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The animal on the cover of Angular: Up and Running is a tub gurnard (Chelidonichthys lucerna). This fish is a bottom-dweller found around the Mediterranean and Atlantic coasts of Europe and Africa. Gurnards are also known as sea robins because the swimming motion of their fins resembles that of a flying bird (and one species, Prionotus carolinus, has an orange belly). The gurnard makes a unique croaking or grunting noise, generated by squeezing a muscle against its swim bladder—this sound is commonly heard when they are caught by fishermen.

The tub gurnard is the largest gurnard species. It is primarily red in color, with a bony armored head and large blue pectoral fins. These fins contain sensitive feeler-like spines that help the fish explore the seabed for food, such as smaller fish, crustaceans, and carrion.

In the past, the bony gurnards were often considered bycatch and discarded (or used to bait lobster and crab traps). But as other marine species have become overfished, gurnards are becoming more popular in the seafood industry. Their flesh is firm and holds together well in soups and stews, such as the French bouillabaisse.

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 from Meyers Kleines Lexicon. 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.