Watarigani

Only the tips of its hind legs flatten into paddles, and it swims by working its whole body with each stroke. It's prized for the rich roe packed under its shell and for the savory broth that seeps out when it's simmered whole, valued more for what the shell releases than for the meat alone. Just before autumn-to-winter spawning, a female's roe fills out and the flavor deepens, while the flesh itself is fibrous and easy to flake into soup.

Its paddle-legs make it a strong swimmer, and it also burrows into sandy mud, so it's often caught in pots or bottom trawls. Its pincers are strong enough to injure handlers, so they're tied shut after landing. Simmering it whole, shell and all, in soup or pasta is said to draw out flavor that would otherwise stay locked inside, and using the whole crab this way is a deeply rooted way of cooking it.

It favors shallow, nutrient-rich inner bays, and waters like Mikawa Bay, fed by rivers, have long served as its fishing grounds. Its strong swimming ability lets it range across open tidal flats and shallow sandy-mud bottoms in search of the small fish and shellfish it feeds on, a body suited to life in an inner bay's ecosystem. Growing in such a nutrient-rich brackish environment is thought to be what packs its roe so densely.