Re: How long does the average mollusk live?

Wow, this is a very broad question! The Mollusca are one of the largest and most diverse phyla in the animal kingdom, and I have no idea what the "average" mollusk is; I suspect that it depends on who is asking the question. However, I did a bit of searching and was able to find information on longevity for some of the major molluscan groups. I hope it helps you.

The Gastropoda (snails, limpets, slugs, etc.) are the largest class of mollusks. Longevity in these animals varies quite a bit, from as short as a month for some of the flamboyantly colored marine nudibranchs, to upwards of 20 years in large snails such as conchs. Land snails, which you may have seen demolishing plants in your vegetable garden, probably live a few years.

The Bivalvia are probably most familiar to you as clams, mussels, oysters, and scallops. These animals are slow-growing and can live for decades. In fact, this report describes how one bivalve was estimated to be 220 years old. This may well be the longest-lived animal on the Earth!

The Cephalopoda are the (mostly) shell-less, highly intelligent mollusks such as squids, octopi, and cuttles. Incidentally, they are some of my favorite animals. Most of the cephalopods are semelparous and short-lived. Being semelparous means that they reproduce only once, then die soon after. Squids generally live about a year, and octopi and cuttles live from 1-4 years, depending on the species. The nautili (plural for "nautilus"), which are the only cephalopods that have an external shell, are also the longest-lived; biologists estimate that they can live up to 20 years. As you might expect, the nautili, being such long-lived creatures, are also suspected to be iteroparous (they mate more than once), although they are such secretive animals that biologists aren't entirely certain about this.

So, depending on whether your "average" mollusk is a snail, a clam, or a squid, these guidelines should help you guesstimate how long it would live. I hope this is the information you were looking for.

Allison J. Gong
Mad Scientist