Crab © Queensland Museum, Neville Coleman Collection

Fascinating crustaceans

Did you know that crabs have blue blood? Join Dr Marissa McNamara, Collection Manager of Crustacea for episode 4 of the Museum Revealed podcast.

Meet our guest

Dr Marissa McNamara is a Collection Manager working with the crustacean collection. She spends her time with jars of crabs and lobsters and boxes of barnacles, making sure the 50,000 or so registered specimens are in good condition. She also registers new crustacean specimens into the State Collection, helps researchers borrow specimens, and answers public enquiries such as, “What crab did I find on the beach?”

Read Marissa's profile

What are crustaceans?

Crustaceans belong to a subphylum of the Arthropoda, and are among the most successful animal groups with almost 52,000 described species. They are as abundant in the oceans as insects are on land. It is estimated that the tiny marine copepod crustaceans make up over half of all animals in the world by sheer numbers, and krill (the preferred food of some types of whales) has one of the greatest biomasses on the planet. As such, crustaceans are a crucial component of most marine food webs.

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In case you prefer to read

RB: Welcome to the Museum Revealed podcast brought to you by the Queensland Museum. Join me, Dr Rob Bell (RB), as we chat to the people that make museums so fascinating from curators, scientists and researchers. Dive deep into conversations with these storytellers that inspire us to be curious about our past, make sense of the present. And, of course, help us consider the future. Right now, we’re joined by Dr. Marissa McNamara (MM), who is the Collection Manager of Crustacea. So I’m going to start by asking you if you can sort of define what Crustacea is or what’s a crustacean, but what groups does it include and maybe what it doesn’t, but people might think it does.

MM: Yeah, there’s a great question. So crustaceans include familiar animals like shrimps, lobsters, fronds and crabs. But they also include less familiar animals like barnacles.

RB: So a barnacle is in the same group – there you go, I’ve learned something new. I mean, a barnacles in the same group as a lobster.

MM: That’s correct. Yeah. So it’s subphylum, they are arthropods. There are crustaceans are in the phylum arthropoda, but it’s some phylum crustacea. And you’re not alone in being uncertain about barnacles because people for a long time didn’t know what group barnacles were part of.

RB: So were barnacles homeless or did they belong to a different group?

MM: Well, some people assigned them to like molluscs because, you know, they look like they know they have a shell. Right. And people even in the Middle Ages thought that geese hatched from barnacles. So there’s been a lot of confusion about barnacles over the years. But, yeah, they’re hidden underneath those valves. But actually, the animal inside looks like a tiny little shrimp that’s cemented by its head and its feet are used to feed. So when the valves open up, they stick their feathery feet out and they pick up particles of food from the water.

RB: Fascinating. I didn’t realise. I always thought barnacles were just a nuisance, but now I find out there are fascinating.

MM: Yeah, they are quite interesting and there’s different groups of barnacles. So those barnacles that people associated with geese are in a group called the Goose Barnacles because they are on a stalk. So you have the acorn barnacles that are like little volcano looking things on rocks. And then you have the goose barnacles and they’re really they look like aliens. They have some very cool specimens at the museum that you hold up a jar. And it just looks like this bizarre thing on a stalk.

RB: Thanks. Well, speaking of the museum collection, can you talk us through, I guess, some of the other things that you’ve got in the collection? And I guess how many?

MM: Yeah. So the crustacean collection, we have over 50000 registered lots. So quite a few specimens. There’s 23 rows in the compactus and in the wet store and there’s a whole range of wonderful creatures that I get to see. So actually barnacles are at the beginning of the first row of the crustacean section is barnacles. And then we move on to things like shrimps, crabs, of course, lobsters. One really fascinating group is this stomatopods, the mantis shrimp. Okay. So they’re one of my favourites.

RB: Yes. Yes. I want to talk more about them as well. I think I’m also quite fascinated by by mantis shrimp. How do you how do you keep a crustacean? Like, I’m just thinking of myself familiar with crabs, lobsters and prawns. Definitely. The insides obviously wouldn’t preserve particularly well dried out, I imagine, although the outsides would. So do you sometimes just keep a shell or you would talk about the wet stories that we have sort of stored within alcohol or something?

MM: Yeah, so that’s a great question. So at the museum, just in general, different collections have different proportions in ethanol and dried. So for the crustaceans, about 90 percent of the collection is wet, is in ethanol. So most of the time, if we have a crab or a lobster or whatever, we just put it into a jar and fill it up with ethanol. We don’t have to fix it first for some large things like fish. They actually have to be fixed with formalin before they go into ethanol. But for most of the crustaceans, because they’re small enough, we can just put them straight into ethanol. So when you think of the crustacean collection, you’re actually what it is, is jars and jars filled with ethanol, with crabs and lobsters and wonderful creatures.

MM: So do they. I guess what I’m trying to say is, do they retain their color in the jars of alcohol and the color that we often associate with crabs and lobsters being bright red and orange. That’s not necessarily the color that they are in the environment anyway. So can you maybe talk us through, I suppose, how we have to get that red color? Where that comes from? And what sort of colourations might be preserved in your collection, whether it be dried.

MM: Right. So let me just I think we’re you’re talking about the red color. That’s, I think the famous thing with. Lobsters, right? When they’re like boiled, I suppose I’m ready at the restaurant. And so that that’s just because it’s been boiled, right. They’re not right. The American lobsters aren’t that bright red color. But in terms of the colour of the specimens in ethanol, they do lose colour over time. But like, I just had a little T-Rex crayfish specimen with a very cute orange fingertip. So it’s one of the common species around Brisbane that someone had collected and brought in. So I’ve put that into ethanol and it’s been a couple of weeks and I can still see the color of the orange tips of the claws. So I’m not sure exactly how long it will take for it to fade, but eventually they do fade. But you can still see some of the beautiful patterns on them, which is really cool. I was just actually taking out some specimens of this reef crab that has a really striking appearance. Beautiful orange color in life. And so you couldn’t see that in the jar, but you could still see the pattern on the back of it, which was cool. But in terms of coloration, in general, you get a huge range of color depending on the crustacean in life. I mean, everything under the sun, mantis shrimps, again, because they’re so cool. The peacock mantis shrimp has this amazing green and red and striking coloration on it. So, yeah, you get a whole variety.

RB: Excellent. You mentioned crabs there briefly. And I suppose not just the crabs maybe, but across crustaceans again. Are they poisonous? Well, might be venomous is a better question. Are they venomous crustaceans?

MM: So. Okay, first of all, difference between poisonous and venomous. Yes. So venomous is the creature injects the toxin into you, whereas poisonous is passive. So you have to eat it. So, yes, there are poisonous reef crabs they’re also called black fingered crabs. And they’re often very brightly colored, but they can be extremely toxic. So one species that is found off the Queensland coast was found to have enough toxin to kill 40,000 people because it was so concentrated.But it’s actually a bit of a mystery how those crabs get the toxin in them. They’re mostly scavengers, those species. And it might be that they are eating like toxic algae. But it is it’s a bit of a mystery. There’s still research being done on to the source because it doesn’t seem to be something the crabs generating themselves. But, um. Yes. So people have died, especially in island nations, by eating, you know, catching a crab from the reef and eating it. And it’s their last meal. So definitely we say if you don’t know what the crab is, don’t eat it, especially if it’s from a coral reef somewhere.

RB: Stick around as we find out more about mantis shrimp and possibly a little bit about krill and blue blood.

RB: Welcome back to the Museum Revealed a podcast. We are chatting with Dr Marissa McNamara. I mean, we’re talking about crustaceans and we’re going to dive right now into, I think, Marissa’s favorite crustacean, the mantis shrimp. Can you tell me about the mantis shrimp and why they’re so amazing?

MM: Gladly. So mantis shrimp are these incredible predators. They strike with the speed of a bullet. So there’s two groups of mantis shrimp based on how they feed. There are spears and smashers. So the spears have a sort of serrated, knife shaped reportorial limb that they use. They strike with it and they can spear soft body prey like fish. And then the smashers have a club shaped, wrapped limb that they use to smash things like shells or crustaceans. They have an incredible coloration. They also have incredibly sophisticated vision. So they have the most complex vision in the animal kingdom. So whereas humans have three cones in our eyes to see the colors that we see, mantis shrimp have 12. So they can see ultraviolet light and polarized light. They just have this amazing vision. They’ve been called shrimp from Mars. And researchers don’t even know exactly why they have such complex vision. They think it might be related to mating signals or obviously, you know, some sort of communication. But it’s still a bit of a mystery, which is really so cool that we don’t know everything yet. Mantis shrimp vision has actually been used in some research applications. So some researchers have used the way that the cells, the cells and mantis shrimp eyes are aligned like a 45-degree angle. And there were, as a group of researchers who made a bio inspired camera by stacking the camera elements at the same 45-degree angle. And that camera has been used like in cancer detection, because it can detect things, I guess, better than other cameras. And mantis shrimp vision has also been used to help develop technology for self-driving cars. I mean, you never know what applications research will have. I mean, who would have thought that some crustacean I would end up being used one of the cars.

RB: The most complicated eyes in the animal kingdom. Yeah. And it’s probably quite hard to imagine what it looks like through a mantis shrimp’s eyes when you can only see through our eyes. And, you know, we think we can see the rainbow of colors, unlike you know, dogs. We might not be able to see that particular color. Yeah. So it’s obviously impossible for dogs to know what we can see with that extra color. Yeah. But to even wrap your head around what a mantis shrimp must see.

MM: I would love to be able to see through mantis shrimps eyes. I mean, if you see a video clip of them, even like the eyes just have this amazing appearance and they’re both moving independently and they just look so cool.

RB: In case anyone out there is now afraid to go in the water because mantis shrimp they what they speak as they collapse. How big is a mantis shrimp?

MM: They, they range in size. Quite a few of them are maybe about 10, 15 centimetres but they can get quite big. We have one specimen at the museum that is in this big jar and maybe it’s about 20 centimetres, but smaller than lobsters. So, yeah. And it’s a very cool creature. So they can they can reach a decent size.

RB:Now, I’ve also heard, this could be a myth, so let me know. Have they been known to break an aquarium?

MM: Yes, I, I believe that is true. I wouldn’t I wouldn’t be surprised based on what they can do. I’ve tried to find actually, you know, a video showing yet, which they did. But I know that they do strike with incredible force, though. So I think that is every chance they could, correct?

RB: Yes. OK. So if you’re going to collect mantis shrimp, make sure you’ve got strong glass polycarbonate or something they can’t get through. Now I also want to know about a species It’s probably not thought about very much, but are probably massively abundant, and that’s krill. What can you tell us about those little things?

MM: So krill are crustaceans. They look like tiny shrimp and they feed on phytoplankton, single celled plants in the ocean. And they play an important role in the marine food chain because lots of other animals feed upon crewel like birds and whales. And yeah. So they’re small, but they’re incredibly important.

RB: And so it is sort of the start of the food chain for a lot of things in the ocean. Now, moving on to probably a favourite area of mine when it comes to crustaceans, except maybe mantis shrimp as they are now my favourite too. But crabs, because I think there’s lots of cool things about crabs. One is there’s a couple of particular crabs that I’ve read about. The first is a spider crab, or maybe it was the Japanese spider crab. Do you know much about them?

MM: Yeah. So they’re one of the largest crabs in the world. So the question of largest crab actually kind of comes down to how you want to define it. So the spider crabs are the largest in terms of leg span

RB: I would have guessed that from the name. How big do they grow?

MM: Yep. So the Japanese spider crab can actually reach 3.7 metres across its leg span. It’s some of the largest of any arthropods.

RB: enormous. You wouldn’t want to run into one of those. That sounds like something out of a Harry Potter films.

MM: It does. It’s huge. But one of the other largest crab species that we have in Australia is the giant crab found off Tasmanian waters. That one doesn’t get quite so big in terms of the leg span, but it can be quite massively heavy and it can reach 14 kilograms and has a claw that can reach the size of a human forearm. So they’re very cool. We have a dry specimen at the museum and also just a claw at the museum that I often bring out at events. And it’s the males that have that oversized claw that reaches that size. So the females have two claws that are the same size. And there’s actually a fishery for the giant crabs off the southern waters of Australia. But they have to manage the fishery because they’re are a deep water, slow growing species. The giant crab. So, yeah, if they’re if they’re overfished, they won’t be able to recover, recover yet.

RB: And so are you saying the males have. Is it just one big claw.

MM: So the males have one oversize claw and then the one claw that’s smaller.

RB: Is that a little bit like for the little fiddler guys you see running around the crab? So one oversize claws. Well, they sort of hold up. That’s right. I mean, and that’s really, you know, wrestling other males and whatnot.

MM: So that’s exactly right. There’s lots of really cool fiddler crab species even in Morton Bay. There’s one species, the lemon fiddler that has like it can be like a black and white stripe or like this incredible black and white modeling in this yellow claw. And it looks like something out of a painting by someone who was on drugs or something.

RB: Something I found kind of fun, not that I’ve done it on purpose, but I’ve sometimes led us to fiddler crab scuttles down the nearest hole. And it’s not it’s hole it it’ll sometimes they get chased out.

MM: But it’s amazing because you know, if you walk down there, they all disappear. They’re so quick. Because I mean we’ve tried to catch them.

RB: The last thing I want to chat about is something that a lot of people might not know about crustaceans. They’ve got different blood, I suppose, to a lot of the rest of us mammals anyway. Tell me what you know about their blood.

MM: Yeah. Well, that’s right. So we humans, we have red blood because hemoglobin is the protein that binds oxygen and crustaceans use a different copper based protein called hemosiderin. So it does give the blood a bluish color, which is pretty cool.

RB: So there was royalty in a way. Can either of us aspire to be is as great as a crab? So do we think that’s just that’s just an evolutionary quirk means that we have on that sort of helps bind our blood oxygen. I just happen to have copper. Maybe it’s more abundant in the ocean. I’m not sure what to do. I’ve no idea. Do you have any idea where this comes from? Do you?

MM: That’s a very good question. I there are other organisms that use, I think it’s some worms. There’s a different compound as well that they use. So it may just be, you know, we’re human centric. So we think hemoglobin is the best sign and seems to work as well.

RB: But obviously they are pretty abundant. You have 50 odd thousand in your collections. Yes, there’s plenty around.

MM: And speaking of blood, there’s another interesting thing with horseshoe crabs. Now, horseshoe crabs are not actually crabs. They’re not crustaceans. They’ve got that common name, though, because of their appearance, they are, strange, very prehistoric looking creatures. So their blood has this really fascinating property where they have compounds in it that will latch on to any foreign invaders like bacteria. And so horseshoe crabs are actually harvested by the thousands, by pharmaceutical companies that extract their blood to be used in like chemical assays to detect the presence of bacteria and things.

RB: So horseshoe crab, even though they are not a crab, their blood is used to detect like bacteria in lab tests.

MM: Yeah. And some in some tests. Yeah. So it’s another sort of fascinating thing in the natural world. Even though they’re not crustacean, they have the name crabs. So I can talk about it’s true.

RB: It’s been fascinating. Thanks so much for joining us. I certainly learned a lot. I hope you’ve learned a lot as well. Thanks for joining us on the Museum Revealed podcast. What did you uncover this episode? If you’re interested in learning more than follow the Queensland Museum on Social Media, it’s @Queensland Museum. Or head to our website, and you can sign up for the E-news list so you can keep up to date with everything and there’ll be show notes to go along with this. So you can delve a little bit deeper into some of the things we’ve talked about. Until next time. Stay curious.

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