This baby nautilus emerged this week from an egg laid last November at San Diego's Birch Aquarium. For this tiny cephalopod, the process of being born took not hours, or even days, but weeks. The ZooBorns site has a series of photos that show how the nautilus slooooooowly emerged from the egg.
Biologists don't know exactly why this process takes the nautilus so long.
For one thing, they're difficult to breed in captivity. (It's not panda hard, but not simple, either. This was the first egg to actually hatch at the Birch Aquarium, out of 40 laid over the last 3-4 years.) The first captive nautilus hatchlings weren't recorded until 1990. We've still got a lot to learn about them.
One thing we do know, though, is that baby nautiluses don't seem to come with any special apparatus for breaking themselves out of the egg. In contrast, most birds and reptiles (as well as some frogs, spiders, and egg-laying mammals) have what's called an "egg tooth" — sort of nature's bottle opener for egg-bound embryos. Lacking that, nautilus hatchlings are basically forced to wiggle their way out of the egg along the line where a seam of capsule splits.
That's exhausting work, especially for a creature only 3cm long.