An anatomical map of squid lateral lines

Survival of aquatic animals requires sensing water movement. In both aquatic vertebrates and cephalopods, sensory cells arranged in 'lateral lines' on the surface of the animal detect water motion relative to the animal's body with mechanosensitive hair bundles¹. Cephalopod lateral lines differ from those of fishes in hair bundle cytoskeletal composition, morphology, and receptor cell location. Fish have lateral lines arrayed on the head and body, whereas squid lateral lines, also termed epithelial lines or lateral line analogs, have only been described in detail on the head and arms^2,3; it is an enigma how the rest of the animal's body detects local water movements. We asked what anatomical features exist on the mantle of squid Doryteuthis pealeii that may allow it to sense water motion. We examined free-swimming paralarvae and uncovered a complex organization of lateral lines varying in hair bundle density, anatomical position, and length. Across the animal's surface, hair bundles are organized into discrete dense lines or broad fields, unlike those described previously in fish or cephalopods. The mantle bears stereotyped arrays of hair bundles that we term mantle lateral lines. Neuronal processes from the mantle lateral line cells project to the stellate ganglion. Our results show that the whole squid's surface is elaborately ornamented with varied lateral lines that likely register specific types of local water movements.