True solesSoleidae

The best known fish in this family is a sole from this sea that defends itself with chemistry. At the base of every dorsal and anal fin ray the finless sole carries a pore, and each pore leaks a milky fluid that foams in seawater when the animal is bitten or squeezed. A shark that takes one into its mouth lets go at once. That experiment, run here in the 1970s, belongs to the species page.

What the family page can add is what became of the milk. Its active ingredient is pardaxin, a short peptide that slots itself into a cell membrane and opens a hole in it, working alongside steroid compounds that are closer to soap than to venom. Nobody ever turned the mixture into the shark repellent divers were promised, because it takes more material than an animal can carry and the sea washes it away, but the molecule left the fish and is still worked on in laboratories, tested against bacteria and against tumor cells.

Chemistry is a reasonable answer for this body. A sole has no speed, no spines, no cover and no way to threaten anything at all. It is a thin oval with both eyes on the right side and a fringe of fin running unbroken around the whole margin, and it is under the sand within a second of landing.

The head is the other thing worth a look. The mouth is small, set low and twisted toward the blind side, and the blind side of the head carries a beard of short fleshy filaments. A sole does not ambush anything. It works the sediment face down, reading it by touch and by smell for worms and small crustaceans, mostly at night, and it never needs to see any of them. Four are listed here, none of them longer than a hand.