pollywog vs larva

pollywog and larva both are nouns.

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

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

pollywog: a larval frog or toad
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

pollywog (noun)	larva (noun)
a larval frog or toad	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