Image of a glass squid, an animal that lives 200m to 1km under the ocean's surface.
When threatened, the mesopelagic Cockatoo Squid, Cranchia scabra (a Glass Squid), can pull its head and tentacles into its mantle and turn into a ball. Sometimes the squid arranges its tentacles into a crest like a cockatoo’s (bottom)—thus its common name, “Cockatoo Squid.” This squid has small, knoblike, cartilaginous tubercles all over its body (seen clearly in the middle image) and has 14 oval photophores on each eye that produce greenish light (bioluminescence). When aggravated, the squid waves its arms back and forth at whatever it perceives as a threat (top).
Credit: Danté Fenolio. This image is taken from his book Life in the Dark, published by Johns Hopkins University Press.