Sessile peritrichs are ciliates that achieve a more settled lifestyle than most other protists by attaching themselves to something more stable than they are. Spirally arranged rows of cilia encircling their disk-shaped front ends create powerful little vortices in the water and draw food particles to their mouths. Many of the sessile ("seated") peritrichs, like Vorticella, grow stalks (Leeuwenhook called them "tails") that anchor them in place. Telotrochs are what peritrichs turn into when they need to move.

Half the population needs to move once reproduction is accomplished—two daughter cells can share the end of a stalk for just so long, and then one has to leave. When there's too little food or some other undesirable situation nearby, adult peritrichs can make themselves into telotrochs and swim away. Then they grow stalks and settle down again. Usually.

This process is fascinating, but it's also problematical for us because the telotrochs don't necessarily look like the sessile peritrichs they once were. Several common species of Vorticella that look like those daughter cells elongate themselves considerably when they're traveling; as such they lose their familiar, identifiable bell shape. Further, they seem to contract themselves even more often than when they're sessile, and sometimes they stop and wriggle, so there's not even one cylindrical outline to watch for.

The telotrochs above were 80 µm long and 25 in diameter. Another species—with a lumpier body when sessile and more finely granulated cytoplasm than these—were 95 to 100 µm long and about 35 in diameter. A third, with a more tapered body when sessile and transverse "lines" visible on the telotroch, averaged 110 µm by 65. All these telotrochs were very strong swimmers; the first two kinds wobbled only slightly around their long axes while the third didn't wobble at all, and all three moved through the methyl cellulose on my slide as if it weren't there. In this regard they remind me of Didinium, which swim at "normal" speed in a methyl cellulose solution that renders Paramecium almost immobile. But then, Didinium have a high-energy diet, and the Vorticella telotrochs are what they are for swimming.

As I was watching, one telotroch either attached its rear end to the slide or else somehow held its rear end still while its front end rotated 360° around it for about 30 seconds; then it resumed swimming. What I'm calling the "front end"—with the rounded extrusion and the longer cilia—is actually the rear end—where the stalk was—on the Vorticella when it is sessile. When the organism transforms for swimming, the former rear end grows cilia and goes first. That rotating telotroch must have been using its peristome to hold on while it whirled itself around. Very strange: if the original peristome hadn't closed up when the organism became a telotroch, it could have created some suction, holding it to the slide, while the telotroch-front-end just kept on swimming (as Lacrymaria's "head" swims around and stretches the organism's "neck" amazingly). (1)

When telotrochs contract and wriggle, they cause interesting things to happen to their pellicles. Contraction affects the rear end more than the front; a good, strong contraction puts accordion pleats into the posterior half of the telotroch.

When they wriggle energetically, telotrochs bend their bodies to the degree that faint little striations appear on the side toward which they're bending. This implies that the front of the telotroch is not so elastic as its other end.

It's understandable that, up front, teletrochs are not quite the shapeshifters that they are farther back. The front of the telotroch, when it used to be the rear of the sessile zooid, needed only to contain cytoplasm and connect the contractile stalk to the contractile peristomal area; that part of the pellicle itself did little contracting or expanding. Those wonderful accordian pleats in the pellicle of the telotroch's posterior half have just the opposite history.

When a sessile Vorticella's stalk contracts, its peristome changes shape markedly. The "lips" from which the cilia grow contract when the stalk does, pulling the cilia inside the "bell." Instead of being aligned back to front, as they are normally, the cilia are turned 90° and point toward the center of the circle defined by the "lips"; depending on how long the cilia are and how strongly the organism contracts, their ends touch or even overlap. Meanwhile, the pellicle that was just below the peristome when the Vorticella was extended contracts and virtually closes, like the draw-string closure of a laundry bag. When this region becomes the rear end of a telotroch, it retains its elasticity and can easily fold into those accordian pleats.

To reach the conclusion that the front end of the telotroch is essentially featureless took me a while. Don't the cilia seem to demarcate a little "head"? And, especially when the critter is wriggling, doesn't it look like it's rooting around for food? But watching a slide full of teletrochs that had 20 minutes earlier been bell-shaped Vorticella and looking at them closely enough to draw them convinced me. The organelles of the sessile zooid stayed where they had been (see the contractile vacuole, the macronucleus, and the food vacuoles in my drawings all clustered in the telotroch's rear end). However cute a "head" a telotroch may appear to have, it's all in the eye of the observer: the blank "face" is just a remnant (or precursor) of the bell-shaped Vorticella's stalk.

Aside from my misinterpretations of what I'd been seeing and a little bit of anthropomorphism, I had some reason to delay my conclusion about telotrochs. In books that mention and picture telotrochs at all, there's no sign of the cilia that I've seen on their rear ends. Jahn depicts the formation of a telotroch in these five stages (Figure 444 in How to Know the Protozoa):
 

Kudo's depiction (in Protozoology) includes two earlier stages and the magic words "in vitro." So these are "test-tube telotrochs" (sorry; I couldn't resist), and different conditions may produce a somewhat different sequence. Of course, I didn't notice that qualifying phrase in Kudo's caption the first time I looked at the drawing, but once I did, it became a source of consolation. The telotrochs I'd been seeing were variants, that's all. And different species of Vorticella—as well as different genera and families of peritrichs—would probably include other variations.

Another conclusion I still have difficulty affirming is that free-swimming peritrichs don't use peristomal cilia for locomotion. The organisms to the right may or may not be telotrochs. They'd been so numerous on many of my slides that, before I learned to use methyl cellulose to slow down swimming micro-critters, I thought they were a new kind of protozoon. Then I recognized them as Vorticella without stalks, read what I could find about them, and began my acquaintance with telotrochs.

I learned how peritrichs leave their stalks behind to swim to a better location, how they'd change their appearance, how their peristome wasn't apparent anymore, how they grew cilia on their rear ends, and how they used these new cilia to get around. Trouble was, the organisms in this drawing weren't explained by what I'd been reading.

Then, for two months last summer, the water I collected contained large populations of peritrichs. And if one perseveres ... yes, I found a Vorticella changing unmistakably into a telotroch! As I watched, the little stalk-nub smoothed over, the cilia around it grew, and the peristomal cilia ceased motion; the new cilia clearly began to move the organism.

Still, the telotroch above became detached from its stalk before its new ring of cilia became operative. Although I had not seen it swimming before I watched its new cilia grow, any traveling it did before I came upon it had to have been done by its peristomal cilia. I've since seen stalkless Vorticella and Epistylis swim by using just their peristomes, and I've even found a Vorticella with none but peristomal cilia towing its stalk behind it and, behind that, a small bit of the substrate to which it was still attached. The inevitable conclusions are (1) Vorticella do turn into textbook-variety telotrochs, and (2) with or without their stalks, if they don't have trochal (posterior) cilia they can get around quite well by using their peristomes.

These were satisfying, but I still didn't know what those two free-swimming, maybe-telotrochs were. In light of what I'd been reading and then, from observing the Vorticella just discussed, I still had no explanation for the abundance of stalkless peritrichs that lacked telotroch characteristics. It's a good thing I had lots of peritrichs in my water jars.

The many peritrichs quickly taught me that my earlier identification of the "new kind of protozoon" as a stalkless Vorticella had been more comforting than accurate. No doubt some of them were Vorticella, but others could have been the colonial peritrichs Epistylis, Carchesium, or Zoothamnium, or the solitary Apiosoma or Campanella. (2)

To the right is their taxonomy. Below are outlines of their typical shapes with false colors indicating the distinctive arrangements of the filaments inside their stalks.

(Peritrichs' contractile stalks don't have myonemes inside them anymore. As the elastic fibers are made of the protein spasmin, not acto-myosin, the stalks contain spasmonemes.(3))

Vorticella are independent, each zooid having a contractile stalk entirely to itself. The individual organisms are nevertheless gregarious, usually found in the company of others. Carchesium are colonial creatures that share stalks. Within the shared stalk, however, each Carchesium has its own elastic filament (the more intense colors, above) that enables it to contract (see the bottom zooid) without causing the other members of the colony to contract with it. Zoothamnium are colonial and share stalks, too, but the elastic filament of each zooid is connected to those of the others; when contraction occurs, the elastic fibers pull all the organisms toward the site where the stalk is attached to the substrate (all zooids shown are extended). Epistylis are colonial, with stalks joined to those of other members of the colony. But since their stalks contain no elastic fibers, contraction affects only the individual zooids (in the drawing, half are contracted).

With Apiosoma and Campanella each individual has its own, non-contractile stalk. Apiosoma's stalk can be detected, usually, only with an electron microscope. Thus, while I've never knowingly seen any members of this genus, the invisibility of their stalks may account for the two stalkless peritrichs shown above. Or maybe not. The pair are definitely not Campanella, for the peristome of this genus is ciliated much more heavily than the other peritrichs I've mentioned, and the organism is usually noticeably larger as well. (More about Campanella later.)

From what I've been able to find written about them (4), I removed Carchesium from suspicion; they don't become regular teletrochs.

If this pair I watched were Carchesium, both daughters grow stalks that separate them within the colony.

If not Carchesium, they were probably Zoothamnium because of how common the latter are and because I didn't find members of other genera that were colonial with at least somewhat contractile stalks. (When I was watching them reproduce, they were under a coverslip; otherwise I could have poked them gently and let their response identify their genus.) The likeliest suspects thus became Epistylis. (5)

Reading, I learned that Epistylis are not monomorphic as Carchesium are, that they do have a teletroch stage. Observing, I noticed things that began to draw my questions and tentative conclusions together. For one thing, unlike Vorticella, the free-swimming Epistylis I watched were fatter than sessile ones.

These Epistylis (probably E. niagara), their relative sizes scrupulously shown, were drawn from a number of individuals. The sessile one (left) was 78 µm long, 35 µm at its widest diameter. The others are side- and from-the-top views of a free-swimming zooid that was 60 µm in diameter and 28 µm thick (peristome to scopula, where the stalk attaches); others ranged from 40 to 65 µm in diameter, and all were manic swimmers.

Trouble is, I had not seen Epistylis change from one form to the other, nor did I see a second, posterior row of cilia on any of the fat-bodied swimmers. But I did see the "centrally located scopula on [the] aboral pole of [the] telotroch," (6) visible in the drawing to the right. And, like the tube-shaped Vorticella telotrochs, these Epistylis zooids were very fast, strong swimmers. I can't be sure that they were Epistylis telotrochs, but the likelihood is greater for them than for the other, mysterious Epistylis swimmers.

While I had not seen any Epistylis transform themselves into the telotroch form shown above, I had been seeing many peritrich swimmers that I thought were Vorticella; less ignorant about peritrichs, I began to find numerous Epistylis that weren't fat telotrochs but that lacked stalks, like this one.

It had the identifying three turns of peristomal cilia, extra "lip" or "collar" just below the peristome, and long, curved cytopharynx or gullet, just as stalked Epistylis on the same slides had. Besides the presence or absence of a stalk, the chief difference between them was that the free-swimming zooids remained a bit contracted, slightly longer front to back than they were in diameter (125 x 95 µm). When these swimmers truly contracted, pulling in their peristomal cilia, they were only 100 µm long and fully 110 µm across.

Here are the same stalks and zooids as are in the drawing of Epistylis' outline and stalk configuration above.

Notice how the zooids seem too large for the stalks. I thought I'd drawn them wrong, and I double-checked.

The proportions are correct; while it's usually silly to make judgments about the way other living things look, in this case the anthropocentric "reflex" can be made to serve a purpose. Epistylis "bells" and stalks are, it seems, connected tenuously enough that the "bells" break free with relatively little provocation.

Thinking back on the peritrichs I had transferred from my water jars to slides, I realized that (1) looking at the colonies in the jars with my stereo microscope I saw few if any of the stalkless zooids; (2) transferring colonies of Carchesium and Zoothamnium to slides and observing them with my compound microscope, I found only a few of the stalkless and trochal-cilia-less organisms; and (3) doing the same to colonies of Epistylis resulted in hordes of stalkless zooids that used their peristomal cilia to move about.

So, I knew what the telotrochs of some species of Vorticella look like, and I knew what the fat telotrochs of some species of Epistylis look like. If I had to, I might be able to differentiate stalkless Vorticella from stalkless Epistylis swimmers by counting the rings of peristomal cilia (Vorticella have two, Epistylis usually have three) and noting the shape and length of their cytopharynges (Epistylis have longer ones with two bends). But I didn't have to—I couldn't even had I wanted to—because my supply of peritrichs had run out and the habitats from which I collected them had changed with the coming of cooler weather. The peritrichs gave way to other micro-life, like rotifers....

In November, amid exposed rocks below the small (six feet high) dam on the slow-moving Lost River, I took water from two isolated pools in the streambed. The river was much lower than I've ever encountered it, and I had no idea of what life it was harboring. Green life: desmids, green hydras, crustaceans and rotifers with green bellies. At home, once the water had settled a bit, I used my stereo microscope and found a large, golden-green rotifer.

After I transferred it to a slide, I saw what you noticed right away: the 250-µm-long "rotifer" was a gigantic peritrich. Its body was 170 µm in diameter, and it had a 110-µm-long stalk of refractive, crystalline blue, at the end of which was a holdfast still attached to a piece of substrate. It was relatively motionless, contracting itself occasionally so that its peristome was only 110 µm in diameter, then extending its long peristomal cilia and ingesting whatever they brought into its cytopharynx. This was a beautiful Campanella umbellaria, a big "stentor" of a peritrich, so large that the transverse marks on its pellicle were visible ("lines" 3 µm apart). I could see how the cytoplasm was denser at its posterior end, and how, on the right and left sides of its body, a similar darkening occurred where the illumination had to pass through more pellicle than it did nearer the middle.

Even the spasmonemes showed as faint lines radiating from where the stalk attached, upward and toward the organism's sides. (So they are the means by which peritrichs contract themselves!) At the end of the cytopharynx food vacuoles formed, about 20 µm in diameter, and moved counterclockwise, becoming smaller as digestion proceeded. The contents of the food vacuoles contributed to the organism's overall color, but the green hue was established by numerous small zoochlorellae: the size of this Campanella allowed me to see clearly that they were not enclosed in food vacuoles but were circulating in the cytoplasm. The size of the organism also revealed the extra "lips" at the base of the peristome. I wasn't able to determine how many rows of peristomal cilia there were, but (again, because of how big this organism was) I could see that there were more than three. I could also see that extension and contraction did not affect the shape of this Campanella except from its "lips" forward, where the cilia changed from being almost mesmerizing in their graceful motion (peristome extended) to appearing very much like an unruly haystack when the peristome was not quite fully contracted and individual cilia were oriented in every possible direction.

I found two other Campanella on the slide, one 200 µm long, the other 190. Neither had stalks. The smaller one had remained in the same vicinity, apparently, since arriving on the slide. It had moved, using its peristomal cilia, slowly and steadily, in the same direction —there were twenty-two bits of excreta, each clump equidistant from the others, and all in an almost straight line! After counting them, I checked back on the first Campanella—the one I drew—checked back just in time.

The big Campanella had trochal cilia! They were barely visible, 6 µm long, growing along the border of the denser cytoplasm near its posterior end, 30 minutes after I'd pipetted the organism from my water jar onto the slide.
 

At 40 minutes, the cilia were 9-12 µm long; the stalk was still blue, but less vibrantly so, and it looked as if it were breaking into segments.

At 50 minutes, the trochal cilia reached a length of 15 µm.

At 60 minutes, the cilia were still 15 µm long; the stalk was still intact but more nearly light gray than blue. Using both trochal and peristomal cilia, the Campanella began to swim very, very slowly.

At 93 minutes, the cilia were 23 µm long. Becoming a proper telotroch, the Campanella dropped its stalk, which had become grayish but remained intact. It had taken more than half an hour to travel 415 µm, not even twice its own length.
 

At 2 hrs 11 min (½ hr later), the trochal cilia were gone and a new stalk was growing: 22 µm long and 22 µm (the old stalk had been 15 µm) in diameter.

At 2 hrs 40 min, the new stalk was 46 µm long and 15 µm in diameter.

At 2 hrs 55 min, it was 84 µm long.

At 3 hrs 25 min, it was 100 µm long.

At 4 hrs 25 min, it was 156 µm long; new trochal cilia (20+ µm) had appeared.
 

At 6 hrs, the stalk was 165 µm long and no longer attached. The Campanella had grown a new one that was 30 µm long and, like the previous one when it was short, that looked very much like a tail. Neither of these stalks had a holdfast. Both were mostly transparent, without any refractive color. This time (4½ hours, from when it had detached from its first stalk) the Campanella had traveled 750 µm.


With this Campanella, the growth of trochal cilia caused or stimulated the disconnection from its stalk; or, at least, this organism didn't drop its stalk until the cilia on its rear end were near their maximum length and already active. Apparently, the which-comes-first question doesn't have a sure answer. Writing about Vorticella in 1998, two University of Illinois biologists say that the stalked zooid "undergoes a morphological transition to the cylindrically shaped, motile telotroch [which] then detaches from the stalk and swims away." (7) When they report their "chemical induction of telotroch formation utilizing monocalcium phosphate," however, they reverse the sequence, noting that "[s]talk severing, which precedes telotroch formation, is induced at pH 3.2" but not in a less acidic environment. Thus it seems that either growing trochal cilia or disconnecting from its stalk can be the initial visible sign of a peritrich's transformation into a telotroch.

Remembering that Epistylis teletrochs seem the result of the stalked zooid's having been squashed from front to rear and that Vorticella transform themselves into "cylinders" that look considerably longer and narrower than the zooids were while sessile, I was probably expecting the Campanella to alter its shape. To the right is how the telotroch typically looked.

If you look closely, you can see how the organism's squared-off or rectangular appearance is mostly an optical illusion: when the trochal cilia flick out, they create a "corner" that sustains the illusion, which is reinforced by the peristomal cilia's no longer being extended in a series of regular, graceful lines. But the difference in shape between the Campanella with a stalk and peristomal corona and how it looks when it has trochal cilia and no stalk is more apparent than real.
 

Here they are together: the Campanella immediately after it lost its stalk and the same critter several minutes later. Excluding peristomal cilia, both images are 59 pixels across. When I measured the images, the result was a surprise.

Of course, there is an actual, small change in shape. In the rear the scopula is pulled "in" or forward, and in front the peristomal cilia are no longer fully extended. The partial contraction of the whole organism accounts for both these results and also for the thickening of the body just behind the peristome. I'm sure there's a relation between this contractedness and that of the swimming, stalkless Epistylis I'd been finding, but I don't know what it is beyond the fact that neither those swimmers nor this telotroch had closed off their anterior ends the way that Vorticella teletrochs typically do.

This Campanella telotroch exhibited three forms: a "proper" telotroch form in which all the peristomal cilia were drawn into the anterior part of its body, a sessile-like form in which those cilia were fully extended, and a partly contracted form in which those cilia were, at least visually, in a state of disarray. Watching this Campanella, I couldn't suppress my judgment that it didn't know what it was doing —or, to use less subjective language, that it behaved as if neither the sessile nor the telotroch form was a satisfactory response to its environmental situation. When it had no stalk and was traveling (in its most compact form, with the trochal cilia moving it), the organism would nevertheless extend its peristomal cilia either part way or all the way every few moments; once the cilia were out and working, the Campanella was feeding. Particles were arriving in its cytopharynx and being packaged into food vacuoles even when its peristome was disarranged. Was the organism accumulating information about the availability of food in its current location? —certainly. Was it acting on the information? —who knows?

When I found it, the Campanella was 250 µm long and 170 in diameter; 4½ hours later it had lengthened to 280 µm (with the same diameter) and had grown 156 µm of new stalk. Its environment was providing enough food for survival, if not for reproduction. Would its new stalk attach to something only if the organism was stimulated to reproduce? I.e., if the vicinity was rich enough in food to give the Campanella enough energy to fission? Or is a glass surface something to which Campanella holdfasts simply don't attach? Before I can even reformulate these questions, I'll have to find some more Campanella and a way to culture them.

The next day, I found the big Campanella 750 µm farther along in its odyssey. It was 300 µm long and 145 µm in diameter. During my absence of 17 hours, it had grown stalks of 350, 135, 190, and 70 µm, and it had dropped the three long ones where I could easily reconstruct its route.

The Campanella had also dropped 13% of the volume it had when it arrived on the slide, and 23% of the volume it had 17 hours earlier. Its food supply had run out, and there probably wasn't much oxygen left (most of the slide's other occupants had succumbed to anoxia). But it continued to use its peristomal cilia and to create food vacuoles. In contrast to the day before, the vacuoles were practically empty. Probably, these food vacuoles were pinching off when they reached a certain volume irrespective of their contents. The area around the Campanella was relatively free of excreta; in fact, the little clumps were most numerous around the organism's first two positions (on the "trail of the telotroch" above) and gradually, in an almost even distribution, grew fewer in number as it moved on. Considering this pattern, the diminution of the telotroch, and the way those studied Vorticella were made to sever their stalks electro-chemically, I wonder if there isn't a relation. Since digestion changes the pH of food vacuoles, the Campanella may have become a telotroch as a response to the the water in the immediate vicinity of its excreta. Reaching somewhat "better" water, it grew a stalk. Then it responded to the lack of food in the new location by growing trochal cilia and dropping the stalk, and then it responded to the still "better" water by growing a new stalk, and then to its "still hungry" condition with new trochal cilia, and then.... —No wonder the critter was losing weight!

It was still quite a beautiful "animalcule." It had provided particularly easy-to-see illustrations of telotroch morphology and behavior, some of which I've already been able to relate to subsequent sightings of smaller, less revealing telotrochs. Responding to the excellent observations it had afforded me, I gently rinsed both slide and coverslip into the water jar, where, I hope, the Campanella found something to hold fast to and many little somethings to eat.

Notes

(1)    See "Tears of a Swan" (Micscape, Feb 98) for a detailed look at Lacrymaria olor.

(2)    Kudo (in Protozoology) says of all Epistylids that "individuals [are] usually on dichotomous non-contractile stalks, forming large colonies" and of Campanella umbellaria only that four or more turns of oral ciliature distinguish it from Epistylis. All those I found were solitary, and the Protist Databases web site describes Campanella as either "solitary or colonial."

(3)    Richard Fox, in the Vorticella section of his "Protozoa Laboratory Exercises" web site.

(4)    D. J. Patterson's description of the genus on the micro*scope web site describes Carchesium as monomorphic, which I interpret to mean they have only one form, the sessile one. Zoothamnium's description says that only some of the colonial species are polymorphic. I use the words "regular telotrochs," however, because Carchesium and Zoothamnium that become detached from their stalks must use their oral cilia to swim. But Kudo (in Protozoology) says of the peritrichs in general that those with stalks produce swimming, teletroch forms. Patterson's work postdates Kudo's and Jahn's (who lists both Carchesium and Zoothamnium as epistylids); moreover, it lets me get on to Epistylis.

(5)    This all gets pretty complicated and leads to the question / conclusion, "Aren't we glad we're amateurs?" The case in point is the formation of colonies. If, after reproduction, half the daughter cells of Carchesium, Zoothamnium, Epistylis, and the other colonial peritrichs turn into telotrochs and swim away, how these genera form colonies of many individuals attached to one another by stalks is a question left unanswered. On the other hand, if the zooids remain attached to their colony after reproducing, there should be only one monstrous colony of each instead of billions of colonies worldwide. Sexual (rather than asexual) reproduction doesn't solve the problem, since it still results in new zooids that have to swim away or stay attached. Now, if sexually-produced new cells did one thing and asexually-produced ones did the other ... But even this answer doesn't account for the zooids that get detached from their colonies. Somehow I doubt that nature is so wasteful as to relegate these critters to a premature end (especially since they can eat and swim; and they're hardwired to reproduce if they eat enough; and once they reproduce the question of what the daughter cells do—attach or swim—arises again). Of course, if another critter eats them their end isn't premature ... nor, from a detritovore's point of view, would it be if they died right after they were dislodged from their stalks (but they don't). Ü

(6)    Patterson, the micro*scope web site page on Epistylis.

(7)    P.J. Debaufer and H. E. Buhse, Jr., "A Possible Mechanism for Initiating Stalked Zooid to Telotroch Transformation in Vorticella," Proceedings of the 51st Annual Meeting of The Society Of Protozoologists, August 1998.