.
Skimmers:
These whales keep their mouths open most of the time, filtering food all the while. Skimmers include the right whales, pygmy right whales, and bowhead whales)
Swallowers and skimmers:
Sei whales do both.
Benthic (bottom) feeders:
They vacuum the mud on the ocean floor. Grey whales are benthic feeders.
 
Baleen whales evolved about 35 million years ago, during the early Oligocene Epoch. The earliest baleen whale fossils are from New Zealand.

CLASSIFICATION OF BALEEN WHALES

Family Eschrichtiidae:
The Gray whale(Eschrichtius robustus) is the only bottom feeder. As it swims along the bottom of the ocean stirring up sediment, it takes the nutrient-rich murky water into its mouth, and forces it out through its short baleen, retaining tiny organisms.

Family Balaenopteridae (the rorqual whales; rorqual is Norwegian for furrow):
These whales have 25-100 parallel throat grooves that extend from the throat to the flippers. When they eat, these grooves expand, allowing them to take huge gulps of water, forcing it through their short baleen to filter out tiny organisms. They have long, sleek bodies, a median notch, and a small dorsal fin.
Subfamily: 
*Blue whale(Balaenoptera musculus)
*Bryde's whale(Balaenoptera edeni)
*Fin whale(Balaenoptera physalus)
*Minke whale(Balaenoptera acutorostrata)
*Sei Whale (Balaenoptera borealis)

Subfamily Megapterinae(long flippers with rough edges):
*Humpback whale(Megeptera novaeangliae)

Family Balaenidae:
The right whales swim along the surface open-mouthed, skimming the water with long, fine baleen. They have no dorsal fin, no throat grooves, and a huge, arched jaw.
*Bowhead whale(Balaena mysticetus)
*Northern Right whale(Eubalaena glacialis)
*Southern Right whale(Eubalaena australis)

Family Neobalaenidae:
bowed head, short baleen, falcate dorsal fin.
*Pygmy Right whale(Caperea marginata)

Family Cetotheriidae:
This family is extinct.
*Cetotherium: an extinct, early baleen whale from the mid to late Miocene. 13 feet (4 m) long. It looked like a small gray whale.