Horsehair crab

A Horsehair Crab (ケガニ, Kegani) is a type of deep sea creature that is introduced in and can be found at the bottom of the sea. The Horsehair Crab appears from November to April all day long, and sells for 4,000 Bells. It is indicated by a circular shadow. Diving is the only way of capturing it.

In New leaf
"Horsehair crabs get their name from their spiky hairs, which can hurt, though they have soft shells. They inhabit the bottom of fairly shallow waters, with their biggest predator being the octopus. They camouflage themselves by putting dirt on their hair so they don't stand out in the sand. Their shells house a tasty portion of innards, so this species is a favorite of those who enjoy crab."