|Binomial name||Cystophora cristata|
The hooded seal gets its name from an inflatable bladder. The bladder hangs over the eyes and down over the lips when deflated. They can also inflate the bladder, which they do before making their initial breath before diving underwater. They can then inflate and deflate the bladder as they are swimming.
The inflatable bladder is used for acoustic signaling, threatening other species when competing for food. The bladder also communicates information about their status and health to other members of the species.
Only males have the hood, which they develop at the age of four. Females do not grow the bladder.
Males also have a membrane that extends from the left nostril. The membrane is balloon-like and helps to attract a mate.
The nostril membrane produces different sounds when shaken, depending on if underwater or on land. These signals can be used for sexual purposes to attract a mate, but mainly for acoustic situations and signaling.