Category Archives: Crustaceans

Arthropods vs. Cane Toads

Cane toads are toxic because their bodies are loaded with cardiac glycosides, deadly toxins that can stop a predator’s heart. Because the toads are non-native in Australia, the native Australian carnivores aren’t adapted to dealing with them. For some, this is very bad news: freshwater crocodiles, monitor lizards, and pythons have all experienced population declines since the introduction of cane toads in 1985 (Smith and Phillips 2006).

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A cane toad. Photo by Sam Fraser-Smith, licensed under CC BY 4.0.

Not all is lost, however. It turns out that cardiac glycosides are only toxic to a very narrow group of animals: vertebrates. Predatory insects, arachnids, and other invertebrates have no trouble at all with the poison. Furthermore, a study published earlier this year (Cabrera-Guzmán et al. 2015) revealed that many are more than capable of tackling amphibian prey.

Cane toads start their lives as tadpoles, small and innocent, but plenty toxic enough to kill a hungry frog or fish. In Australia, some of their top predators are giant water bugs and water scorpions. Both are insects (not scorpions) that use tube-like mouthparts to inject acid and digestive enzymes into their prey, dissolving them from the inside out. When the tadpole’s innards are sufficiently liquefied, the insects slurp them up like an amphibian milkshake.

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A water scorpion lying in wait for prey. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A young dragonfly's mouthparts. Photo by Siga, licensed under CC BY-SA 3.0.

A young dragonfly’s mouthparts. Photo by Siga, licensed under CC BY-SA 3.0.

Dragonfly larvae are also aquatic and predatory, but instead of using acid, they have extendable mouthparts. These are built like the robotic arm on an automatic garbage truck, but less cumbersome and more of a surgical, spring-loaded instrument of death. Most dragonfly larvae eat other insects, like mosquito larvae, but the largest species can easily overpower a small fish or tadpole.

Diving beetles join in the fun. Their mouthparts are less exciting, more like a typical beetle’s with sharp, biting mandibles. What makes them special is speed: their bodies are constructed like those of sea turtles. Like sea turtles, diving beetles are hard-shelled, streamlined, and aquadynamic. Unlike sea turtles, diving beetles use this form to swim after tadpoles that aren’t quite fast enough to escape.

A diving beetle, waiting for tadpoles to swim by. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A diving beetle, waiting for tadpoles to swim by. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A diving beetle larva with tadpole prey. Photo by Gilles San Martin, licensed under CC BY-SA 2.0.

A diving beetle larva with tadpole prey. Photo by Gilles San Martin, licensed under CC BY-SA 2.0.

Diving beetle larvae are just as fierce, and they too have been observed feeding on cane toad tadpoles. Unlike their parents, larvae are long-bodied, with curved, needle-like jaws which they use to inject digestive enzymes into their prey (like the water bugs).

Any cane toad tadpoles that survive this massacre can metamorphose into toadlets, but until they reach their adult size (4-6 inches) they are still at the mercy of their invertebrate predators.

Experiments and observations in the field (Cabrera-Guzmán et al. 2015) have revealed that crayfish are efficient predators of eggs, tadpoles, toadlets, and even adult toads. Australia is home to 151 species of crayfish, including several of the largest species on earth. The spiny crayfish (Euastacus) in particular, some of which can grow to more than a foot in length, prey not only on toadlets but also on full-sized, adult cane toads.

A Lamington blue spiny crayfish (Euastacus sulcatus). Photo by Tatters, licensed under CC BY-SA 3.0.

A Lamington blue spiny crayfish (Euastacus sulcatus). Photo by Tatters, licensed under CC BY-SA 3.0.

There are, believe it or not, spiders that specialize in running out over the surface of the water to snatch aquatic insects, tadpoles, and small fish. They are the fishing spiders (large ones are sometimes called dock spiders). Experiments have shown that when fishing spiders inhabit a pond, up to 1 in every 4 tadpoles ultimately becomes spider food (Cabrera-Guzmán et al. 2015).

A fishing spider, ready for a meal. Photo by Patrick Coin, licensed under CC BY-NC-SA 2.0.

A fishing spider, ready for a meal. Photo by Patrick Coin, licensed under CC BY-NC-SA 2.0.

Finally, ants. In the cane toad’s native range of tropical Latin America, meat ants are a major predator. When a toad is attacked, it often stays still, relying on poison for protection. Ants take advantage of this strategy, swarming over the toad’s body and stinging it to death with poisons of their own. Meat ants (Iridomyrmex) and their relatives also live in Australia, and they have been seen dragging the dismembered remains of cane toads back to their nests.

Meat ants taking down a cicada nymph. Photo by jjron, licensed under GFDL 1.2.

Meat ants taking down a cicada nymph. Photo by jjron, licensed under GFDL 1.2.

I’m sorry to say giant centipedes did not make the list of cane toad predators in Australia, but I should mention that the Caribbean giant centipede (Scolopendra alternans) has been observed to prey on native cane toads (Carpenter and Gillingham 1984).

Whether bird-eating spiders, bat-snatching centipedes, or tadpole-chasing water bugs, invertebrates that prey on vertebrates are always fascinating. It’s more common than you might think! I’ll conclude by mentioning Epomis, an unusual genus of ground beetles. Both the beetle larvae and adults are specialist amphibian-eaters, and tackle frogs and toads many times their own size.

Epomis beetles attacking various European amphibians. Photos from Wizen and Gasith (2011), licensed under CC BY 3.0.

Epomis beetles attacking various European amphibians. Photos from Wizen and Gasith (2011), licensed under CC BY 3.0.

I won’t say any more, since Epomis expert Gil Wizen has already written a fantastic blog post about these beetles, complete with videos of predation in action! I encourage you to check it out here.

Cited:

Cabrera-Guzman E., M.R. Crossland, and R. Shine. 2015. Invasive cane toads as prey for native arthropod predators in tropical Australia. Herpetological Monographs 29(1): 28-39.

Carpenter C.C. and J.C. Gillingham. 1984. Giant centipede (Scolopendra alternans) attacks marine toad (Bufo marinus). Caribbean Journal of Science 20: 71-72.

Smith J.G. and B.L. Phillips. 2006. Toxic tucker: the potential impact of cane toads on Australian reptiles. Pacific Conservation Biology 12(1): 40-49.

Wizen G. and A. Gasith. 2011. Predation of amphibians by carabid beetles of the genus Epomis found in the central coastal plain of Israel. ZooKeys 100: 181-191.

Shrimp-like Amphipods found in Sea Anemones

by Joseph DeSisto

Amphipods are crustaceans, similar to tiny shrimp. There are around 10,000 known species, with more being discovered each year. Most amphipods are marine and live as scavengers or predators, swimming or scuttling after tiny particles of food or plankton. A few are predatory, and use mantis-like front legs to snap up smaller creatures.

Stenothoe marina, related to the newly described amphipods. Photo by Hans Hillewaert, licensed under CC BY-SA 4.0.

Stenothoe marina, related to the newly described amphipods. Photo by Hans Hillewaert, licensed under CC BY-SA 4.0.

Last week’s new species are even more bizarre: they are “associates” living on the bodies of larger animals, ranging from sea anemones to mussels to hermit crabs (Krapp-Schickel and Vader 2015). So what exactly are they doing there?

Anemone-dwelling amphipods spend their time clambering over the tentacles of their host. Sea anemone tentacles are covered in microscopic stingers, to which the amphipods (like clown fish) are immune. Being surrounded by venomous tentacles might protect the amphipods from larger predators.

In turn, amphipods probably scavenge bits of detritus, such as uneaten prey, off the body of the anemone. One amphipod, however, does things a little differently. Instead of scavenging, it lives as a parasite, feeding on the flesh of its sea anemone host (Moore et al. 1994). Regardless, all of these amphipods have grasping, hook-like front legs called gnathopods (silent G), which they use to climb over and within the bodies of other animals.

Sea anemones. Photo by Francois Guillon, licensed under CC BY-SA 4.0.

Sea anemones. Photo by Francois Guillon, licensed under CC BY-SA 4.0.

Mussel-associated amphipods are more peaceful, but not entirely welcome, guests. Mussels are filter-feeders that extract plankton from the water, so instead of eating the mussel, amphipods steal some of the daily plankton catch (Tandberg et al. 2010). They are kleptoparasites, animals that steal their food.

Mussel-dwellers belong to the genus Metopa, and have surprisingly sophisticated lives (Tandberg et al. 2010). Each mussel is home to a single mating pair of adult amphipods, who defend their home against intruders. Most species spend their entire adult lives within the shell of a single mussel. In this time they work hard to raise multiple generations, which grow together until they are ready to head out to sea and find molluscan homes of their own.

A common hermit crab, host to a unique amphipod. Photo © Biopix: N Sloth, licensed under CC BY-NC 3.0.

A common hermit crab, host to a unique amphipod. Photo © Biopix: N Sloth, licensed under CC BY-NC 3.0.

Still other amphipods are described as hermit crab associates, some living on the crab’s acquired snail shell (Krapp-Schickel and Vader 2015). At least one species eats invertebrates that land and begin to grow on the shell. Others, however, live on the bodies of the crabs themselves.

This seems like a risky move. Hermit crabs are rigorous self-cleaners, constantly scrubbing the insides of their shells with specialized, brush-like hind legs. Perhaps the amphipods, by scavenging bits of uneaten food from the crab’s body, are helpful maids to their type-A hosts. If this is the case, hermit crabs may spare their amphipod companions on purpose. We still don’t know if the crab-dwelling amphipods are helpful cleaners or true parasites — if the latter is true, they must be well-adapted to avoid detection by their hosts.

Cited:

Krapp-Schickel T. and W.J.M. Vader. 2015. Stenothoids living with or on other animals (Crustacea, Amphipoda). Zoosystematics and Evolution 91(2): 215-246.

Moore P.G., P.S. Rainbow, and W. Vader. 1994. On the feeding and comparative biology of iron in coelenterate-associated gammaridean Amphipoda (Crustacea) from N. Norway. Journal of Experimental Marine Biology and Ecology 178: 205-231.

Tandberg A.H.S., C. Schandler, and F. Pleijel. 2010. First record of the association between the amphipod Metopa alderi and the bivalve Musculus. Marine Biodiversity Records 3, e. 5, 2 pp.

Saving the Easter Island Springtails

by Joseph DeSisto

By the time European settlers reached tiny Easter Island (Rapa Nui), far off the Pacific coast of Chile, it was already in ecological turmoil. The island had first been colonized by Polynesians as late as 1200 B.C.E. — their descendents comprise the Rapa Nui people, now the island’s indigenous population. They had at least 500 years before European colonization, and in that time the Rapa Nui people did great things — they constructed the world-renowned moai statues, for example:

Fifteen maoi -- on average, each of these is 13 feet tall and weighs 14 tons, but many are much larger. Photo by Ian Sewell, licensed under CC BY-SA 3.0.

Fifteen maoi — on average, each of these is 13 feet tall and weighs 14 tons, but many are much larger. Photo by Ian Sewell, licensed under CC BY-SA 3.0.

Despite the grandeur of the sometimes 30-foot-high moai, Easter Island already had its own wonders — the island was dominated by a species of palm tree, with trunks easily large enough to make a sea-faring canoe. That palm tree (Paschalococos disperta) existed only on Easter Island. I wish the picture below showed one of these trees, but that would be impossible — the Easter Island palm has been extinct for centuries. When European settlers arrived in 1722, the island was already almost completely deforested, with just a few pockets of forest left. Over the next few centuries, intensive sheep-grazing sealed the palm’s fate.

The Chilean wine palm (Jubaea chilensis) is the Easter Island palm's closest living relative. Photo by Scott Zona, licensed under CC BY 2.0.

The Chilean wine palm (Jubaea chilensis) is the extinct Easter Island palm’s closest living relative. Photo by Scott Zona, licensed under CC BY 2.0.

Today, the only evidence that palms ever existed on Easter Island come from petrified pollen grains and nut fragments (Flenley et al. 2006). The microscopic pollen grains are virtually indestructible and, in a cruel irony, have long outlasted the shepherds and, indeed, many of the moai themselves.

After such an environmental tragedy, it would be surprising to find any new species on Easter Island. And yet, even though every native vertebrate and many native plants have been driven to extinction, invertebrates that live exclusively on Easter Island continue to be discovered.

Just last week, biologists Taiti and Wynne (2015) published a survey of the woodlice (i.e., roly-polies) of the island, documenting two new species, one of which is only known from Easter Island. And that’s not all — a few months ago, five new springtails were introduced to science, unique to Easter Island (Bernard et al. 2015). Springtails are tiny, near-microscopic insect relatives that move by leaping extraordinary distances — if woodlice are the bumper-cars, then springtails are the bunnies of the micro-scape.

In profile: two new woodlouse species from Easter Island. Photo from Taiti and Wynne (2015), licensed under CC BY 3.0.

Two new cave-dwelling woodlouse species from Easter Island: Styloniscus manuvaka (left) and Hawaiioscia rapui (right). Photo from Taiti and Wynne (2015), licensed under CC BY 3.0.

So where are all these new species coming from? It turns out that even in such a desolate place as Easter Island, where almost all native wildlife and flora are gone, caves continue to provide a haven for undiscovered species (Wynne et al. 2014). All eight of these new species were found deep in caves, where humans have had less impact.

This is good news for those woodlice and springtails — now that we know they exist, perhaps we can keep them from following so many of their surface-dwelling brethren into extinction. After all, caves may be isolated, but they are not immune to our footprints. Keeping human traffic away from caves, and making sure the surrounding fern-moss habitat stays healthy, are both steps in the right direction (Wynne et al. 2014).

As a species, we have all but destroyed Easter Island’s fragile and unique ecosystems. Even so, in spite of our best efforts, a few native species, deep in the unexplored reaches of caves, persist. There is hope for them — and us — yet.

Cited:

Bernard E.C., F.N. Soto-Adames, and J.J. Wynne. 2015. Collembola of Rapa Nui (Easter Island) with descriptions of five endemic cave-restricted species. Zootaxa 3949(2): 239-267.

Flenley J.R., A.S.M. King, J. Jackson, C. Chew, J.T. Teller, and M.E. Prentice. 2006. The Late Quaternary vegetational and climatic history of Easter Island. Journal of Quaternary Science 6(2): 85-115.

Taiti S. and J. Wynne. 2015. The terrestrial Isopoda (Crustacea, Oniscidea) of Rapa Nui (Easter Island), with descriptions of two new species. ZooKeys 515: 27-49.

Wynne J.J., E.C. Bernard, F.G. Howarth, S. Sommer, F.N. Soto-Adames, S. Taiti, E.L. Mockford, M. Horrocks, L. Pakarati, and C. Pakarati-Hotus. 2014. Disturbance relicts in a rapidly changing world: The Rapa Nui (Easter Island) factor. BioScience 64: 711-718.

Accidental Conservation: Are Lobster Traps Helping Lobsters?

The American lobster is not a picky eater. A single study on a Nova Scotia population recorded such fare as seaweed, sponges, limpets, moon snails, periwinkles, whelks, flat skenia snails, mussels (their favorite), cockles, clams, chitons, bryozoans, barnacles, marine isopods, shrimp, crabs, other lobsters, sea cucumbers, sea stars, urchins, tunicates, fish, ragworms, scale worms, roundworms, ribbon worms, flatworms, happy worms, sad worms, wormy worms … you’ve probably skipped to the next paragraph by now, so I’ll stop. But this list is just an abbreviated version of the actual list, which is in the original paper (Elner and Campbell 1987) if you’re interested.

The point is, lobsters pretty much take what they get. That’s why lobstermen in the Gulf of Maine bait their traps with rotten herring — even though herring isn’t usually on the lobsters’ natural menu, the strong smell is enough to draw the curious crustaceans in.

An adult American lobster from Rhode Island. Photo by Rick Wahle, in public domain.

An adult American lobster (Homarus americanus) from Rhode Island. Photo by Rick Wahle, in public domain.

Once they get there, lobsters actually have a pretty good chance of getting away with a free meal. In 2002 a group of scientists planted cameras on lobster traps in New Hampshire to see how many lobsters were approaching traps on a nightly basis (Jury et al. 2002). Their results were astounding: of the lobsters that entered the traps to feed, only 6% stayed long enough to be caught. The rest escaped with bellies full of herring.

Roughly 70% of Atlantic herring caught in Maine ends up in a lobster trap. Photo by Chiswick Chap, licensed under CC BY-SA 3.0.

Roughly 70% of Atlantic herring caught in Maine ends up in a lobster trap. Photo by Chiswick Chap, licensed under CC BY-SA 3.0.

Unintentionally, lobstermen in the Gulf of Maine are providing lobsters with a portion of their diet. But just how important is bait herring to lobster populations in the wild? Grabowski and colleagues (2010) tried to answer this question by studying the diet of Maine lobsters. Using molecular markers in lobster stomachs, they compared the relative amounts of the most important natural prey (mussels, urchins, and crabs) with herring.

The results suggest that bait herring accounts for a whopping third to half of the total calorie intake of lobsters during the trapping season — once trapping ends for the year, only trace amounts of fish can be found in lobster stomachs. So herring is a major part of the lobster diet in heavily trapped areas of Maine, but is this good or bad for the lobsters?

These are juvenile American lobsters -- what they eat will affect how quickly they grow. Photo by Robert Huber, licensed under CC BY-SA 3.0.

These are juvenile American lobsters — what they eat will affect how quickly they grow. Photo by Robert Huber, licensed under CC BY-SA 3.0.

Grabowski and colleagues continued their research by recording the growth rates of wild lobsters both in heavily trapped and untrapped regions of Maine, as well as during and after the trapping season. They found that lobsters grew faster in heavily trapped areas than anywhere else, by about 15%. The same pattern was observed over several years, but the increased growth rate stopped soon after the trapping season ended, when bait herring was no longer on the menu.

Even though herring is rarely available to lobsters under natural conditions, bait herring is very nutritious and might help wild lobsters grow faster. If this is the case, the use of bait herring allows lobsters to reach maturity sooner, making Maine’s lobster fishery more sustainable. This is good news, both for lobsters and for the people and livelihoods that depend on them.

This article is a tribute to my time in Maine, where I grew up and where, this past weekend, I participated in the 13th annual BioBlitz at Acadia National Park. I also gave a public presentation on millipedes and centipedes at the Schoodic Education and Research Institute, which was a blast! You can watch the talk here.

Cited:

Elner R.W. and A. Campbell. 1987. Natural diets of lobster Homarus americanus from barren ground and macroalgal habitats off southwestern Nova Scotia, Canada. Marine Ecology Progress Series 37: 131-140.

Grabowski J.H., E.J. Clesceri, A.J. Baukus, J. Gaudette, M. Weber, and P.O. Yund. 2010. Use of herring bait to farm lobsters in the Gulf of Maine. PLOS One 5(4): e10188. doi: 10.1371/journal.pone.0010188

Jury S.H., H. Howell, D.F. O’Grady, and W.H. Watson III. 2002. Lobster trap video: in situ video surveillance of the behavior of Homarus americanus in and around lobster traps. Marine and Freshwater Research 52(8): 1125-1132.

Colorful Crabs: Meet the Grapsids

by Joseph DeSisto

A Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands. Photo by Anne Dirkse.

A Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands. Photo by Anne Dirkse, licensed under CC 4.0.

The creature above is a Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands, off the Pacific coast of South America. Found along the Pacific coast of the tropical Americas from Mexico to Peru, and on many offshore islands, these crabs get their name from their agility and speed on land (although why they should be called “Sally” is beyond me). On the Galapagos, where the Sally Lightfoot is especially common, their majestic red, yellow, and blue colors contrast beautifully with the black lava that makes up the shore.

They share the space with marine iguanas, and both species are abundant. While iguanas venture into the water to graze on seaweed, the crabs forage for food on land. Sally Lightfoots also eat seaweed but, being smaller and more nimble than their reptilian neighbors, can subsist on the smaller fragments that grow and are washed up between the tides.

Marine iguanas and Sally Lightfoot crabs share the rocky shores of the Galapagos Islands. Photo by D. Gordon E. Robertson.

Marine iguanas and Sally Lightfoot crabs share the rocky shores of the Galapagos Islands. Photo by D. Gordon E. Robertson, licensed under CC 3.0.

Sally Lightfoots belong to the family Grapsidae, which includes around 41 species of relatively large crabs, most of which are found along shorelines. Many are algae eaters, but like all crabs they are resourceful and will scavenge on small invertebrates and detritus.

Despite being called “shore crabs,” grapsids can live in a variety of habitats. These can include freshwater streams, mangrove swamps, and even drifting seaweed in the open ocean. Although many are accomplished land-lovers, they nonetheless have gills and so must remain moist in order to breath.

You might think it’s hard to beat the striking colors of the Sally Lightfoot, and you would probably right, but there are several other beautiful grapsids that deserve some limelight. So without further ado, here is the Sally Lightfoot’s Atlantic cousin, Grapsus albolineatus:

Grapsus albolineatus. Photo by S. Karthikeyan.

Grapsus albolineatus. Photo by S. Karthikeyan, licensed under CC 3.0.

And here’s the purple Leptograpsus variegatus from Australia, looking just a little sheepish:

Leptograpsus variegatus from Australia. Photo by Benjamint, licensed under CC 3.0.

Leptograpsus variegatus from Australia. Photo by Benjamint, licensed under CC 3.0.

Finally, my personal favorite, the striped shore crab Pachygraspus crassipes from the northern Pacific shores of North America and East Asia:

Pachygraspus crassipes. Photo by Matt Knoth, licensed under Creative Commons 2.0.

The striped shore crab, Pachygraspus crassipes. Photo by Matt Knoth, licensed under CC 2.0.

Tongue-Eating Parasites with Mayonnaise

by Joseph DeSisto

Tongue-eating parasites that are found in cans of tuna eat tuna, not human, tongues. But that’s a boring headline, so most news outlets left that part out when a woman in Britain found a “thing” in her can of tuna. The victim was one Zoe Butler, who opened her can of Princes tuna chunks this week to find an eyed, globular, undeniably cute invertebrate staring back at her.

Since the specimen was sent back with the tuna can to Princes, Stuart Hine of the Natural History Museum in London had to make do with a photograph in making his identification. He postulated that it might be a parasite related to Cymothoa exigua. Unfortunately, he also mentioned the common name, the tongue-eating louse, to reporters, who got right to work making sure the public knew that we were about to take part in a real-life version of The Bay.

What these reporters didn’t appreciate, sadly, is that the actual life history of Cymothoa is far more interesting and twisted than any sensationalist headline. These creatures belong to the crustacean order Isopoda, and are distantly related to woodlice. Unlike woodlice, however, Cymothoa are roly-poly fish nightmares.

Cymothoa exigua, a tongue-eating isopod. Photo by Marco Vinci.

Cymothoa exigua, a tongue-eating isopod. Photo by Marco Vinci.

As free-living larvae, Cymothoa are all males, and spend their time swimming about in search of a fish host. When several individuals “colonize” a fish, they begin feeding on its gills. If C. exigua is the louse, the host will be red snapper (not tuna). Once a fish has been parasitized, some males will change into females, and mating takes place on the gills or in the fish’s mouth.

The females are the tongue-eaters. Either before or after mating, depending on the species, a female invades the fish’s mouth and begins to suck blood. Extracting blood from the tongue eventually causes the tongue to wither away, after which the female persists on bits of mucus and blood remaining in the fish’s mouth. In C. exigua, this is when mating takes place: a few males will migrate from the host’s gills and mate with the female inside the fish’s mouth.

During all this time, the fish is still able to function, because the female Cymothoa functionally replaces the tongue. So with a new segmented, chitinous, leggy tongue, the fish can still eat and reproduce normally. Eventually, the female’s young emerge as free-living males, and disperse to find a new fish.

So, are tongue-eating parasites dangerous to humans? An adult female can bite in self-defense, and revealing a giant isopod while cleaning a snapper might be emotionally scarring. But rest assured, our tongues are safe. Enjoy your tuna.

For more information:

Driscoll, Brogan. “Mystery ‘Crab’ Found in Tuna Could Actually Be A Tongue-Eating Parasite, Claims Expert.” Huffington Post. 2 Feb 2015. Web. 6 Feb. 2015.

Creighton, Jolene. “Meet The Sex-Changing, Tongue-Eating Parasite.” From Quarks to Quasars. 3 Apr 2014. Web. 6 Feb 2015. <http://www.fromquarkstoquasars.com/the-most-horrifying-parasite-cymothoa-exigua/&gt;.