What throat feature gives rorqual whales their expandable feeding capacity?

Ventral pleats are the throat feature that gives rorqual whales their expandable feeding capacity.

These longitudinal folds of skin and underlying tissue run from beneath the mouth toward the navel. During a feeding lunge, a rorqual opens its jaws and engulfs a huge volume of water containing krill or fish. The pleats unfold like an accordion, allowing the throat and mouth region to balloon before the whale contracts them again.

Once the mouth closes, the whale pushes water back through its baleen plates with the tongue. The baleen acts as a filter, retaining prey while water escapes. This engulfment-and-filtering method is called lunge feeding and is especially dramatic in blue and humpback whales.

The feature is also called throat grooves or ventral grooves. It is an important distinction from right whales and bowhead whales, which lack the long expandable pleats characteristic of rorquals. The sei whale and common minke whale have comparatively shorter grooves.