This Actinotocarcinus chidgeyi crab is a very rare and extinct, spider crab from New Zealand. They are also really tough to prep because of those very delicate spikes on the carapace that can shatter if you bring the air scribe too close to it.
Watch it being found and prepped on YouTube
Age: ~12 million years old (Miocene)
Location: South Island, New Zealand
Size: 6cm long, 6cm wide, 5cm high (2.4" x 2.4" x 2")
Weight: 327g (0.7lbs)