This creature is a kind of larvae of marine fish and some other sea eel species. It has the scientific name of Leptocephalus.
Glass eel.
Leptocephalus has a flat and transparent body like glass, so they are also called glass eels .
For more context, see Unexpected discovery of transparent glass like fish,.
Leptocephalus larvae are only 5-10cm long on average, some cases can be as long as 30cm.
They usually live at a depth of 100m below the sea surface. When in the form of larvae, their bodies consist of a jelly-like substance that can see through, but as adults, glass eels will undergo a period of transformation, the tissues gradually become colored and no longer in all the time.
