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Which cephalopods do not have an ink sac?

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A blue-ringed octopus with bright blue rings on its beige body crawls over a rocky, coral-strewn seabed. — cephalopod Blue-ringed octopus (genus *Hapalochlaena*).

While most cephalopods possess an ink sac used for defense, there are notable exceptions among these mollusks. Specifically, the primitive Nautilus and certain species of deep-sea octopuses do not have an ink sac.1

Unlike modern coleoids—which include squids, cuttlefishes, and most octopuses—the Nautilus relies on its external shell for protection rather than the ink-based defense mechanism found in its more active, shell-less relatives.1