You can read more here about leptocephalus/ baby eels, including how they use an internal goo instead of blood, but still somehow manage to have fangs and a shocked expression that is *very relatable*.
The marine eels and other members of the Superorder Elopomorpha have a leptocephalus larval stage, which are flat and transparent. This group is quite diverse, containing 801 species in 24 orders, 24 ...