Marine life facts that read like fiction, checked

These ten marine life facts come from the Fact Drop library, and each one sounds like something a pub quiz made up. I opened the page behind every one of them. Most hold up. A few lose a condition on the way to the headline, and I have marked where.

The sea animals here sit on the library's animals page and its ocean page. An earlier roundup read ten ocean facts against their pages, and none of those are repeated.

How long can a sea animal live

A clam that was 507 years old

The library's oldest known animal is an ocean quahog dredged off Iceland in 2006 and later nicknamed Ming. Its age was counted from growth lines in the shell, first as 405 years and then, after a second count in 2013, as 507 [1].

The headline skips how it died. The page says it plainly: "Ming died in 2006 when it was frozen by researchers who were unaware of its exceptional age" [1]. Counting the lines also meant cutting the shell open, since the page notes the clam must be killed to find its age.

A shark that may wait over a century to breed

Greenland sharks grow slowly. A shark tagged in 1936 and caught again in 1952 gave the figure on the page: "Its measurements suggest that Greenland sharks grow at a rate of 0.5-1 cm" per year [2]. The library's "about a centimetre" is the top of that range.

The breeding age is softer than it looks. Wikipedia says they mature at around 150 years of age [2]. A 2020 paper in PLOS ONE, which the article cites, says its length data "suggests that females reach sexual maturity no earlier than 134 years of age" [3]. That is a lower bound, and it covers females only.

A jellyfish that runs its life backwards

Turritopsis dohrnii can turn from an adult medusa back into a polyp colony when it is stressed, hurt, sick or old, by changing one cell type into another [4]. The page says that in theory "this process can go on indefinitely".

What the nickname "immortal jellyfish" leaves out is the next line: "In nature, most Turritopsis dohrnii are likely to succumb to predation or disease in the medusa stage without reverting to the polyp form" [4]. The trick exists. Most of them never get to use it.

What are the oddest bodies in the sea

A punch that lands twice

The mantis shrimp in one species, Odontodactylus scyllarus, swings its club at 23 metres a second from a standing start [5]. That is fast enough to pull bubbles of vapour out of the water, so "the prey is hit twice by a single strike; first by the claw and then by the collapsing cavitation bubbles" [5].

The flash of light in the library's version is on the page too. The collapsing bubbles "also produce light, which is termed sonoluminescence" [5]. "Boil" is the library's word, though. The page calls them cavitation bubbles and never says the water boils.

The biggest eye, with a maybe attached

The library says the giant squid has the largest eye of any animal. The page hedges: "It also has the largest eyes of any living creature except perhaps the colossal squid" [6]. Those eyes reach at least 27 cm across, with a 9 cm pupil [6].

The library adds that the eye is built to spot sperm whales. I could not find that on the page. It says large eyes "can better detect light", including light made by living things, which is scarce in deep water [6]. Sperm whales do appear there, as the squid's chief predator.

A head you can see through

The barreleye keeps its tube-shaped eyes inside a "large transparent dome of soft tissue", as its Wikipedia entry puts it. The eyes mostly point up, to catch the outlines of prey against the faint light above, and they can turn to face forward.

That entry also gives a reason for the dome that the library leaves out. It likely shields the eyes from the stinging cells of siphonophores, the drifting colonies the barreleye is believed to steal food from.

A colony that works as one

The Portuguese man o' war is a siphonophore, a colony of smaller units called zooids, according to its Wikipedia entry. Seven types of zooid have been described, each with its own job, and they "depend on each other for survival".

Where the library drifts is the phrase "separate creatures". The page says every zooid grows from one fertilised egg and is genetically identical. Together, it says, they "allow the colony to operate as a single individual".

A male that fuses with the female

In some deep-sea anglerfish the small male latches onto a much larger female with his mouth, and the pair can fuse. The page calls this sexual parasitism, and says "fusion between male and female when reproducing is possible due to the lack of immune system keys" that let antibodies mature [7].

The size gap is on the page as well. Males of one species measure 6.2 to 7.3 mm at maturity, against females of 50.5 mm [7]. The library's line about the male wasting away into a sperm-making appendage goes further than this page does, and I did not find it there.

What do sea animals do for people, and for a mate

Blood that checks vaccines

Horseshoe crab blood turns to gel when it meets bacterial toxins, which Fred Bang reported in 1956 [8]. The US Food and Drug Administration approved the LAL test in 1977 for drugs and devices that touch blood, replacing a slower test on rabbits [8].

The library ends with the crabs being bled and returned to the sea. The page is less tidy: "some crabs are then returned to the water, while others are sold to be eaten or used as bait" [8]. A 2009 Massachusetts study it cites found 22% mortality in females put straight back, and 30% in females kept overnight [8].

A sand circle that takes a week

The white-spotted pufferfish, about 10 cm long, builds a circle two metres across on the seabed off Amami Ōshima in Japan, as its Wikipedia entry records. Each one is formed in 7 to 9 days, and the male "works for more than a week straight", flapping his fins to raise the ridges.

The library says the circle exists only to persuade a female to stay. The page gives it a second job. The centre is where she may lay her eggs, he guards them until they hatch, and males never reuse a nest.

Questions

What is the oldest animal ever found?

The oldest single animal whose age could be counted precisely is Ming, an ocean quahog clam dredged off Iceland in 2006 [1]. Growth lines in its shell put it at 507 years old, a figure checked against other shells and carbon dating. Greenland sharks may rival it, with one estimated at 392 years give or take 120, but those ages carry much wider error [2].

Is the immortal jellyfish really immortal?

Only in theory. Turritopsis dohrnii can turn from an adult medusa back into a young polyp colony when it is stressed or old, and its page says the cycle could repeat with no end [4]. In the wild, though, most die from predators or disease as medusae before they ever revert. The trick resets age. It does nothing about being eaten.

Are horseshoe crabs killed for their blood?

Some are. Companies said before 2008 that mortality was below 3%, but a 2009 Massachusetts Division of Marine Fisheries study found 22% of bled females died even when returned to the water at once [8]. Some bled crabs are also sold as food or bait. A lab-made substitute, recombinant factor C, has been on sale since 2003 [8].

Which animal has the biggest eyes?

The giant squid or the colossal squid. The giant squid's eyes reach at least 27 cm across with a 9 cm pupil, and its page says only the colossal squid may beat it among living animals [6]. Of extinct animals, the ichthyosaurs are the only ones known to have had larger eyes.