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The animals on the cover of Network Security Assessment are porcupine fish (Diodon hystrix). This fish is found in oceans throughout the world, most often among or near coral reef areas. Its tube-shaped body ranges in length from 3 to 19 inches with relatively small fins. When threatened, the fish inflates itself by taking in tiny gulps of water until the stomach is full; the body expands in seconds to double or triple size, and its spines become erect. (Smaller species have spines that are permanently bristly.) The porcupine fish is covered with evenly spaced dark spots, which distinguishes it from other puffers.

The fish has a a single tooth in each jaw; fused at the midline, they form a parrotlike beak. A nocturnal hunter, it moves its body over a small area of sand and spurts tiny jets of water to uncover its prey, usually mollusks and crustaceans. The porcupine fish is popular as an aquarium specimen; it’s also blown up, dried, and sold as a souvenir.

In earlier centuries, certain Pacific island warriors used the porcupine fish to fashion a battle helmet. They would catch a fish, let it inflate, and then bury it in sand for about a week. When dug up, the fish, now a hard ball, would be cut open to make a hard, head-shaped piece that looked most formidable. The porcupine fish isn’t listed as endangered or vulnerable with the World Conservation Union.

Many of the animals on O’Reilly covers are endangered; all of them are important to the world. To learn more about how you can help, go to animals.oreilly.com.

The cover image is a 19th-century engraving from the Dover Pictorial Archive. The cover fonts are URW Typewriter and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.