A massive swarm of thousands of crabs has been discovered near the seafloor off the western coast of Panama.

Video footage shows the swarm of five-inch-long crabs, which resemble small lobsters, amid clouds of sediment at a depth of 355 to 385 meters. Researchers from Woods Hole Oceanographic Institute and their colleagues stumbled upon the throng during the final dive of an expedition to the Hannibal Bank seamount, a submerged mountain that is rich in marine life. A paper describing the event was published Tuesday in the...