Aetomylaeus vespertilio has a maximum size of around 240 cm in disc width and a clearly distinct pattern of reticulate dark lines and rings on its back.

If the extremely long tail is unbroken, it can considerably add to the maximum body length of 4m.

Aetomylaeus vespertilio can be spotted up to 110 meters deep along the coasts of Australia, China, India, Indonesia, Malaysia, Maldives, Mozambique, Palau, Philippines, Seychelles, South Africa, Taiwan, and Thailand.

Despite the wide range it can be spotted at, it is rarely observed, and has been suspected to have had a large population decline within the past three generations.

There have been fewer than 60 confirmed sightings of Aetomylaeus vespertilio, giving it the nickname 'the unicorn of the sea.