Sea urchins may look soft and squishy, but their spiny exteriors are actually incredibly strong and tough. This is due to the unique structure of their spines, which are made up of a combination of calcium carbonate and organic material. The calcium carbonate gives the spines their strength, while the organic material provides flexibility. This combination makes sea urchin spines incredibly resistant to damage, making them a formidable defense against predators.

A team of scientists at the University of California, Berkeley, recently used X-ray microtomography to get a closer look at the structure of sea urchin spines. They found that the spines are made up of a series of interlocking plates, which are held together by a network of collagen fibers. This structure creates a very strong and durable material, which is why sea urchins are able to withstand the attacks of predators such as fish and sea otters.

In addition to their strength, sea urchin spines are also very sharp. This is due to the fact that they are constantly growing and shedding. The new spines that grow in are always sharper than the old ones, which helps to keep the sea urchin well-defended.

The combination of their strong and sharp spines makes sea urchins a very difficult prey for predators. This is why they are often able to live in large numbers, even in areas where there are many predators.