Squid have hundreds more sensory cells than scientists realized, with hair bundles that may help explain how human hearing works and breaks down.

Water flowing over a squid’s head and arms brushes tiny past bundles of hair-like projections that help the animal sense movement around it. Scientists have known about these sensory structures for years, but they had only a partial picture of how widely this equipment was spread across the squid’s body.

Brian McDermott and his colleagues at Case Western Reserve University have now found hundreds more of the cells carrying these bundles, extending across the animal’s entire surface. Their research, published in Current Biology, includes the first complete map of squid lateral lines, arrays of sensory cells known as hair cells. The newly revealed network could give researchers another way to investigate the delicate structures that make human hearing possible.