The ocean quahog — a species of clam that lives in the North Atlantic — likely doesn't come to mind.
But this chart by Niall McCarthy, based off data collected by Discovery News, shows an interesting point: almost all of the longest-lived animals on Earth are in the ocean. And several of them can survive for two centuries or more.
Why are these species capable of living for so incredibly long? One commonality is that in many cases, either their size (as with the bowhead whale) or some sort of external protection (the quahog or red sea urchin) makes them virtually immune to predators.
"When an animal can survive for longer, there's a selection for genes that provide longevity, because they can provide a real advantage," Jay Olshanksy, a public health researcher who studies aging, told me last year for an article about the naked mole rat, a rodent that can live for up to 30 years.
When predation isn't a threat, there's a big evolutionary advantage in developing physiological systems that allow an animal to live longer — since it can mean producing more offspring — and all that investment won't get wiped out if a random predator were to come by for a meal.
When predation is a constant threat, though (as is the case for the vast majority of animals), there's no selective pressure that leads to animals evolving to live for centuries. A good analogy is a car: if you bought a junker you knew would break down in 10,000 miles, it wouldn't make sense to invest in a high-end stereo.