You'll need to look very closely to find this transparent heteropod. Except for food in the gut and black pigment in the eyes, this species is nearly invisible. The elongate body lacks a shell, a trait typical of pterotracheid heteropods. It is cylindrical in cross section, with a body length to 4 cm. The visceral mass is relatively small and situated posterior to the ventral swimming fin.
Males possess a sucker on the ventral fin and a pair of tentacles behind the eyes.
Females are distinguished by the permanent egg filament that trails from the posterior end. Various types of bioluminescent animals, jellyfish, siphonophores, crustaceans and salps are favored prey. Firoloida typically hunts at night while drifting motionless with the ventral fin hanging down. This species has a cosmopolitan distribution throughout tropical and semi-tropical seas. It occasionally ventures into surface waters as far north as southern and central California, but only during periods when warm oceanic water moves inshore.