This shell-less mollusc is found in tropical and sub-tropical waters in the epipelagic zone of the world's oceans.
Subsequent authors corrected this to F. desmarestia, but according to the rules of precedence of scientific names, the misspelling should stand.
[2] Firoloida desmarestia has a proboscis, a long, transparent cylindrical body and a short, ventral tail.
It has a large, rounded swimming fin, situated towards the front of the mollusc, and the opaque visceral nucleus, a mass which includes the liver, heart, gonad, sexual glands and kidneys, at the rear.
Newly fertilised eggs are close to the visceral nucleus while veliger larvae, complete with a shell of two whorls and a rounded aperture, are at the far end and eventually become detached.