Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
23 Jun

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?

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Well now I could go for a dozen oysters and a full-of-horseradish bloody mary…

    T wrote on June 23rd, 2011
  2. This reminds me of Primal Con. The night before it all started. Lars ordered the shellfish appetizer. In it was some shellfish and some crazy egg in some sort of wine glass. He swallowed it in about 3 bites. It was amazing.

    I am pretty sure there was oysters and mussles. Not sure what else.

    My favorite from this group is king crab and then scallops. I like mussels too.

    I have yet to try lobster, oysters, clams, crayfish and sea snails. Hey, I used to be afraid of all things that came from the sea for the first 21 years of my life!

    I can’t wait to try lobster tail though… I LOVED king crab so much that its one of my favorite foods now!

    Primal Toad wrote on June 23rd, 2011
    • don’t avoid the rest of the lobster. the claws are spectacular. I even like the legs, just suck on the leg like a straw YUM

      bbuddha wrote on June 23rd, 2011
    • Toad, if you haven’t tried lobster yet, I envy you so much! I’m from New Hampshire and my family has several giant “lobster feeds” every year. Start with the legs, sucking out the juice and the meat just like a freeze pop. Then detach each claw, drink the juice, and extract the meat, placing it in a bowl of melted butter to marinate. While that’s happening, take off the tail and eat the meat from the hind flippers like an artichoke leaf. Once you get the giant tail meat in the butter, start eating the claws. Oh man, I’m getting hungry just typing this. I’ve never eaten the cephalothorax before, but maybe I ought to start. Point is, don’t just eat the tail–you’ll be missing out. Good eating, man!

      Roger wrote on June 24th, 2011
  3. Hi Mark,

    Living on the West Coast of Canada, I am surrounded by exoskeleton-bearing aquatic invertebrates. In fact last Friday my wife and I went to a local shellfish festival where the appetizer was a competition between three different oyster growers and the meal was five different servings of shellfish (each serving accompanied by a different wine. Life is so boring :)

    Appropriately enough we live adjacent to ‘Midden Road’ and walk through a park, full of middens to get to the festival.

    michael wrote on June 23rd, 2011
    • The Comox shellfish festival by any chance?

      Johnc wrote on June 23rd, 2011
      • absolutely. good food. good fun. you in this area?

        michael wrote on June 26th, 2011
        • Yup, Merville actually. I’m normally not surprised to find a local person via something online but so far I’ve yet to meet anyone interested in (or who has even heard of) paleo in these parts so it’s a surprise!

          Johnc wrote on June 27th, 2011
        • John,

          I find the same. I’d like to find some more fans of this lifestyle around here. The resources are amazing. I get a 1/2 cow from Gerald Smith in Merville every year and lots of my veggies from Siefferts.

          email me direct at michael.smit1 at

          michael wrote on June 27th, 2011
  4. I missed Monday night oysters this week. Oopsie.

    Peggy The Primal Parent wrote on June 23rd, 2011
  5. Mark, fresh NZ mussels are AMAZING. I must have eaten piles of them as a kid living in New Zealand. We would walk along the beaches and rocks picking and eating as we went, lol! I can only get them frozen here, but i’ll eat them by the bowlful ^_^

    Nion wrote on June 23rd, 2011
  6. and don’t forget the omega-3’s!

    ottercat wrote on June 23rd, 2011
  7. Amazing headline. And an article that lives up to it.

    I usually only eat shellfish in restaurants, but I’m looking to learn how to prepare them myself and this article might give me enough of a bump to actually try it.

    Patrick wrote on June 23rd, 2011
  8. I was already sold on scallops and clams, but you just sold me on oysters too. As a testosterone junkie there is no way I can pass up the number-one whole-food source of zinc. I will grab some for lunch this very day.

    However, you’ve made me wonder if the best choice of all might be the raw livers of aboriginal fishermen. If anybody has a humane source for those, please let me know…

    Timothy wrote on June 23rd, 2011
    • Okay, I am now eating raw oysters right out of the jar. And I have to say that the epithet “briny goodness” applies to the nutritional profile, not the flavor. I’m no stranger to funky foods — adrenals, hearts, sardines — but man, these are really hard to get down. At least they chew up quickly.

      Please pass the fisherman liver.

      Timothy wrote on June 23rd, 2011
      • Add a splash of tabasco and a pinch of horseraddish and it will taste a lot better! Just had a dozen last night.

        Dave wrote on June 24th, 2011
      • I’ve never had them in jars, but I would be wary. Those jarred oysters are probably better for cooked preparations like oyster stew, or something where you obscure the flavor, like a shooter.

        Best way to get oysters is from a very VERY fresh source and right on the half shell with a little bit of lime and mignonette. It’s a totally different experience.

        Julia wrote on June 29th, 2011
  9. This was a great article! I love seafood and all of these exoskeletal creatures, except I can’t stand shrimp. To me it tastes sooo much different, and even the smell makes me queasy. Lobster, scallops, oysters are great…but no can do the shrimp.

    Nikki wrote on June 23rd, 2011
  10. Living up in the mountains i don’t eat as much as I used to…
    This post takes me back to netting crabs near Half Moon Bay & huckin ’em right into the pot when we got home. Or digging for pismo clams outside of San Luis Obispo. Stopping in Fisherman’s Warf for fresh goodies…
    Oh well, there is a decent sushi bar here. Maybe I’ll have some oysters tonight?

    peggy wrote on June 23rd, 2011
  11. Mark, I am so excited to learn that you are a fellow Mainer! My husband is an oyster lover and anthropology student, and we were just talking about taking a day trip up to Damariscotta to check out the Whaleback Shell Midden.

    Amy wrote on June 23rd, 2011
  12. I dislike oysters and am “meh” about mussels and shrimp, but love, love, LOVE scallops, clams, crab, lobster and crawfish. Since scallops, shrimp and lobster are the only seafood my picky teenager will eat, I make them as often as I can!

    Mmmm, bacon and scallops…dinner tonight!

    Jan wrote on June 23rd, 2011
  13. I wonder what it is that makes shellfish allergies so common? Out of all the many random things I’m allergic to, nothing gives me quite the severe reaction… which sucks because what I can remember having tried before was pretty darn tasty!

    Jennifer wrote on June 23rd, 2011
    • Allergies are often produced by the part of the immune system that defends against parasites (the IgE system).

      Any food that contains protein can induce an allergic response, but I’d guess that mammalian tissues are so similar to ours that meat is unlikely to cause problems. Shellfish and crustaceans are lot more different, so might be more prone to causing a false “parasite infection” alarm.

      Tim wrote on June 24th, 2011
  14. I am right on the coast in Florida now (I am from Agoura by you, Mark). SO fortunately I have access to lots of fresh seafood. We have lots of mizzens out here. Aside from bridges, they are the only hills 😀

    James Schipper wrote on June 23rd, 2011
  15. Lobster A-plus

    frank wrote on June 23rd, 2011
  16. Yuck. The one group I cannot seem to add to my diet no matter how hard I try. All of them make me very…. um… yeah…. squimmish is the best word for it.

    Jeanna wrote on June 23rd, 2011
    • I’m with you with the exception of shrimp and crab. Everything else I just cannot down it. And I did before too. There is just nothing redeeming about oysters, I’m afraid.

      Ute wrote on June 24th, 2011
  17. If the month doesn’t have an “R” in it, we’re out harvesting oysters up at the cabin. A truly delicious event. They’re also delicious steamed with some grassfed butter. MMMMMMMMMM good!

    Hal wrote on June 23rd, 2011
  18. Also, what would shellfish collection be considered – hunting, or gathering?

    Hal wrote on June 23rd, 2011
  19. Lobst-aah. I’m from Maine.:)

    Ashley North wrote on June 23rd, 2011
  20. Great post!

    We eat crab at least twice a month and I love to make muscles….haven’t had them in awhile, now I really want to eat them for dinner.

    I have never tried oysters they kind of gross me out, my husband loves them… he is from NOLA, so I don’t think he has ever come across seafood that he didn’t like.

    Nikki wrote on June 23rd, 2011
    • oh, NOLA is paradise for oyster lovers! the appetizer with three different varieties of oyster, three of granita and three of caviar would be on my “last meal” menu, if i get a chance to choose!

      i thoroughly adore all kinds of seafood, though.

      tess wrote on June 23rd, 2011
  21. Thanks, Mark, now you have me craving decidedly un-Primal linguine and clam sauce, one of my very favorite dishes in the world (been digging clams back home in CT for many years). Oh well, nobody’s perfect.

    pocopelo wrote on June 23rd, 2011
  22. You can collect barnacles from bridge pilings and make a great paleo soup out of them, packed with iron magnesium and iodine.

    I call it hungry hobo stew.

    rob wrote on June 23rd, 2011
  23. I’ve never liked seafood before but I’ve been trying to expand my horizons. One of the first things I did with my new boat was to go out and harvest some oysters from the public beds down here in Beaufort. Enough hot sauce and I can eat just about anything 😉

    I plan on making a habit of it.

    adam wrote on June 23rd, 2011
  24. I love mussels but developed a bad habit of sopping up the delicious garlic/wine sauce with crusty bread. That was before I went paleo. What do you use to sop up the juice if you don’t want to eat bread?

    Denise wrote on June 23rd, 2011
    • I suggest broccoli florets. They’re like edible paintbrushes!

      Timothy wrote on June 23rd, 2011
    • I had some really lovely mussels last night in a great buttery, lemony sauce with little bits of diced onion and garlic loitering at the bottom. Everyone kept offering me bread but I just took the slippery little critters out of their shells, dumped them all in the bowl and scooped them up (along with huge quantities of sauce and “debris”) with my handy-dandy spoon. No sopping required and I got to knock back way more of the delicious sauce than I ever managed with bread. Yum!

      Naptown Girl wrote on June 23rd, 2011
  25. I’m obsessed with scallops and shrimp. They’re so easy to cook in an instant via grill, searing or sauteeing in a stir fry!

    Clams, mussels, oysters not so much!

    thegetinshapegirl wrote on June 23rd, 2011
  26. Like I needed any more reason to eat shellfish?

    Peter@themensdomain wrote on June 23rd, 2011
  27. Ha Ha, as a coastal New Englander, I sure do love my shellfish…and since I developed a weird “finfish” allergy in my twenties..shellfish is the only “fish” I can work into my diet. Hello summer! Clamboil on the 4th! Yay!

    juliemama wrote on June 23rd, 2011
  28. As a New Englander i have now decided what i am doing this weekend. I loved those days at the Beach collecting Mussels and then Clams on the intercoastal clam beds. Or maybe i will just go to Newicks Restaurant

    bradley wrote on June 23rd, 2011
  29. I would buy them all more often if I only knew how to cook them.
    Gulping down raw oysters is not something I will be doing anytime soon…yuck.

    Wish there would be more frogs and wood snails available in the States…haven’t been able to find any of those except in restaurants I can’t afford.

    Primal Palate wrote on June 23rd, 2011
  30. I can’t choose just one kind of shellfish, I love them all. My SO made me a bloody mary with jumbo shrimp garnish once, that was good. I recently tried mussels for the first time, they taste like a cross between oysters and clams(whats not to like?)

    bbuddha wrote on June 23rd, 2011
  31. Now I’m Hungry! Great post.

    Scott wrote on June 23rd, 2011
  32. I’ve heard advice on avoiding ‘bottom feeders’ (e.g. catfish, mussels, bivalves, etc) because they would tend accumulate a greater quantity of toxins due to the nature of their diet (heard similar reasoning regarding pork). Anyone think there is any merit to this?

    Splat wrote on June 23rd, 2011
  33. Hi Mark,

    Do you have any data on how much vitamin K2 the various shellfish contain?


    Alex wrote on June 23rd, 2011
  34. I love Oysters, Mussels, and Clams. Don’t really like the crayfish, I just can’t eat anything that’s looking at me.

    Tatianna wrote on June 23rd, 2011
  35. Shells aren’t exoskeletons, they’re shells! Exoskeletons are chitinous enclosures that support the structure of the arthropod invertebrate and its segmented legs, which allow it to move. Shells are calcified structures that protect the bivalve or other mollusk, in fact often hindering their ability to move.

    cTo wrote on June 23rd, 2011
  36. I’m drooling all over the keyboard, thanks Mark!!

    I haven’t tried all these, except for mussels (albeit from my pre-prepared meal days 😛 ), shrimp, & crab.

    There’s something about seafood that feels incredibly right!

    I remember when I used to find it repulsive; oh me 😀

    Dave wrote on June 23rd, 2011
  37. In truth most of these make me a little squeamish. I can gut a deer but let an oyster slide down my throat? I think not. I haven’t eaten oysters or smoked clams since I gave up crackers. I’m not sure how to eat them now. The crackers were the only thing that made them go down. As for lobster – good, yes, although I’m not a fan of cooking a live one myself. I used to like shrimp more than I do now – ever since I couldn’t stomach shrimp when I was pregnant my taste for them has not been the same.

    Dawn wrote on June 23rd, 2011
  38. Benji wrote on June 23rd, 2011
  39. Sure… look what you did. Reading this at 6AM and now crave mussels.They will definitely be on the supper menu.

    Two pounds of steamed mussels are delicious. The left over broth I put in a mug and drink hot like coffee. Priceless!

    George wrote on June 24th, 2011

Leave a Reply

If you'd like to add an avatar to all of your comments click here!

© 2016 Mark's Daily Apple

Subscribe to the Newsletter and Get a Free Copy
of Mark Sisson's Fitness eBook and more!