All of the above animals are robust and have an arched upper jaw to accommodate the very long, finely fringed baleen plates.

They have a large head, which can span about 1/3 of the body length. The upper jaw is thin.

The animals belonging to the Balaenidae family lack throat grooves and dorsal fin.

All members have 7 cervical vertebrae, which are fused together.

All of the above animals are slender and have short baleen.

All Balaenopterids are streamlined, which makes them fast swimmers. The Humpback whale is a bit of an exception, as it a slower swimmer than the other members of the family and it is more robust.

Rather than being arched as in Balaenids, the upper jaw is flat.

The baleen plates are relatively short and not as finely fringed as in Balaenidae.

Balaenopterids present numerous throat grooves, which expand like an accordion and allow an even larger amount of water to flow into the mouth. Furthemore, expansion of throat grooves creates a depression (lower pressure) in the the oral cavity that eases water flow.

All family members have a dorsal fin which, in proportion to body size, turns out to be smallest in the biggest of all animals: the Blue whale.

The cervical vertebrae are unfused.

The Gray whale presents characteristics that are somewhat intermediate between Balaenidae and Balaenopteridae.

Like in Balaenids, the upper jaw is arched, a dorsal fin is absent and a hump followed by knuckles is observed instead. The Gray whale is a relatively slow swimmer. Like in Balaenopterids, the baleen plates are short and they are actually shortest than in any other mysticete cetacean.

Gray whales have 2-5 throat grooves and, unlike any other baleen whale, they forage at the bottom (although they are also known to feed at the water surface) where they filter crustaceans such as amphipods out of sediment and water.

The only remaining Gray whale populations inhabit the North Pacific Ocean as they got extinct in the North Atlantic many centuries ago.

There is no record of the Gray whale in the Southern Hemishpere.

It is the smallest of all baleen whales and only inhabits the Southern Ocean - i.e. the waters south of 60°S encircling the Antarctic continent.

The pygmy right whale represents a very rare sighting and for this reason it is a poorly studied animal.

As in Balaenids, the upper jaw is arched but unlike them a small dorsal fin is present far back.

It appears to feed mainly on krill.