leptocephalus vs larva

leptocephalus and larva both are nouns.

Word	Noun	Adjective	Verb	Adverb
leptocephalus	Yes	No	No	No
larva	Yes	No	No	No

As nouns, larva is a hypernym of leptocephalus; that is, larva is a word with a broader meaning than leptocephalus:

leptocephalus: slender transparent larva of eels and certain fishes
larva: the immature free-living form of most invertebrates and amphibians and fish which at hatching from the egg is fundamentally unlike its parent and must metamorphose

leptocephalus (noun)	larva (noun)
slender transparent larva of eels and certain fishes	the immature free-living form of most invertebrates and amphibians and fish which at hatching from the egg is fundamentally unlike its parent and must metamorphose