Fun biology facts: the world’s longest animal

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.