shrimp, (kokuji)
蛯 centers on shrimp, a small aquatic creature. It is a kokuji, a kanji created in Japan specifically for this meaning.
蛯 is a Japanese kokuji, combining 虫 (insect/creature) with 老 (old), likely to represent a shrimp as an old-looking sea creature. The exact historical reasoning is uncertain.
The left side 虫 suggests a small creature, and the right side 老 (old) can remind you of the curved, whiskered appearance of an old shrimp. Together they make 蛯, a shrimp.
For えび, picture an elderly shrimp with a long beard, and think of 'ebi' as the sound it makes when it snaps its tail: ebi -> えび.
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