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When it comes to mollusks, people talk a lot about the charismatic giant squids and giant clams (and for good reason!), yet, to my mind, these are not the strangest—or even the most elusive–giant mollusks. Scientists have long sought a very different creature—the giant shipworm (Kuphus polythalamia)—which they knew from its bizarre meter long tubal shell. Yet despite the fact that such shells were (relatively) plentiful—marine biologists never found a living specimen…until this spring, when internet clips revealed footage of people eating huge shipworms in the Philippines. Researchers were thus led to a remote lagoon in the archipelago where at last they discovered living giant shipworms flourishing in the foul muck. What they then discovered was the most shocking thing of all…
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But first let’s provide some context. Shipworms are bivalve mollusks (like clams, oysters, and mussels) which eat wood–a surprising amount of which finds its way into the oceans. Wood is extremely difficult to digest, since it contains lignins, cellulose, and such like tough organic polymers. Shipworms digest wood the same way beavers and elephants and termites do—with help from symbiotic bacteria. This made shipworms the bane of pre-industrial mariners (who counted on intact wooden hulls in order to remain alive).

But shipworms are small, and the giant shipworm is…giant. The fact that the giant shipworm is an insane 130 cm long cylindrical clam with a gun metal blue body and obscene flesh gills which lives in a huge calcium tusk the size (and shape) of a baseball bat is not at all the strangest aspect of the creature. What is most odd about this mollusk is how it eats: it doesn’t. The foul anaerobic slime at the bottom of that lagoon in the Philippines is rich in hydrogen sulfide from decaying organic matter.
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The giant shipworm doesn’t eat this decomposing matter (indeed, its mouth is all but vestigial). Instead it has bacteria in its gills which live upon hydrogen sulfide. The giant shipworm survives off of the byproducts of this bacterial respiration. It grows huge off of toxic gas. This strange metabolic cycle is of great interest to scientists for what it reveals bout symbiosis, adaptivity, and metabolism. Perhaps someday it will be useful as well. Maybe future generations of explorers will love giant shipworms for their ability to live on waste product gases just as much as vanished generations hated shipworms for eating ships.

Opah?

Opah?

In all of entertainment, no figure is more beloved than Opah!  Her networks make the most money.  Her endorsements confer instant fame and wealth.  Her personal life is the subject of profound fascination and scrutiny. She is what all Americans aspire to be…a veritable queen who transcends…

Opah!

Opah!

Wait…Opah?  That’s a big orange fish! Also known as moonfish, opahs consist of two species (Lampris guttatus and Lampris immaculates) which are alone in their own small family the Lampridae. Their closest relatives are the magnificent ribbonfishes like the crestfishes and oarfish! They are discoid fish with orange bodies (speckled with white) and with bright vermillion fins.  Opahs do not give away cars or support quack psychiatrists and physicians, but, they are much in the news right now anyway. To the immense surprise of ichthyologists and zoologists, a research team from the NOOA has discovered that Opahs are warm-blooded—in a way.  They are the only endothermic fish known to science.

Lampris guttatus (NOAA)

Lampris guttatus (NOAA)

Being warm-blooded allows animals in the deep ocean to think and move more swiftly than the more ascetic and staid dwellers of the deep (most creatures of the ocean bottom are usually slow and placid in order to conserve energy–like the tripod fish).  Ocean birds and marine mammals have long used this to their advantage.  They gulp air from the surface and then dive deep to catch slower moving fish, squid, and invertebrates from the cold depths.

A stamp from  French Southern and Antarctic Territories showing Lampris immaculatus

A stamp from French Southern and Antarctic Territories showing Lampris immaculatus

Other high-speed predatory fish (certain species of sharks and sportsfish) can warm key muscle groups using heat exchanging blood vessels in order to gain a burst of super speed, but these fish rapidly lose their heat—and the related speed advantages–as their blood circulates through their gills. This is one of the reasons sharks and marlins lunge and then return to slow measured swimming.

The opah appears to produce the majority of its heat by constantly flapping its pectoral fins.  The warmth thus generated is not lost through the opahs’ gills. Critically, these fish possess unique insulated networks of blood vessels between their hearts and gills.  The residual heat is removed from blood headed through the gills and then restored as it goes back through the heart. Their weird circular shape and comparatively large size are additional adaptations to help them conserve this warmth.

An opah near San Clemente Island (Jane J. Lee for National Geographic)

An opah near San Clemente Island (Jane J. Lee for National Geographic)

Marine biologists know surprisingly little about opahs (especially considering that the fish have long been known to fishermen and diners).  Opahs live in the mesopelagic depths 50 to 500 meters (175 to 1650 feet) beneath the surface but it now seems they might make deeper hunting forays into the true depths.  They are solitary hunters which live on shrimp, krill, and small fish. Opahs are approximately the size of vehicle tires.  The smaller species (Lampris immaculatus) is like a big car tire and reaches a maximum of 1.1 m (3.6 ft). The larger species, Lampris guttatus, can become as large as an industrial lorry tire and can attain a length of 2 m (6.6 ft).  the largest opahs weight up to 270 kg (600 lb).

Spotted Opah larva (Lampris guttatus)

Spotted Opah larva (Lampris guttatus)

Larval opahs resemble the larvae of oarfish (they are long and ribbonlike with strange protuberances.  The main predators of Opahs are the great sharks…and humankind.  Because of predation from this latter species which is endlessly hungry the survival of the opahs has grown less certain.  It is believed that they have a low population resilience, but this…like their numbers and their lifestyle is unknown to science.  We only just found they were warm-blooded earlier this month!

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