Although I have to admit I was cheering for the worm at the end of this video. Come on, little squidworm! Evade that vacuum tube! I have no idea why. I’m all for science.

As you can see, the key feature of the squidworm are its voluptuous tentacles. You can get a much better look at them here. According to my admittedly scanty sources, the squidworm lives in the deep (ca. 10,000 feet, or nearly two miles down) and feeds on marine snow, a mixture of fish poop and dead plankton. I’m glad I don’t have to eat marine snow. I have to imagine it has the taste and consistency of that gruel from The Matrix . . .

What is unclear is whether they use those tentacles to grab their food, although I would imagine that is the case because most tenatculated organisms do. (UPDATE: According to information here, eight of its tentacles are used for breathing (gas exchange of CO2 and O2 by increasing the surface area for it) and the two that are loosely coiled in this picture are indeed for feeding. I don’t count eight of the other tentacles in the picture, but if the scientists say so. . . )  In any case, recall that polychaetes as  a group are characterized by lateral body extensions called parapodia (what look like their feet) that have bristly extensions called chaete (“kee-tee”), hence the name polychaete for the group. Polychaetes come in a vareity of splendiferous forms, including the christmas tree worm, the Pompeii worm, the recently discovered Osedax whale-bone-boring worm, and the Methuselah-esque (life expectancy: something like 250 years) cold methane seep tube worm Lamellibrachia. Polychaetes, in turn, are annelid (segmented) worms, like our old friend the earthworm. You can see how everyone is related (sort of — science in progress) here.

The squidworm stands out among polychaetes in a few ways: it is free-swimming, while most are tunnelers of the sea floor. It also has six pairs of oppositely branched nuchal organs — cilia-lined structures typically found in pits and used for smelling or sensing things. I’m not sure where those are located in the pictures. And its got those tentacles, which are as long or longer than its body.

Finally, the squidworm was discovered in the Celebes Sea. Where is the Celebes Sea? you may be wondering. GOOD QUESTION. I did not know either, so I looked it up. It’s in southeast Asia, just to the south of the Philippines and sorta midway between Australia and Vietnam.

And now you know.

In this first video you can see our subject looking kind of cute and shy (awwww!). Pay attention to the dorsal (top) vessel and you’ll see the “human-like blood” being pumped through the worm’s closed circulatory system (just like us!). In Nereis, the dorsal vessel itself does most of the pumping. Also note double eye spots (this guy is literally a four-eyes) and the leg-like parapodia with their bristly setae.

But in this video you’ll find Nereis has a second, distinctly not cute side: vicious predator. Watch for it to evert its pharynx, and particularly watch for the TWO GIANT FANGS (technical term: jaws) on the end. You can also see the pumping blood at the beginning of this film. Unfortunately, this one is a bit dark.

Although you may be tempted to think these guys are closely related to millipedes and centipedes, they’re not. This is yet another case of  — you guessed it — convergent evolution.

. . . Is not the name of a new DARPA grant project. All over teh intert00bz this week was the story of a newly discovered group of annelid polychaete worms following the publication of a paper describing them in Science. Remember annelids? Segmented (often) worms? The ones with the “human-like” blood? Like tube worms and sludge worms and . . . oh yes, of course, leeches and earthworms. Let’s have a look, courtesy Ed Yong:

Ok, well that’s pretty cool, but not too much to see here. Built like a trireme, moves like a belly dancer, swims in the deep ocea. . . . holy ****! It’s got glowing green sacs of goo on its neck that it launches like floating chinese lanterns when poked!

Swima sp. Used with permission courtesy Karen Osborn

Wow! According to the scientists who discovered them, the worms are probably using these like submarine countermeasures — the old lure-the predator-towards-the light while you scuttle quietly away. There are four bomb docking points on either side of the neck (the authors call them “bomb bays” in the paper’s supporting material). The worms seem kinda stingy with them, though, and will only release a few at a time if poked. It probably takes them a while to grow back. The authors had the guts to name the genus Swima, and one species Swima bombviridis — the swimming green bomb.

The bomb throwers aren’t rare, either. They are large (a few centimeters long), common organisms that are fairly widely distributed, judging by their pads off both the coast of California and the Phillipines.

And there are many different sorts. Here’s a tree illustrating some relationships between the groups.

A proposed family tree for the genus Swima. Note the bodies are transparent except for the gut. Used with permission, courtesy Karen Osborn.

Inside each bomb are two large and two small compartments that are probably breached when the bomb is ejected to mix chemicals that react to light up the whole sac. At a historic site at Rocky Mountain National Park a few weeks ago I heard about a similar concept in fire extinguisher design from the 1920s. . . break glass to mix chemicals, which react to remove any oxygen, fire, and aerobic life from the room. I’ll stick with my red cylindrical pressurized mace, thank you very much.

Ah-hem. Polychaetes. Right. These worms are polychaetes, which means, roughly, many bristles. The bristles (called setae) are made of a very interesting polysaccharide called chitin, which is found, strangely enough, in hard invertebrate body parts and the cell walls of fungi. Setae extend from parapodia, or foot-like projections from each segment. The parapodia are rife with blood vessels that help the animal exchange oxygen for carbon dioxide.

On the left, a trochophore larva. "One day I will be a beeee-utiful chiton". Center, metamorphosis. At right, a juvenile.

And polychaetes have a very interesting ciliated larval form called a trochophore; that is, they have lots of little filaments that beat back and forth to move it around. Annelids aren’t the only group that has trochophores; mollusks and a few others do too. If you saw one floating in the ocean on its own, you might think it was a protist, or single-celled microbe (hmmm. . . . ). In order to get a big polychaete, the trochophore starts adding segments, and presto chango, you have annelid worm! Above is a picture of the general process for a chiton, a kind of mollusk.

The variety of known polychaetes, ca. 1800s. I love these 19th century biodiversity prints. Question: Why are they all by Germans? "Borstenwurmer des Meeres". A variety of marine worms. In: "Das Meer" by Matthias Jacob Schleiden, 1804-1881. P. 446. Library Call Number QH91.S23 1888. Image ID: libr0409, Treasures of the NOAA Library Collection

There are some 10,000 known polychaete species in a variety of hallucinatory flavors. Some are free-swimming, like Swima, while others live in tubes or burrows. Many are brightly colored, like christmas tree worms, fan worms, and peacock worms. You can get an idea of the cutting edge knowledge of polychaete diversity (ca. 19th century) from the print at right. Only the freshest and most up-to-the-minute science for you, dear readers.

Yet it is assuredly, despite its intriguing diversity, miserably outdated. We didn’t even know that this major, distinctive polychaete group existed until one swam in front of a submersible in 2001. What else don’t we know about?

For a nice slide show of various Swima species, check out this gallery by National Geographic.