Fun biology facts: the world’s longest animal

November 28, 2012 • 12:37 pm

I bet you thought it was the blue whale (Balaenoptera musculus), didn’t you?—a beast that can be up to 30 meters (98 feet) long.  Well, there’s something that’s even longer, though way thinner: the bootlace worm Lineus longissimus.  According to a book I read on my trip, The Animal Kingdom: A Very Short Introduction, by Peter Holland, the worm can “certainly reach 30 meters, but claims in excess of 50 meters have been made.” I found that hard to believe, but checking Wikipedia (link above) I see that it can grow up to 55 meters (180 feet!).  Other sites substantiate that. The thing is, the worm is skinny (there’s a slight discrepancy here, since Holland says “the body of the worm is never more than a few millimeters wide” while Wikipedia says that the beast can be 5-10 mm wide). It’s in the phylum Nemertea, or ribbon worms.

At any rate, here’s some details and two photos:

Most likely present all around Britain and Ireland, except perhaps eastern Scotland and England.

Lineus longissimus is found on the lower shore coiled in writhing knots beneath boulders and on muddy sand. This species can often be found in rockpools entangled amongst Laminaria holdfasts or in rock fissures. In deeper sub-littoral areas, it occurs on muddy, sandy, stony or shelly substrata.

Lineus longissimus is an unsegmented, elongated ribbon worm. Young specimens range from dark olive brown to chocolate brown whereas adults are blackish brown to black. Epidermal cilia give the body a purplish irridescence. This species is the longest nemertean known. It is usually 5-15 m in length but can be over 30 m, usually 5 mm in width. The body is often streaked with pale longitudinal lines, especially on the anterior dorsal surface. The rectangular head has deep slits and ends in a pale colour tip. A row of up to 20 deep set reddish-brown or black eyes may be present either side of the snout. Pink or red cerebral ganglia may be seen through the epidermis.

© Copyright Malcolm Storey 2011-2112

From, oddly enough, Hawaii Dematology:

The species’ distribution from the Marine Life Information Network:

Wikipedia adds this:

The body is brown with lighter (longitudinal) stripes. Its mucus contains a relatively strong neurotoxin which it uses as a defence against predators.

When handled it produces large amounts of thick mucus with a faint pungent smell. A specimen washed ashore in the aftermath of a severe storm by St Andrews, Scotland, in 1864, had a length of more than 55 metres (180 ft),[2] longer than the longest known Lion’s mane jellyfish, the animal which is often considered to be the longest in the world. However records of extreme length should be taken with caution, because the bodies of nemerteans are flexible and can easily stretch to much more than their usual length.

Like other nemerteans, Lineus longissimus feeds using its eversible proboscis. As it is in the class Anopla, their proboscis is not armed with a barbed stylet. Instead they have a cluster of sticky filaments at the end of their proboscis that they use to immobilize prey.

Professor Ceiling Cat’s Big Question: Why is the damn thing so long? I’m a biologist but I have no idea why an animal that lives under rocks should be over 100 feet long.  That is, what’s the adaptive advantage of such a length? I suppose Larry Moran would say that it might be due to genetic drift (I don’t believe that, though), or it could be a byproduct of some other adaptation (I don’t believe that, either). Perhaps some worm-knowing readers could offer suggestions.

Although a book called The Animal Kingdom may seem dry, this one is short (120 small pages), up to date (how many animal phyla do you think there are now?), and packed with cool information.  I’ll highlight a few interesting animals from it in the next week or so.

And let me put in a good word for the Oxford University Press’s “Very Short Introduction” (VSI) series: there are about 300 now, each covering one field of inquiry; each short but well written and composed by an expert in the field. It’s the best way I know to get up to speed in areas like Quantum Mechanics, Animal Rights, Socrates, Developmental Biology, and so on.  I haven’t yet read the VSI Atheism book, by Julian Baggini, and, sadly, the VSI on Science and Religion, by Thomas Dixon, isn’t very good: it’s way too accommodationist.  But every other one I’ve read has been good. And they’re only about ten dollars each. Peruse the series and see if your interest isn’t piqued.

45 thoughts on “Fun biology facts: the world’s longest animal

  1. it could be a byproduct of some other adaptation

    The longer the gonads, the more eggs they produce?
    You’d expect sexual size dimorphism in that case though.

    1. Lineus are viviparous. They can reproduce asexually though, by breaking chunks of themselves, and are even able to regenerate a head on those chunks.

      I’m more inclined to think they grow that big as a response to plenty of food. They can survive starvation for a year or more.

  2. HERE’S the OUP Very Short Introduction catalogue at the UK site rather than the US site, but even some 10 year old titles are still being sold at full retail

    However almost all titles are available via the various Amazon sites [at around a 25% saving in the case of the UK]

  3. I’m not a worm expert by any stretch (so to speak), but I speculate that the point of growing so long is not length per se but surface area. If I understand correctly, the thing basically never stretches out to its full length, but remains coiled up in a mass. So it seems plausible to suppose that it gains some advantage from having a high surface-to-mass ratio, and the way it achieves that is by being long and skinny.

    What advantage might that be? I have no idea. Perhaps it breathes or absorbs water or nutrients through its skin? Just guessing.

    1. OIC, so it’s a way of growing bigger while maintaining surface area instead of have to do all that tedious mucking about with lungs?

    1. I was about to ask the same question. They must be very vulnerable to such injuries.

      Could the extreme length be some kind of adaptation to survive predation? The predator gets some of the worm, but there’s enough left for it to survive.

      1. That’s actually what I had in mind.

        If being cut in half is fatal to these worms, then it’s a huge problem. But if it means that there are now two worms where there was only one, it’s a bonus.


        1. Given the way it is typically coiled, I would think a simple bisection would be rare. I would think it would be split into many pieces by any physical attack.

          I like the surface area speculation.

  4. Jerry – Off the topic. It was just reported that a new species of lion has been discovered in Ethiopia according to genetic studies. This lion is reported to have a darker mane and smaller body than other lions. What do you think?

    I have heard that studies have been done that indicate darker and larger manes are more attractive to female lions. Also reduced size of animals usually indicates fewer resources (prey) over time. My guess is that these Ethiopian lions can still mate with other lions. Why is it claimed these lions are a new species rather than just a subspecies? Any thoughts? Thanks

    1. I think that typically, a population will be classified as a separate species if it’s genetically isolated from the base species and it shows significant enough physical distinction, but the cutoff is probably arbitrary. Africa’s had a few large mammals that have been previously listed as a single species but recently split into multiple groups- the square-lipped rhino (divided into a Northern and Southern species) and elephant (divided into the savannah elephant and Forest elephant) both come to mind.

      And there are plenty of species that are capable of interbreeding and producing fertile offspring- bonobos and chimpanzees have done so in captivity while brown bears and polar bears apparently do so in the wild.

  5. Where is the toxic mucus secreted from? If the whole outside of the body produces it, maybe the worm uses its greater surface area to produce the amount of mucus necessary to have an effect. (Disclaimer: not at all a worm expert)

  6. As a senior software engineer*, if I had to guess for the reason of the length it would be for traction in a tidal, wave swept environment. A longer body (with large surface area as per Gregory Kusnick #4 comment) would have greater ability to not get swept away in rough coastal waves. Imagine a short worm poking part of its body out on a beach and a large wave sweeping in: it would have little chance to “hang on” and it would get washed away.

    Note the distribution of the worm in the map shows the most wave-action effected parts of the coastlines.

    * Just to note my qualifications which can be used to gauge my biology speculations 🙂

  7. I want to plug H.G. Wells’ A Brief History of the World. Yes, it’s western-centric and a little dated; but it’s a brilliant work of concision. His Outline of History is also excellent; but the Brief is really amazingly concise.

  8. Could be that lives on a very poor diet and has a VERY long gut to try and extract every last ounce of nutrient out its food, much the way our coiled intestines vastly increase the nutrient absorption compared to it were a straight tube through the body.

  9. A bit off-topic, but I felt like it was important enough to report to Jerry immediately…

    Richard Dawkins tweeted this heresy about four hours ago:

    Jerry Coyne’s blog is truly delightful…

    Oh, the horror. LOL 😉

  10. I really like the VSI series. I have a dozen and have read half already. The atheism one was well written but you were correct about the science and religion one, too accomm. Worm looks like good eating though.

    1. My younger brother still hasn’t forgiven me because I “made him” kiss a worm when he was 5 (and I was 7).

      Now, I did not technically “make him” kiss the worm. I presented it to him and said “kiss it”, which he did voluntarily. No arm twisting or threats of violence of any kind were used.

      Yet, I still “made him” kiss the worm. Somehow, this led to a world of sorrows.

      No. No worms shall be kissed (or eaten) by me or my kinfolk. No good can come of it.

  11. The VSI on Darwin, by Jonathan Howard, came out in 1982, and was repurposed as a VSI in 2001. I read it in 1984, and my recollection is that it was pretty good. Looking at my copy now, I did note that Howard wrote that Jimmy Carter was a biblical literalist, which isn’t true.

      1. I remember that, it was the episode I was looking for when I went on wikipedia and found out they corrected their mistake. It was played very quietly, still strange how Alan said Blue Whale like the question has never been asked before. In the comments of your link Rolfe mentions this, it has happened more than once! I feel dirty for criticising QI.

          1. My only source is the Oxford English Dictionary, available online as a member of City of London Libraries. This is a bit long but I think scuppers their argument: English ‘cat’ almost certainly doesn’t come via Latin.

            [The ME. and mod. cat corresponds at once to OE. cat and ONF. cat. The name is common European of unknown origin: found in Lat. and Gr. in 1–4th c., and in the modern langs. generally, as far back as their records go. Byzantine Gr. had κάττα (in Cæsarius c 350) and later κάττος, as familiar terms = αἴλουρος; mod.Gr. has γάτα from Ital. Latin had catta in Martial a 100, and in the Old Latin Bible version (‘Itala’), where it renders αἴλουρος. Palladius, ? c 350, has catus, elsewhere scanned cātus (Lewis and Short), and prob. in both cases properly cattus. From cattus, catta, came all the Romanic forms, It. gatto, Sp., Pg. gato, Cat. gat, Pr. cat, ONF. cat, F. chat, with corresponding feminines gatta, gata, cata, cate, chate, chatte. The Teutonic forms recorded are OE. cat, catt, ON. kött-r (:—kattuz) masc., genit. kattar (Sw. katt, Da. kat); also OE. catte ? fem., WGer. *katta (MLG. katte, MDu. katte, kat, Du. kat, also Sw. katta), OHG. chazzâ (MHG., mod.G. katze) fem.; OHG. had also chataro, MHG. katero, kater, mod.G. and Du. kater, he-cat. The OTeut. types of these would be *kattuz masc., *kattôn- fem., *kat(a)zon- masc.; but as no form of the word is preserved in Gothic, it is not certain that it goes back to the OTeut. period. It was at least WGer. c 400–450. It is also in Celtic: OIr. cat masc., Gael. cat com., Welsh and Cornish cath f., Breton kaz, Vannes kac’h m. Also in Slavonic, with type kot-: OSlav. kot’ka f., Bulg. kotka, Slovenish kot m., Russ. kot m., kotchka, koshka f., Pol. kot (koczur m.), Boh. kot m., kotka f., Sorabian kotka; also Lith. kate; Finnish katti.
               (These forms indicate extensive communication of the word, but do not fix the original source. History points to Egypt as the earliest home of the domestic cat, and the name is generally sought in the same quarter; Martial’s attribute might incline us to a Slavonic or Teutonic origin:    c 75 Martial xiii. 69 Pannonicas nobis nunquam dedit Umbria cattas.    a 250 Baruch vi. 21 (‘Itala’) Noctuæ et hirundines et aves, similiter et cattæ [LXX. καὶ οἱ αἴλουροι].]

  12. Seeking clarification;

    When you ask “why so big” are you asking about the “normally 5-15 M” or the “can be >30 M”?

    Since it appears most of the population fall in the 5-15 M range, it is reasonable to ask why they grow this long. But since the 30+ M beasts are rare, it is quite reasonable to to suggest that the extreme lengths are a by-product of continuous growth (get me to 10 M ASAP!!), as observed in many marine Nemertea.

  13. I have just bought the VSI to American History, VSI to Religion in America and VSI to Christian Ethics for reading when I’m in the states next month. Most bookshops here have the VSI series in 3-for-2 offers. Excellent little things for getting good overviews.

  14. More curious to me rather than the length is the distribution – is it not found on coast of the Isle of Man? Or east Scotland, yet is further south on the North Sea coast? Not found in other parts of the coast of Europe? Does it have free swimming offspring? How does it reproduce? etc etc!

    1. That is an odd distribution which I was wondering about. The NE coast of Scotland is rather sandier than the average, but that begs the question of why it’s not reported on the Moray Firth coasts.
      If I remember, I’ll ask some of the people from the local Marine Lab the next time I see them at the SCUBA club.

  15. I’ve read several Vsi’s :

    Viruses, Statistics, Mathematics, Classics, Ethics and Globalization. The maths one is written by a winner of the Fields Medal- Timothy Gowers, and is very good. The Stats one is very good too.

  16. Now, I’m pretty sure that I’ve seen these unappealing slimy piles on various bits of sea shore. But I never knew that they were even slightly interesting organisms. I always just classed them as “poo avoid”.
    Next time we’re beach-walking, I’ll deflect the wife’s “ewwww!” reaction in this direction while I poke and prod.

    1. Re poking and prodding: remember those neurotoxins.

      Also, look before you poke: an iridescent worm under an intertidal rock could be a polychaete with razor-sharp chitinous jaws. (You won’t even feel the bite when it slashes your hand open, if it’s like one I met)

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