According to Leslie...
"It's a pelagic snail in the family Carinariidae. There's at least one IP species that has brown pigment along the tail -
Carinaria cristata - so it may be that. Pelagic snails are pretty fantastic. Shells are reduced or even absent while bodies are translucent to completely transparent. Usually the only parts visible are the eyes, mouth parts, and stomach areas. They're voracious predators of other pelagic critters such as salps, chaetognaths, and other snails."
Carinariidae
Carinaria cristata
Cardiapoda richardi
Thank you, Leslie!
__________________
The way is to the destructive element submit yourself,
and with the exertions of your hands and feet in the water
make the deep, deep sea keep you up...
Joseph Conrad, Lord Jim.