tadpole
蝌 refers specifically to a tadpole, the aquatic larval stage of a frog or toad.
蝌 combines the insect radical 虫 with 科, which likely provides the sound カ. The character is used specifically for tadpoles, though the historical reasoning behind the component choice is not fully clear.
An insect-like creature 虫 that is measured or classified 科 as a tadpole: the wriggling shape and aquatic nature fit the insect radical, while 科 suggests a category of small water life.
For カ, imagine a tadpole in a jar labeled 'KA' (like the first syllable of 'tadpole' reversed): the jar's label cues カ while the tadpole swims inside.
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