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Movin’ On Up: Hermit Crabs & the World’s Only Beachfront Social Housing

(Via: )
(Via: onestopcountrypet.com)

Common Name: The Hermit Crab

A.K.A.: Superfamily Paguroidea

Vital Stats:

  • There are around 1100 species of hermit crabs in 120 genera
  • Range in size from only a few millimetres to half a foot in length
  • Some larger species can live for up to 70 years
  • Most species are aquatic, although there are some tropical terrestrial species

Found: Generally throughout the temperate and tropical oceans, in both shallow and deep areas (I was unable to find more specific data on this.)

Trop. & Temp. Oceans

It Does What?!

If there’s one thing nature loves, it’s symmetry. Sometimes radial symmetry, as we see in starfish or sea anemones; sometimes bilateral symmetry, as in mammals and insects, which have a right half and a left half. External asymmetry is extremely rare in living organisms, and when it does occur, it is generally in a minor form, such as a bird species with beaks bent to the side, or a type of flower with oddly distributed stamens. One of the very few groups with entire bodies that lack symmetry are the gastropods; specifically, the snails. They develop helical shells with asymmetrical bodies to match.

caption (Via: Wikimedia Commons)
The shells also hide how ridiculous they look naked.
(Via: Wikimedia Commons)

But this post isn’t about snails. It’s one thing to evolve an unusual asymmetrical bodyplan to go with your asymmetrical home. It’s another to evolve an asymmetrical bodyplan to go with somebody else’s home. Which brings us to the hermit crab. When snails die in ways that leave behind perfectly good shells on the beach, these guys literally queue up for the chance to move in. Hermit crabs are part of the decapod order of crustaceans, as crabs are, but are not in fact true crabs, and unlike most other crustaceans, they lack any kind of hard, calcified plating on their abdomens (think shrimp shells). Instead, they have a soft, spirally curved lower body that fits perfectly into a snail shell, with muscles that allow them to clasp onto the interior of the shell. Paleobiologists have found that hermit crabs have been living in found shells for over 150 million years, and that they made the move to snail shells when their original shell-producer, the ammonite, went extinct. Living in shells has strongly restricted their morphological evolution, meaning the crabs of aeons ago look pretty similar to the crabs of today, because their housing situation doesn’t allow a lot of change.

caption (Via: Telegraph.co.uk)
Housing shortages hurt everyone.
(Via: Telegraph.co.uk)

Back to those line-ups I mentioned. Unoccupied snail shells are a limited resource, and an unarmoured crustacean is an easy lunch, so of course a lot of fighting goes on over them; crabs will actually gang up on an individual with a higher quality shell and just yank the poor bugger out. But it actually gets much more complex than that… these little pseudo-crabs aren’t as dim and thuggish as you might think. You see, as a hermit crab grows over the course of its life, it needs a series of progressively larger shells in which to live. A crab stuck in an undersized shell is stunted in its growth and is much more vulnerable to predation, since it can’t fully withdraw into its armour. The easiest way to find your next home? Locate a slightly larger hermit crab about to trade up and grab its shell afterward. This is how the crabs form what are called “vacancy chains.” A series of individuals will line themselves up in order of size (I’ve seen groups of schoolchildren unable to perform this task), waiting for hours sometimes, and as the largest crab moves to its new shell, each successive crab will enter the newly vacated one. Brilliant… new homes for everybody, and no one gets hurt. In fact, if a given crab chances upon a new shell that it judges to be too large for its current size, it will actually wait next to the shell for a larger crab to come along and a vacancy chain to form. That’s pretty impressive reasoning for a brain smaller than a pea.

[Fun Fact: Larger aquatic hermit crabs sometimes form symbiotic relationships with sea anemones; the anemone lives on the crab’s shell, protecting its host from predators with its deadly sting, while the crab shares its food with the gelatinous bodyguard.]

Today in Words You Didn’t Think Existed:
carcinisation / car·si·nə·ˈzā·shən / n.
a process by which an organism evolves from a non-crablike form into a crablike form.

That’s right, glossophiles, thanks to a British zoologist, we actually have a specific word for turning into a crab. English rules.

Says Who?

  • Angel (2000) J. of Experimental Marine Biology and Ecology 243: 169-184
  • Cunningham et al. (1992) Nature 355: 539-542
  • Fotheringham (1976) J. of Experimental Marine Biology and Ecology 23(3): 299-305
  • Rotjan et al. (2010) Behavioral Ecology 21(3): 639-646
  • Tricarico & Gherardi (2006) Behav. Ecol. Sociobiol. 60: 492-500
Say hello to my little friend. (Via: dailykos.com)
“Say hello to my little friend.”
(Via: dailykos.com)
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EVOLUTION TAG TEAM, Part 3: Coral Polyps & the Garden Within

The third in an ongoing series of biology’s greatest duos. (Check out Parts One and Two)

(Via: Wikimedia Commons)

Common Name: Coral Polyps

  • A.K.A.: Class Anthozoa, Subclass Hexacorallia

Common Name: Coral Algae

  • A.K.A.: Genus Symbiodinium

Vital Stats:

  • Polyps grow to a length of only a few centimetres, depending on species
  • Coral can grow outward at a rate of up to 10cm (4”) per year
  • The Great Barrier Reef stretches over 2000km (1243 mi) and can be seen from space

Found: Various coastal areas; largest reefs surrounding Australia, Oceania, and the Caribbean

It Does What?!

If you’ve ever been told that coral reefs are alive, then looked at one and felt a bit sceptical that this chuck of colourful rock could be a living thing… well, good for you, because you’re actually mostly right. The vast majority of the volume of a coral reef is, in fact, nonliving inorganic mineral (calcium carbonate, specifically). The amazing thing about coral isn’t so much what it’s made of, but what’s going on on the surface. You see, that oddly-shaped, porous rock is actually a communal exoskeleton produced and excreted over time by hundreds of thousands of polyps living in the tiny, cup-shaped depressions on the surface.

“Breaded, with a side of chips, please.”
(Via: Wikimedia Commons)

Looking like tiny jellyfish (and belonging to the same phylum), the polyps hide in the stony sanctuary they’ve made, letting only their tentacles project. These tentacles are tipped with stinging cells which can inject a powerful venom into any prey foolish enough to swim within reach. This prey can range in size from microscopic plankton to small fish. That’s right, coral eats fish. Watch where you stick your toes.

So where does the ‘duo’ part come in? Despite their ability to snatch passing sea creatures and eat them, coral polyps actually get only a small part of their caloric intake this way. Impressively, these guys managed to find a diet that requires even less effort than just reaching out and grabbing stuff. Who needs movement when you can just photosynthesize, like plants do? The polyps have developed a symbiosis with a type of single-celled alga (called zooxanthellae) that allows them to do just that.

The algae start out as free-living cells drifting through the water. They are eaten by the coral polyp, but instead of being digested, they are able to enter the cells lining its digestive tract. Since the polyps are transparent to begin with, all they have to do is expose their bodies to sunlight in order to allow the algae to produce sugars by photosynthesis (this is why reefs form in relatively shallow waters). The majority of the sugars made by the symbiont are then absorbed by the polyp.

And what do the algae get out of this arrangement? A couple of things. First, they get a safe place to live, and won’t get eaten by something that can digest them. Second, they get nutrients, in the form of carbon dioxide and nitrogen compounds, both natural waste products of the polyp’s metabolism. Still, sometimes as much as 30% of the cells in a polyp are algal cells, and this puts a stain on the host’s physiology.

“I’ve just got a lot going on right now.”
(Via: Wikimedia Commons)

Maybe you’ve heard of “coral bleaching” as one of the symptoms of pollution around reefs. Bleaching happens when additional stresses (like pollution) get to be a bit too much for the polyps to handle. They can’t change the water purity, so instead, they offload the stressor they can control- the algae. Getting rid of the photosynthetic cells also gets rid of much of the characteristic colour of the reef, hence the term ‘bleaching’. In the short term, this is a smart move. It increases the polyp’s chance of survival during brief crises, and new algae can always be taken on when the host is ready. The real problems start when the environmental stress persists, and the polyp never takes on new algae. Eventually, it can’t sustain itself and dies, as those in a tenth of the world’s reefs already have. At least there’s still hope for these areas; if conditions improve, new colonies can be formed using the old reef as a foundation. The Great Barrier Reef, for example, is considered to be between 6000 and 8000 years old. However, the modern structure has developed atop an older, dead reef system, thought to be over half a million years old. Time enough for us to clean up our act, maybe.

[Fun Fact: Coral polyps only reproduce sexually to start new colonies. Within a single piece of coral, all the polyps are genetically identical clones, produced by polyps dividing in half and then re-growing their lost tissues.]

Says Who?

  • CoRIS- Coral Reef Information System
  • Fransolet et al. (2012) Journal of Experimental Marine Biology and Ecology 420-421:1-7
  • Piper (2007) Extraordinary Animals. Greenwood Press: Westport, Connecticut.
  • Wooldridge (2010) BioEssays 32(7):615-625

    The little-known “Lady Gaga Coral”
    (Via: Wikimedia Commons)
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Thank a Horseshoe Crab

(Via: reefguide.org)

Common Name: Horseshoe Crab

A.K.A.: Family Limulidae

Vital Stats:

  • Four extant species of horseshoe crab in three genera (Limulus, Carcinoscorpius, and Tachypleus)
  • Females are larger than males, and can reach up to 60cm (24”) long in some species
  • Believed to live between 20 and 40 years

Found: Coastal waters of southeast Asia, Oceania, and eastern North America

It Does What?!

Like the platypus and the lungfish, horseshoe crabs are what biologists refer to as “living fossils,” meaning their basic form has gone essentially unchanged for many millions of years. In the case of horseshoe crabs, fossils as old as 445 million years have been found that are quite similar to the extant species of today.

Despite their common name, the Limulidae aren’t true crabs. They’re arthropods, like crabs, but are actually more closely related to spiders and scorpions. In fact, beneath that tough shell, they do look quite spider-like. If spiders had tails, that is.

Basically a tarantula in combat gear.
(Via: Wikimedia Commons)

Horseshoe crabs live in shallow coastal waters, feeding off worms and molluscs from the ocean floor. They are able to feed in near complete darkness at night due to a remarkable visual system. The creatures have three different types of eyes – compound, median, and rudimentary – located to both sides and to the front of their shell. What’s more, their compound eyes become a million times more sensitive to light at night than they are during the day. Since that’s roughly how much less light they have to work with at night, the crabs are able to see equally well at night and during the day.

Most people who have observed horseshoe crabs know them from their unusual breeding habits. Each spring and early summer, male crabs will search out a mate and attach themselves to the female’s shell using a special modified leg. Then, during the highest tides of the year, usually at night, the females crawl up onto shore by the hundreds, carrying their male cargo. Having picked a spot that’s moist, but not so low as to be washed away with the tide, they dig a nest into the sand and lay their eggs. The attached males get first dibs at fertilising the pre-laid eggs, but must share the task with numerous mate-less onlookers who rush in to get their shot at fatherhood as well (crabs are so uncouth). Since eggs number in the tens of thousands per female, many will probably be successful. Most of these thousands of eggs, however, will become food for migratory birds, who appreciate the extra protein snack on their long journeys. After a month or so, the uneaten eggs will hatch into larvae, which remain on the beach in groups for a couple of weeks before moulting into juvenile horseshoe crabs and finally moving into the water.

Horseshoe crabs, making more horseshoe crabs.
(Via: Wikimedia Commons)

Now you might be thinking, “That’s all well and good, but what can horseshoe crabs do for me?” Well, as it turns out, these creatures are some of the most prolific blood donors on Earth (whether they like it or not). Like our friend Mr. Spock, horseshoe crabs have copper-based blood, rather than the iron-based concoction favoured by humans. They are literally blue-blooded. And instead of white blood cells to fight off infection, they have amebocytes. These amebocytes are so valuable in detecting certain types of bacterial infections in humans that a quart of horseshoe crab blood is worth approximately $15,000 US. Crabs are caught, transported to a lab, and drained of about 30% of their blood before being released. The company behind this 50 million dollar per year industry states that only about 3% of the quarter million crabs die from the procedure annually, while other studies have found the number to be nearer to 15% (read more about it here). Knowing who’s right may become very important, as horseshoe crab populations are declining worldwide, additionally affecting the migratory birds that feed on their eggs. Either way, next time you survive an E. coli infection, thank a horseshoe crab.

No, no… we don’t mind. Really.
(Via: TYWKIWDBI)

[Fun Fact: Horseshoe crabs are thought to be the closest living relative of the extinct trilobite.]

[Also, here’s a cool video of (who else?) Sir David Attenborough explaining the mating habits of horseshoe crabs.]

Says Who?

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Anglerfish: Absorbing Ladies and their Freeloading Mates

(Via: Inglestic)

Common Name: Anglerfish

A.K.A.: Order Lophiiformes

Vital Stats:

  • Comprised of 322 species in 18 different families
  • Most range in size from that of a ping pong ball to that of a football
  • Some can reach over a metre in length and weigh 27kg (59lbs.)

Found: Throughout the world’s oceans, mostly in deeper regions

It Does What?!

The more dissimilar a creature’s habitat is to our own, the more dissimilar we have to expect its lifestyle to be, so when we plumb the pitch black, cold, high pressure depths of the ocean, we’re counting on some serious weirdness. The anglerfish goes above and beyond in this department.

First off, have you seen these things? They’re essentially a set of mobile fangs. And what’s with that thing hanging down off their heads? It’s all part of an efficient setup that allows the anglerfish to survive in an environment with minimal light and sparse prey. These fish are what biologists call “sit and wait” predators. In order to avoid expending precious energy, they hang motionless in the water, waiting for something edible and foolish to approach. The dangly piece is actually a lure, filled with bioluminescent (glowing) bacteria. Seeing the glow and thinking it might be food, curious creatures draw near and are quickly gobbled up by the anglerfish. That enormous mouth, combined with a flexible bone structure, allows the fish to swallow very large prey, relative to its own size.

Really… how unobservant must their prey be?
(Via: National Geographic)

Amazingly, the anglerfish’s horrifying appearance isn’t its most notably odd trait. Not even close. You see, all these characteristics we’ve discussed so far are only present in the female of the species. The male is a different creature entirely. Many times smaller than the female, you’d be hard pressed to immediately recognise a male anglerfish as even being part of the same species. In fact, researchers initially thought they were babies. Their adult form is only 6-10mm (0.24-0.39”) long in some species, placing male anglerfish among the smallest vertebrates on earth.

What’s more, they don’t have a functional digestive system… they literally don’t ever eat. Sustained only by the energy in his own tissues, the young male must find a female and mate before he starves to death. To aid in his quest, he has very well-developed eyes and huge nostrils, which allow him to follow the pheromone trail of a potential mate.

The somewhat less intimidating male anglerfish.
(Via: Anglerfish Info)

Now it gets weird. Upon locating a female, the male swims up and latches on to her with his teeth, usually on the lower side of her body. He then starts to release an enzyme which dissolves both his mouth and her skin, right down to their respective blood supplies. Soon, their bodies actually fuse together, and blood from the female begins to nourish the now-parasitic male. In some species, this fusion goes all the way to the base of the male’s skull, giving him the appearance of having his entire head absorbed into his mate’s body. Once fused, the male undergoes a growth spurt, thanks to his new food source, but his internal organs, as well as his eyes and nostrils, degenerate and atrophy. The exception, of course, being his testicles, which grow along with the rest of his outer body.

A female anglerfish and her clingy boyfriend.
(Via: Wikimedia Commons)

Her mate degenerated down to a mere sperm-producing external organ, the female anglerfish is now essentially a self-fertilizing hermaphrodite. With anywhere between one and eight males attached to her, she has an abundant supply of sperm available whenever she has ripe eggs to be fertilized. As for the males, they will “live” for as long as the female lives, and continue to reproduce indefinitely.

[Fun Fact: the species Ceratias holboelli has the most extreme size difference between the sexes. Females are more than 60 times the length and about half a million times heavier than the males.]

[And if you like your science lessons in cartoon form, be sure to check out this out.]

Says Who?

Come to Mama!
(Via: fugly.com)
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How to Stay Cool the Lungfish Way

Via: Science News for Kids

Common Name: The Lungfish

A.K.A.: Subclass Dipnoi

Vital Stats:

  • 6 species; 4 in Africa, 1 in South America, 1 in Australia
  • Some species can reach up to 2m (6.6’) long and weigh 43kg (95lbs.)
  • Omnivorous, eating plants, insects, crustaceans, worms, fish, and frogs
  • Largest genome of all terrestrial vertebrates at ~133 billion base pairs

Found: Slow-moving freshwater bodies in South America, Africa, and Australia

It Does What?!

Well, they’re not much to look at, but in the “quietly carrying on while everything drops dead around you” department, the lungfishes are tops. These large, eel-looking creatures are what biologists refer to as “living fossils”, species which have existed in more or less their present form for a very, very long time. In the case of the lungfishes, around 400 million years. For the sake of comparison, this was around the same period that plants developed roots and leaves. That long ago. In fact, researchers believe that the lungfishes are the closest living relatives of the terrestrial vertebrates (that is, anything with a spinal column that lives on land).

These will probably outlast humanity.
Via: One More Generation

So what makes these things so interesting, besides being old? First off, they breathe air, as you might have guessed from their name. Australian lungfishes have a single lung, and, while they normally breathe through their gills, are able to supplement their oxygen intake with air during times of high exertion or when their water gets stale (Fun side note: During mating, Australian lungfishes make loud burping noises at the surface of the water which are thought to be part of the courtship ritual. I’ll refrain from making any Aussie jokes here… ). African and South American lungfishes, on the other hand, have two lungs and breathe nothing but air. Their gills are completely atrophied, such that they could actually drown if kept under for much longer than their usual 5-8 minutes between breaths.

“Hey! I’m trying to aestivate in here!”
Photo by: Tobias Musschoot

This ability to breathe without water results in the other fantastic ability of subclass Dipnoi. South American and African lungfish live in habitats which often dry up completely during the hottest part of the year. The fishes’ gross but brilliant answer to this is to burrow up to half a metre down into the soft mud and excrete a huge amount of mucous. As the surrounding mud dries up, the mucous forms a hard shell which keeps the curled up lungfish moist and cool. A small hole at the top of this snot-cocoon allows the fish to breathe. It’s metabolism slowed to only a small fraction of the normal rate, the creature will aestivate (like ‘hibernate’, but without the cold) like this for several months until the rains return. Laboratory experiments have shown that an African lungfish can remain alive under these conditions for as long as six years.

“Granddad”: probably older than your Granddad
Via: Shedd Aquarium

Aside from their amazing survival abilities, these fish have unusual lives, as fish go. They are extraordinarily long-lived. The Shedd Aquarium in Chicago holds an Australian lungfish known as “Granddad” which arrived there as an adult in 1933, making him at least 80 years old. Females of this species don’t even mate until they’re at least 22 years old (or so they tell their parents). What’s more, some species actually care for their young. The mother and father build an underwater nest for their offspring, which can only breathe via their semi-atrophied gills for the first seven weeks, and the father uses his body to release additional oxygen into the surrounding water, helping them to breathe. So, dual childcare: not such a new idea after all.

[Extra Credit –  Here’s a short video of a lungfish being stalked by a pelican. Spoiler: It ends badly for the lungfish.]

Says Who?

  • Brinkmann et al. (2004) Journal of Molecular Evolution 59: 834-848
  • Fishman et al. (1992) Proceedings of the American Philosophical Society 136(1): 61-72
  • Glass (2008) Respiratory Physiology & Neurobiology 160: 18-20
  • Joss (2006) General and Comparative Endocrinology 148: 285-289
  • Lee et al. (2006) General and Comparative Endocrinology 148: 306-314
  • www.fishbase.org
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What’s the matter, louse got your tongue? (Cymothoa exigua)

Via: Parasite of the Day

Common Name: The Tongue-Eating Louse

A.K.A.: Cymothoa exigua

Vital Stats:

  • Females are 8-29mm long by 4-14mm wide (0.3”-1.1” x 0.16”-0.55”)
  • Males are 7.5-15mm long by 3-7mm wide (0.3-0.6” x 0.12”-0.28”)
  • Preys on 8 species of fish from 4 different families

Found: In the Eastern Pacific, between the Southern U.S. and Ecuador

It Does What?!

With a name like “Tongue-Eating Louse”, you know this is going to be viscerally horrible, but bear with me… it’s also pretty neat. Despite the name, these aren’t actually lice, but parasitic crustaceans known as isopods. While there are dozens of species in the genus Cymothoa, most are parasites which live in the gills of fish and are, relatively speaking, unremarkable. But Cymothoa exigua is something special. While the male of the species (and this is a slippery term, as they can change sex when necessary) lives in fish gills, the female has developed an altogether original strategy.

Try to enjoy a tuna sandwich now.
Via: Smithsonian.com

Entering through the gills, the female takes up a position at the back of the fish’s mouth and attaches herself to the base of its tongue. She then pierces the tongue with her front appendages and begins to consume the blood inside it. Over time, the lack of bloodflow causes the tongue to slowly wither up and fall off. What’s left is a stump consisting of about 10% of the original tongue (yes, someone measured this). The parasite can now attach herself to the stump using her seven pairs of hook-like pereopods (read: ‘feet’) and actually begin to function as the fish’s tongue.

What’s really amazing is how well this seems to work. The parasite has evolved a body shape which closely matches the curves of the inside of the host’s mouth. Unlike our tongues, a fish tongue has no real musculature or flexibility; its only real function is to hold food against the fish’s teeth. With the parasite in place, the host is able to use its body to do exactly that. While the isopod is thought to feed on the fish’s blood, researchers have found that infected hosts have normal body weights and typical amounts of food in their digestive tract when caught. This is, to date, the only known case of a parasite functionally replacing an organ in its animal host.

Once it’s in there, this thing’s not coming out without a fight.
Via: This Site

Because edible snapper fish are amongst the host species of C. exigua, there have been cases of the parasite showing up in people’s supermarket purchases, including one person who thought they had been poisoned after eating one. So are they dangerous? Not to eat, no, but researchers tell us they can give a nasty little bite, given the opportunity. So the moral of this story is: if you bring home a fish for dinner and see an evil-looking parasite posing as its tongue… don’t stick your finger in its mouth.

.

Says Who?

  • Brusca & Gilligan (1983) Copeia 3: 813-816
  • Brusca (1981) Zoological Journal of the Linnean Society 73(2): 117-199
  • Williams & Bunkly-Williams (2003) Noticias de Galapagos 62: 21-23
See you in your nightmares.
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Sea Cucumbers, or, How to Really Lose Weight Fast

Via: www.starfish.ch

Common Name: Sea Cucumbers, Holothurians

A.K.A.: Class Holothuroidea

Vital Stats:

  • Approximately 1250 species
  • Size: 2-200cm (¾” to 6.5’)
  • Lifespan: 5-10 years in the wild

Found: Throughout the oceans, in both shallow and very deep regions

It Does What?!

Where to begin? This is an odd one… To start, despite the name sea cucumber, this isn’t a plant but an animal; a relative of starfish and sea urchins. One could be forgiven for mistaking the holothurians for plants, however. Most spend their lives lying on the ocean floor, looking like a sunken vegetable, and covering a distance of a couple metres or less per day in their search for food. The creatures feed on small particles, like algae and plankton. There is a tiny mouth at one end of their body, surrounded by between eight and thirty tentacle-like feet with which they grab their food and which can actually be retracted into their mouth. But that’s not really the interesting end of a sea cucumber, as we’ll see.

Via: www.answers.com

Lacking both eyes and any rapid means of locomotion, holothurians are tempting prey for crabs, fish, and other large sea creatures. When threatened, they have the single most bizarre and seemingly impractical defence mechanism ever evolved: self-evisceration. As a predator approaches, the sea cucumber violently contracts the muscles around its body wall and actually expels its own internal organs via its anus (demurely labelled as the ‘aboral pole’ in the diagram). Yes, really. In some species, these organs include most of the creature’s respiratory system, which takes the form of sticky threads that blanket and ensnare the predator. And just to add genuine injury to the insult, this discharge is accompanied by a toxic chemical known as holothurin, which kills whatever’s nearby. Disgusting, but effective. Once expelled, the missing organs can be regenerated in 1-5 weeks, depending on the species. Some researchers speculate that this ability may even be used as a means of ridding the organism of accumulated waste or parasites. The ultimate detox regime, if you will.

Are those your lungs, or are you just happy to see me?
Via: Wikimedia Commons

One such parasite is the pearl fish. You see, holothurians actually breathe through their rear end as well, so when one of them, umm… opens up… to take in some fresh, oxygenated water, in goes the fish, which then feeds on the sea cucumber’s internal organs. You can see why they might want to rid themselves of this visitor.

Strange as it all seems, the sea cucumber’s strategy is quite a successful one. At depths below five and a half miles (8.8km), they make up fully 90% of the mass of all macrofauna (i.e. any animal that’s not microscopic). Among the species that live at shallower depths, populations can reach a density of 1000 cucumbers per square metre. And it’s a good thing, because they’ve got one predator with whom spewing out their guts won’t work: humans. Sea cucumbers are a popular ingredient in Chinese and other Southeast Asian cuisines, although only about ten species are used for this purpose. These species are farmed commercially in artificial ponds, and are also used in traditional Chinese medicine. Perhaps not surprisingly, they are considered to improve male sexual health.

Does a Body Good.
Via: www.theworlds50best.com

[Fun fact: Sea cucumbers have a body wall made up of collagen fibres which they can ‘unhook’ at will, essentially liquefying their interiors and allowing them to squeeze into very small cavities as a means of hiding from predators. Once inside the cavity, they re-solidify themselves, making the creature very difficult to extract from its hideout.]

Says Who?

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If the Eyes are the Window to the Soul, this Fish has a Sunroof

Things are lookin’ up

Common Name: Barreleye Fish

A.K.A.: Macropinna microstoma  (and related species)

Vital Stats:

  • Size: 15cm (6″) long
  • Depth: 600-800m (2000′-2600′) below sea level
  • Discovered: 1939
  • First Photographed: 2008

Found: Subarctic and Temperate regions of the North Pacific

It Does What?!

As you have likely already noticed, fish don’t have necks. At least not in the sense that they are able to look upward. So for a bottom-dweller lurking about in the cold depths of the ocean, being able to see that tasty bit of food floating by above is something of a problem. Some species get around this issue by floating vertically in the water so their whole bodies are pointing upwards. Simple enough. But in the spirit of meeting every challenge with an impossibly bizarre solution, nature has also produced a fish with eyes directly on the top of its head. After all, why re-orient the entire fish when you can just shift a couple of parts?

Those things on the front that look like eye sockets?
That would be its nose.

But the strangeness of the Barreleye Fish goes a little further than that. These aren’t just normal fish eyes in an unusual location. This species’ main prey are jellyfish and their relatives, which frequently come equipped with stingers that could damage the eyes of most predators. So rather than a normal spherical eye perched on top of its head, Macropinna has a tubular structure with the lens buried deep within its head (the dark green areas in the images). Overlying the tubular eyes is a tough, fluid-filled, transparent shield which the fish can look through. That’s right, it looks through the top of its own head. This way, stings from jellyfish will never damage the delicate ocular tissue.

What’s more, the fish’s unique tubular eyes are supremely adapted for the dark depths of the ocean. They allow unusually accurate depth perception (due to a large overlap of the two visual fields) and enhanced light gathering compared the spheroid eyes. In an environment up to 2600 feet (800m) down, where little daylight penetrates and everything appears in monochrome, these adaptations enable the barreleye to distinguish even faint shadows and silhouettes moving above it, and to precisely gauge how far up they are.

The Barreleye Fish, failing to look at the camera.

Researchers had long been puzzled as to how the barreleye eats, since, with its eyes on top of its head, its visual field didn’t include the area around its mouth. The species has been known since 1939, but only as small mangled bodies caught up in deep-sea fishing nets (adults are only about six inches long). In each case, the transparent casing of the fish’s head had been destroyed by the nets and the rapid changes in pressure as the nets were pulled up, making its anatomy difficult to study. In 2008, however, scientists from the Monterey Bay Aquarium Research Institute sent remote operated vehicles with cameras down to try, for the very first time, to snap some photos of these oddballs in action. What they learned was that, when it spots prey, the barreleye can actually rotate its entire tubular eye downward, like moving the telescope in an observatory. This way, it can turn and look at its target straight on as it pursues. Most of the time, though, the fish was seen to use its large, flat fins to hold itself nearly motionless, looking up through its personal sunroof, just waiting for some unlucky jellyfish to float on by.

Says Who?

  • Robison & Reisenbichler (2008) Copeia 4: 780-784.
  • Monterey Bay Aquarium Research Institute

All images taken by the Monterey Bay Aquarium Research Institute (MBARI)

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A Shellfish Goes to the Dark Side (Sacculina carcini)

The crab barnacle, hitchin’ a ride.
(Image by Hans Hillewaert)

Common Name: Crab Barnacle, or the charmingly descriptive Dutch term “krabbenzakje,” meaning “crab bag”

A.K.A.: Sacculina carcini (and other Sacculina species)

Found: In the coastal waters of Europe and North Africa

It Does What?!

Most barnacles, those almost quaint crusts seen decorating old piers and ships, live their lives by cementing themselves to a hard underwater surface and using their arm-like limbs to pull passing bits of food into their mouths all day. Not so for the crab barnacle, who decided that all that arm-waving was for chumps and set about evolving into the ultimate free-loader.

Normal, hardworking barnacles, for the sake of comparison…
(Image by Michael Maggs)

In its immature larval form, Sacculina has a similar body plan to other barnacles and is able to swim about freely; however, rather than finding a surface to settle down on, it finds itself a crab. Typically, this will be a green crab, species Carcinus maenas. The female barnacle (more on the males later) crawls along the surface of the crab’s shell until she comes to a joint – a chink in the armour – where she turns into a sort of hypodermic needle, injecting herself into the crab and leaving her limbs and shell behind. Now nothing more than a tiny slug-like mass, she makes her way to the crab’s abdomen and proceeds to grow rootlike tendrils throughout her host’s body, drawing nutrients directly from the bloodstream.

If that wasn’t disturbing enough, consider Sacculina’s mode of reproduction. In addition to its internal root system, the parasite forms an external sac (hence the nickname ‘crab bag’) where the female crab normally keeps her fertilized eggs. This is where the male barnacle comes into play. Upon finding a crab already infected by a female, the male will do the same needle trick, injecting himself into the external sac and living for the rest of his life as a parasite inside the female’s body. Fertilization takes place and the sac is soon full of microscopic Sacculina larvae.

In case you needed a closer look.

Since the barnacle infection has rendered the host sterile, and because crabs aren’t very bright, the crab will now care for this sac of larvae as if they were her own young. But what if the infected crab was male, you ask? No problem. The parasite is able to interfere with his hormones to such an extent that, in addition to changing his body shape to that of a female, he now actually behaves like, and even carries out the mating gestures of, a female crab. Horrified yet?

Now, this may not seem so bad from the point of view of the crab; I mean, it doesn’t know it’s carrying around evil changeling spawn, right? But it’s a bit worse than that. Wanting to keep all the available energy for its own use, the parasite prevents the crab from moulting its shell or re-growing lost claws, as crabs normally do. This leads to a variety of secondary infections which, coupled with malnutrition, leads to the premature death of the crab. But nature isn’t without a sense of fair play… research has now found that Sacculina sometimes succumbs to viruses and yeast naturally present in the crab’s body, via infection of its rootlets. Take that, bloodsucking barnacle!

Says Who?

  • Powell & Rowley (2008) Diseases of Aquatic Organisms 80: 75-79.
  • Zimmer (2000) “Do parasites rule the world?” Discover Magazine (August issue).
  • Russell et al. (2000) Journal of the Marine Biological Association of the U.K. 80: 373-374.
  • Mouritsen & Jensen (2006) Marine Biology Research 2: 270-275.
  • Goddard et al. (2005) Biological Invasions 7: 895-912.
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The Curious Case of Turritopsis nutricula

Turritopsis nutricula

Common Name: The Immortal Jellyfish

A.K.A.: Turritopsis nutricula

Found: Tropical and temperate oceans around the world

It Does What?!

Ever been under a lot of stress and found yourself longing for the simplicity of childhood? What if, by force of will, you could actually turn back into your childhood self? And once you’d re-grown up, you could do it again. And again, and again… Welcome to the unusual lifestyle of Turritopsis nutricula, the so-called immortal jellyfish.

Jellyfish, also known as medusae (singular: medusa), are the mature life stage of Phylum Cnidaria, Subphylum Medusozoa. They start off as a bottom-dwelling structure that looks a lot like a series of plants connected by stolons (like strawberry plants… translucent, underwater strawberry plants). These “pseudo-plants” are called polyps, and when they mature, they bud and release many tiny medusae into the ocean, like a plant releasing pollen.

The polyp stage of Turritopsis nutricula

In most species, these medusae go off and live the jellyfish version of the good life- swimming, eating plankton, releasing sperm or eggs to be fertilized and form polyps for the next generation, and finally dying at the ripe old age of anywhere from a few hours to six months, depending on the species. Not so for the Immortal Jellyfish.

Reaching a size of only 4.5mm across, when Turritopsis nutricula becomes stressed, whether due to aging or a change in its environment, it can begin a process called transdifferentiation. First, its tentacles (80 to 90 of them in adults!) shorten and are re-absorbed into the body. The medusa becomes unable to swim and settles onto the bottom. It there transforms into a blob-like mass of cells and, within two or three days, forms a new polyp. In about a month, new jellyfish are ready to be released.

In theory, T. nutricula can pull this trick any number of times, which would effectively make it immortal. However, as scientists point out, these little guys frequently die from disease or predation before they can regenerate (Whovians, insert your own Doctor Who joke here), keeping the population under control. Not entirely under control, though, apparently- one researcher describes the spread of T. nutricula through the world’s oceans as a large-scale, “silent invasion.”  Beware the Immortal Jellyfish.

Says Who?

  • Miglietta & Lessios (2009) Biological Invasions 11: 825-834
  • Piraino et al. (2004) Canadian Journal of Zoology 82: 1748-1754

[Thanks to The Marine Biology Image Database for the use of these images: Migotto AE, Vellutini BC (eds). 2011. Cifonauta: marine biology image database. Available at http://cifonauta.cebimar.usp.br/ ]