By Harold McGee
Spiny sea urchins are members of the animal group called echinoderms (Greek for “prickly skin”), which may account for 90% of the biomass on deep-sea floors. There are about a half dozen commercial species of sea urchins with average diameters of 2.5–5 in/6–12 cm. They’re almost entirely enclosed in a sphere of mineralized plates covered with protective spines, and are collected mainly for their golden, creamy, richly flavored reproductive tissues, which can account for up to two-thirds of the internal tissues. Both testes and ovaries are prized, and are hard to tell apart. Sea-urchin gonads average 15–25% fat and 2–3% savory amino acids, peptides, and IMP. In Japan, sea urchins are eaten raw in sushi or salted and fermented into a savory paste; in France they’re added to scrambled eggs, soufflés, fish soups and sauces, and sometimes poached whole.