Mysticeti (baleen whales)

Baleen plates of a Bryde's whale foraging

Successfully toothless in the ocean

Baleen whales (suborder Mysticeti) are large cetaceans with the distinctive feature of not having teeth. They have baleen instead, a comb-like structure hanging from the upper jaw, made of plates that are partially overlapped and act like a filtering apparatus.
Baleen plates are made of keratin, the same protein that composes our fingernails, the horn of the rhino, the hooves of a cow, etc.

General characteristics

Baleen whales have two blowholes, whereas toothed cetaceans (suborder Odontoceti) have only one.

The two blowholes of a Fin whale
Females are larger than males, although sexual dimorphism is less marked as it is in most odontocetes, for which males are bigger than females.
Throat pleats (grooves) of a Bryde's whale (family Balaenopteridae)

Taxonomy

Suborder Mysticeti comprises 4 families, for a total of 15 species.
  1. Balaenidae
  2. Balaenopteridae
  3. Eschrichtiidae
  4. Neobalaenidae

Family Balaenidae

It comprises 4 species:
  1. Bowhead whale (Balaena mysticetus)
  2. North Atlantic right whale (Eubalaena glacialis)
  3. North Pacific right whale (Eubalaena japonica)
  4. Southern right whale (Eubalaena australis)
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.

Family Balaenopteridae

It comprises 9 species and the animals belonging to the Balaenopteridae family are also called rorquals:
  1. Antarctic minke whale (Balaenoptera bonaerensis)
  2. Blue whale (Balaenoptera musculus)
  3. Bryde's whale (Balaenoptera brydei)
  4. Common minke whale (Balaenoptera acutorostrata)
  5. Eden's whale (Balaenoptera edeni)
  6. Fin whale (Balaenoptera physalus)
  7. Humpback whale (Megaptera novaeangliae)
  8. Omura's whale (Balaenoptera omurai)
  9. Sei whale (Balaenoptera borealis)
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.

Family Eschrichtiidae

The family is monotypic - i.e. it contains a single species:
  1. Gray whale (Eschrichtius robustus)
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.

Family Neobalaenidae

The family is monotypic - i.e. it contains a single species:
  1. Pygmy right whale (Caperea marginata)
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.
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