A Guide to Crustaceans, Bivalves and Molluscs, or Why You Should Be Eating Exoskeleton-Bearing Aquatic Invertebrates

I grew up in a coastal fishing village in Maine, and one of my favorite memories is being out on the flats at low-tide, digging for the clams that would accompany our occasional lobster feasts (back when lobster was well under a dollar a pound). I can still feel the excitement of pulling that clam rake up and looking for the tasty bivalves that would soon become the first course.

We humans like our shellfish. Nearly every coastal region which hosted humans features massive shell collections, often called shell heaps, or middens. You’ve even got inland piles, like the 11,000 year old midden full of snail shells in inland Vietnam, indicating that even inlanders knew shellfish were worth eating. Back in my marathon training days, I recall running a mountain trail in Woodside, CA, ten miles inland, and coming across layers of thousand year-old strata embedded with all manner of seashell left behind by the coastal Indian tribes. Because the entirety was just full of seashells, you had to look closely to discern the individual shells. These folks definitely liked their shellfish.

Recounting a classic Weston A. Price observation, Chris Masterjohn describes how two perpetually warring New Guinean tribes would broker temporary peace to trade shellfish for sweet potatoes. The upland tribes would put aside the spears and bring down some tubers, while the coastal tribes would relent and offer shellfish. It was a beautiful arrangement, far more harmonious than the alternative (which sometimes occurred) – the highlanders selectively hunting and eating the livers and organs of fishermen of the coastal tribes.

But why? What can explain the persistent shell middens all over the world, both inland and on the coasts? Why were there so many seashells embedded in that Woodside strata? What’s so great about shellfish that it stops multigenerational tribal warfare in its tracks and drives sweet potato eaters to prize the organs of fishermen who eat it?

They’re tasty, sure, but I wouldn’t put oysters, mussels, and clams over a grass-fed lamb shoulder roast, and I doubt the flavor of those New Guinean fisherman livers reflected the shellfish content of their diet. No, the taste isn’t the driving factor. It’s the uniquely dense nutrition inherent to most shellfish. Since they spend their lives immersed in mineral rich water, they’re excellent repositories of those same minerals, including zinc, iodine, selenium, and magnesium, along with vitamin A and B-vitamins (especially B12). Plus, when we eat shellfish, we’re eating the entire animal (except for the shell). All that muscle meat and digestive tissue and organ mass slides right down. Humans can get these nutrients on land through other animals and some plants, but rarely can they get them in such a concentrated, easy-to-consume form. And you all know how much we like to make things easy for ourselves.

Let’s go down the list of species and make a case for including shellfish in your diet:


The most nutrient dense, the most expensive, the perfect accompaniment to lemon and hot sauce, oysters are truly the stars of the shellfish world. Recent evidence of an early “oyster bar” puts our infatuation with the bivalves at around 125,000 years old, which is a pretty strong track record. The oyster’s reputation as an aphrodisiac may have ground to stand on, as they are the single greatest source of dietary zinc, which our body needs to make testosterone.

Just four medium sized Pacific oysters supply a smattering of B-vitamins (including over 1000% of daily B12), 1200 IU of vitamin A, a third of daily folate, almost 7 mg of vitamin E, 3 mg copper, 280% of daily selenium, and 33 mg zinc. That comes with 18 g protein, 4 g fat, 1.5 g omega-3, 0.1 g omega-6, and 9 grams of carbohydrates.

At an Asian supermarket, I can buy those four oysters, still living, for $0.80 a pop. Or, I can head down to Malibu Seafood and pick up some for a couple bucks each. As to whether farmed oysters, which make up 95% of the market, are okay, they’re fine. If you remember from last time, I described how most farmed shellfish live totally “natural” lives, only instead of being attached to a rock they’re attached to an artificial construct. Same water and food, though. Eat these guys raw and living for the full effect (plus briny goodness). Canned, smoked oysters are also an option.

How to open oysters.


As a New England native, I’m contractually obliged to sing the praises of the clam. Now, they aren’t quite as nutrient-rich as oysters, but they’re still worth eating for a few reasons. First – the texture. Some people hate the chewiness; I love it. I can understand if you get clams cooked to the consistency of rubber, as many restaurants do, but not every food has to be tender. Frankly, I’d find it a little unsettling if clams just disintegrated in my mouth. Second, the versatility. Clams definitely have a flavor – they aren’t blank canvases – but it’s a flavor that lends itself to a lot of cooking styles. Spicy stir fried Asian clams? Yep, works. Steamed with butter, garlic, and white wine? Great stuff. And of course you’ve got New England clam chowder, which – by itself – justifies the presence of clams on this planet.

They’re also nutritious. Fifteen medium raw clams (mixed species) gives a nice dose of vitamin A, B12, selenium, magnesium, and iron, plus 31 g protein, 7 g carbohydrate, and 300 mg omega-3.

Most clams are farmed, and that’s okay.

Try making arctic char chowder, only with clams.


When I was younger, mussels were more of a low-end shellfish that I avoided (after all, you could find scads of them clinging to every dock piling on the East Coast). With their appearance on more gourmet menus lately, I’ve taken a shine to them. In the shell, cooked in white wine, garlic, and butter, with about a cup of savory mussel broth left over is just incredible and super easy. Fast, too. It only takes me ten minutes to throw a big batch together. In fact, I could probably squeeze one in right now… Great. Now I’m hungry for mussels. Hold on while I fix some.

In my last post on farmed seafood, I gave credit to the incredible nutrition of the New Zealand green-lipped mussel, which I love but have only had frozen. I can only imagine them fresh. Standard blue mussels are very nutrient-dense, too. 20 medium sized raw blue mussels provide folate (1/3 of the RDA), good amounts of B-vitamins including thiamine, riboflavin, and B12, 108 mg magnesium, 12.6 mg iron, four days’ worth of manganese, 143 micrograms selenium, and 5.1 mg zinc. Along for ride are 38 g protein, 11 g carbohydrate, and 7 g fat, including 1.5 g omega-3 and just 100 mg of omega-6.

I’d be leery of farmed Asian mussels, but all other sources are fine.

Try tomato garlic mussels.


Sweet, succulent scallops, formed into perfect bite-sized morsels. They almost seem designed specifically for eating, with their flat, even surfaces (good for searing), uniform, attractive color, and natural sweetness. Compare the scallop, which looks like it was formed in a mold, to the oyster, that delicious but shapeless blob of slime and salt, and you see why squeamish folks will shun shellfish but happily eat the scallop.

Just because the masses love ’em doesn’t mean they aren’t good for you. On the contrary, a mere six ounces of scallops provides the RDA for B12 and a decent mix of magnesium, selenium, and zinc, plus 20 grams of protein. Farmed and wild scallops from all over get a good rating from the Seafood Watch, so have at them.

Try scallops and bacon.

Lobster, Crab, and Crayfish

Lobster, crab, and crayfish aren’t what most people typically think of when discussing shellfish. They are arthropods, rather than mollusks. They walk around and actively eat things, instead of being filter feeders. They have big claws. Are they encased in shell? Yes, and so they are included.

The nutrition data available for lobster, crab, and crayfish indicate decent levels of magnesium, selenium, and zinc, more so for crab and lobster than crayfish, probably because the former are sea creatures and the latter is freshwater. As this article points out, conventional data most likely doesn’t account for the viscera, or connective tissue and organ mass; it’s only concerned with the muscle meat. If the nutrition data for the organs of other animals is anything to go by, eating the viscera of arthropods is certain to provide a wider, denser range of nutrients. So that means eating the crab and lobster “butter” and sucking out the contents of the crayfish head are probably good ideas.

All crab and lobster are wild caught and good to eat. Farmed American crayfish is safe and plentiful.

Try lobster, grapefruit, and avocado salad with creamy citrus dressing.

Sea Snails

Two main types of sea snails are usually available for purchase: whelks and conchs. Usually available is relative, of course. You probably won’t find these at Safeway. To distinguish between the two, rely on the labels or the guy working the seafood counter. Conch shells tend to be a bit more ornate looking, almost with a crown-like structure or “horns”, while whelks do not. It’s easy to mix them up. Conch shells double as wind instruments, like in “Lord of the Flies.” I’ve never had whelk, but conch ceviche is incredible.

Three ounces of raw whelk (unspecified species) meat contains a day’s worth of copper, 4.3 mg iron, 73 mg magnesium, and 70%, or 38 micrograms, of selenium, plus plenty of B12. You also get 20 g protein and 6 g carbs, but sadly no fat. Four ounces of cooked conch meat gives you 17 g protein, a third of the recommended folate intake (121 micrograms), 4.3 mg vitamin E, and a day and half’s worth of B12. As for minerals, the conch provides 161 mg magnesium (a huge amount), 0.3 mg copper (a third of the RDA), and half the RDA for selenium.

Unfortunately, conch gets an “Avoid” rating from the Seafood Watch. There are sustainable farms popping up in the Caribbean, but for now it might be a good idea to hold off on the wild conch.


See this recent post.

Shellfish Allergy

Shellfish allergy is one of the most common, and this leads some to believe that shellfish may be a novel addition the the human diet to which a good chunk of people have yet to adapt. This is a mistake. First, we’ve obviously been eating shellfish for hundreds of thousands of years. They don’t run from us, they taste great, and we’ve got the shell remains to prove it. Second, beef allergy is one of the more common allergies, too (more common than you might think), but that doesn’t tell us anything about whether we should be eating it or not. It does suggest that folks who are allergic to a particular food probably shouldn’t be eating the food, and that’s it.

If you haven’t been eating shellfish on a regular or semi-regular basis, I think I’ve shown that you probably should be. We have every indication that our ancestors prized the shellfish and considered it a sacred food worthy of trekking long distances and even commiserating with mortal enemies. The nutritional data we have on the various types of shellfish confirm that these little guys are indeed powerhouses.

If the cost of shellfish seems prohibitive, understand that you don’t have to, nor should you, get the bulk of your animal nutrition from them. The fact that they are so nutrient dense means you only need a few to get the benefits. Don’t necessarily think of oysters, mussels, and their brethren as protein sources. Think of them as whole food supplements.

What’s your favorite type of shellfish? Do you eat it regularly? Do you think you’ll try adding more to your diet?

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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