February 17, 2013 | 5
Consider this image:
Would you have guessed it is from a U.S. government publication? Here it is in its original context (don’t miss the caption!).
Here’s another, of a free-living marine nematode called Draconema (see photos of actual Draconema here):
Wait. This work of art, laid out as if it were a children’s storybook, was produced by a government? OUR government?! Yes. It’s from the 1914 Yearbook of the U.S. Department of Agriculture, which has probably never looked sexier. Its collection of public domain nematode pinups is perfect for your home, office, or next science-themed tattoo.
Just a few weeks ago Rob Dunn discussed a gem of a paper he had stumbled into in a library. I stumbled on to another such hidden gem when I was writing my last post on nematodes. It is “Nematodes and Their Relationships“, by Nathan Augustus Cobb, the same man who wrote the Dissolving Earth Nematode Thought Experiment (DENTE) I quoted in my last post. I dipped into “Nematodes and Their Relationships” to verify Cobb was the source of the quote. The images I discovered there made my jaw drop. I had to share them.
Despite their reputation as simple round white worms, and in spite of the impression my last post may have given, nematodes — especially free-living nematodes — are beautifully diverse. They also comprise the majority of the group.We tend to think of nematodes as plain because the parasitic variety, which have little need for bells and whistles, usually look that way. Though Cobb was what we would today call a plant pathologist, he made or found plenty of time to study the ornamented, free-living, non-plant-harrassing nematodes of the world. And he drew them. Gloriously.
Over the course of his 40-year career, Cobb would work in Australia, Hawaii, and finally Washington, D.C., studying and publishing on a bewildering variety of plant diseases, and even designing a cotton fiber grading system. He was a skilled microscopist who created new mounting methods and clever improvements to contemporary scopes. But his specialty was nematodes, and he is considered the Father of Nematology in the U.S. He identified over 1000 species.
To appreciate Cobb’s art in the 1914 USDA Yearbook, it will help to know a little bit more about nematode biology.
Inside each worm is a pharynx and simple gut, some nerves and muscles, some gonads, and a simple excretory system for ridding the animal of excess salt. Roundworms also possess a collagen cuticle (a molecule found in most animals’ bodies, including yours) encasing a one-celled epidermis. In the second photo on this page, you can see a nematode struggling to free itself from a fungal sticky trap actually pulling itself away from its own cuticle.
From the outside, a roundworm is just that — round and wormy. But, as we saw with Draconema above and with other examples below, there is tremendous variation on that theme among the free-living roundworms. Roundworm cuticles, for instance, may be decorated with rings, bristles, or ridges.
Here is one with “warts”:
Here is one with bristles that seems very un-nematode like in that it’s not transparent (click here for an actual photograph of this Desmoscolex):
And here is one armored in backward-pointing plates. This prevents the roundworm from slipping backward in the soil when it uses its stylet — a mouthpart described below and visible at the top of this drawing — to stab something.
Roundworms have a few anatomical quirks. Within a particular species and gender, each animal contains the same number of cells. For example, every male of the laboratory nematode Caenorhabditis elegans contains 1,031 cells, and the developmental path of each and every one of them has been mapped. This has a cute biological name — eutely — and is also a property of the little animals called rotifers discussed here a few posts back. Why that might be advantageous, or whether it is at all (perhaps it is simply a byproduct of roundworm development), remains a puzzle.
Here’s another quirk: although their bodies are bilaterally symmetrical, like that of a human, nematode heads are radially symmetrical, like a starfish. Roundworms may have either three or six jaws, often lined with teeth.
You know what this should bring to mind, of course. That’s right. Shai-hulud.
In the semi-official Dune Encyclopedia, sandworms are actually given the scientific — if idiosyncratically spelled — name “Geonemotodium arraknis”.
Here are drawings of the mouthparts of two real nematodes from the 1914 yearbook:
Here’s another belonging to a — I am not making this up — shark nematode missing one of its three jaws, as Cobb notes below.
Do you see the little organ on the right and left sides of the shark nematode’s head? They are called amphids, and they puzzled Cobb.
Today we know these cryptic, paired structures are chemical and heat sensors.
Sometimes, in place of the fearsome jaws we just saw, a nematode may have a piercing stylet, as we saw in the etching of Xiphinema at the top of this post. These are generally used for stabbing and sucking things — whether animal, protist, or plant — as we saw in video of the predaceous nematode last time.
But roundworms may also have other surprisingly delicate or fearsome appendages on their heads. In this drawing by Cobb, it’s amazing what a sense of motion you get from a still image made in a decidedly pre-youtube era.
Here ends our journey. If you are interested in reading the document whence these images came, you may unfortunately have some trouble as the USDA servers seem to be spotty lately. Here is a link to the original, and here is a link to a Google cache of the document.
Before I go, I want to share one additional gem — a meta gem — that I stumbled into as I was writing this post. To my delight and surprise, I discovered that in the same year — 1914 — Cobb had described marine nematodes collected on one of Ernest Shackleton‘s Antarctic expeditions (most likely the 1907-1909 Nimrod expedition, *not* the more famous Endurance expedition).
This is the magnificent, slightly repulsive Art Nouveau-cum-Nematode fantasia on the cover of that Journal of Nematology.
Did you see the cryptic words above “Nematology”? In contrast to Cobb’s elegant etchings, this might be considered a bit … er … baroque. But still fascinating, nonetheless.
As you may have guessed from the DENTE and the captions in this post, Cobb was also a gifted science writer. I leave you with his description from “Antarctic Marine Free-Living Nematodes” of what he found in the samples from Shackleton’s voyage. The nematodes of the Frigid South, it turns out, stand in marked contrast to the many “monsters” we saw above.