Sunday Protist - Litostomatea: rumen ciliates with incredible morphology

Scary lab exam in 9h, so this one will be another 'protist appreciation' compilation rather than anything particularly informative. Today this maltreatment will be inflicted upon some poor ciliates, which deserve much more than just a simple appreciation post. Ciliates ARE the higher eukaryotes, the most advanced and awesome organisms on earth. What god created in his/her/its image wasn't the ugly naked humans, it was, in fact, Spirotrich ciliates. Everything else is just basal offshoots, failed experiments. This is an unbiased, objective opinion with piles upon piles of supporting evidence. 'xcuse my word choice, but ciliates are fucking awesome.

Complex shapes in multicellular species aren't particularly amazing, as intricate self-organising properties can arise in populations even without any attemps at coordination (eg. [some?] bacterial swarming). A thing with 10¹³ own cells exhibiting complex morphology isn't all that amazing, especially as many of the architectural principles are simply repeated over and over again. What IS truly amazing, is when a unicellular organism can achieve complex shapes* like these rumen denizens:

Some horse rumen gut Litostomatea from Stueder-Kypke (2007 EJP) The thick black thing in the drawings is the macronucleus (MAC).

As you can see, they're quite diverse and...weird. These Litostomateans live in digestive systems of various animals, mainly rumens of cows, sheep, horses and the like. They're microaerobic (since there's still trace amounts of oxygen in the gut), and some seem to even have hydrogenosomes (modified mitochondria). There's also some interesting flat ones found in Australian marsupials, with a weird mesh pattern on the left and right sides:

Macropodinium; also contains endosymbiotic bacteria just under the cilia. (Cameron & Donoghue 2002 EJP)

A brief tour of the anatomy of an arbitrary Litostomatean ciliate is in order. Let's oogle in awe at the complex morphology of Eudiplodinium, from Furness & Butler 1985 JEM**:

Let's start with osmotic regulation, the ciliate equivalent of excretory system, if you will. The two blobs labelled CV are contractive vacuoles, which tend to be common (if not obligatory) among freshwater organisms. I'd imagine the rumen would qualify as closer to freshwater than marine, so that's probably why Eudiplodinium has them. The contractile vacuole itself is a complicated structure, consisting of ducts (which drain the excess water, somehow), a central 'bladder' equivalent with a channel leading outside, and subcellular 'muscle' equivalents responsible for vacuole contraction.

Then we have the germline micronucleus(MI) and somatic macronucleus(MN) (the substantially bigger one); I've explained this recently towards the bottom of this post, and I'm being really lazy right now. Go read about it there, or in the introduction of this report. Or this post from the Catalogue of Organisms.

The DZS and AZS are dorsal and adoral zones of syncilia, respectively, where clumps of cilia like those in the first figure appear. The adoral zone happens to be near the peristome (mouth), and may thus likely be involved in feeding. The dorsal zone could be involved in motility perhaps? The paper seems to assume the reader knows this stuff, as it's more of a cytomorphological description; although to be honest, I haven't actually read the entire thing.

Speaking of the peristome, next we have a subcellular analogue of a digestive system - the cytoalimentary system - consisting of a ridiculously complicated cytopharynx (mouth and throat, if you will) leading to the endocytoplasm, where the prey or food particles are packaged into vacuoles and digested alive. And the secreted out the cytoproct, or 'cell anus', if you will. In fact, here's what the menacing cytopharynx looks like in detail (again, from Furness & Butler 1985 JEM):

The structures marked by L at the top are the cellular equivalent of lips. Another point for ultimate convergence. 'Primitive organisms' my ass.

The cortex, or 'skin' of the organism is no less menacing structurally. Especially around the cilia. First off, ciliates belong to Alveolata, which are characterised by having alveolae, or small membranous sacs just underneath the plasma membrane. These structures are often modified to contain protein secretions building up structures like armour plates. Probably have other functions too, I just don't know very much about them at this point. Now when you add rows and rows of cilia to that, you get a convoluted maze of basal bodies, the cytoskeleton and various fibrillar and endomembrane networks 'servicing' the entanglement of cilia. I found a really nice example for a relative of Eudiplodinium, Epidinium, from Furness & Butler 1983 JEM:

I should probably get back to cramming studying soon, so let's just leave it at that: It's complicated. If only cell structures had Facebook relationship statuses...

You've probably had enough of Litostomatea for now, if such a thing is possible. So we'll wrap up here. As for their phylogenetic neighbourhood, here's my simplified version of Lynn 2003 Eur J Prot diagram (branching depth not to scale):

Litostomatea are the third from top. As a tiny sample of how wonderful ciliates can get: Spirotrichs include 'walking' ciliates like Euplotes and Stylonychia, some of which are famous for 'scrambled genes' (see figs 3b,c of this report); Colpodea which include the giant Bursaria(really nice gallery, btw); Heterotrichs, incl. the giant (1-2mm!) trumpet-shaped Stentor*; Oligohymenophorea with the familiar Paramecium and Tetrahymena(NSFW); Armophorea with the amitochondriate Nyctotherus; Phyllopharyngea with Chilodonella and suctorians like Ephelota with its really neat branching MAC; and lastly, amitosis-lacking Karyorelictids with Tracheloraphis and Loxodes. Overall diversity summed up nicely in this striking picture. Eventually I may explore some of these in detail, as what I've done here is rather offensive.

Hopefully you are slowly nearing Enlightenment, wherein you will realise that ciliates are the higher eukaryotes, and the awesomest organisms on the planet. To supplement this process of personal spiritual growth, I recommend slapping some pond water or soil samples on a slide, and watching various ciliates running around, in the case of Hypotrichs -- literally. All hail our ciliate overlords! May your macronucleus forever be pure and contain a complete set of genes. On that note, be careful about conjugation -- procrastinate too long and you'd have to undergo autogamy. And nobody wants that.

*A certain Parabasalia fanatic asserts that hypermastigotes have the most sophisticated cell structure -- he could not be more wrong. Hypermastigotes merely took karyomastigotes and multiplied them over and over again in a spiral -- overwhelming in terms of flagellar number, but architecturally quite simple. Ciliates have a sophisticated assymetrical non-repeating cortical organisation, for one thing, and are much more complex on the genomic level as well. Parabasalians don't even have proper mitochondria, for crying out loud! I mean, even dinos are more sophisticated than Parabasalia. Dinos are the second highest eukaryotes. Are we happy now? (there's a war between ciliatologists and people who study dinos, and clearly ciliates are winning as they actually have a name for people studying them. Dinologist? Dinoflagellatologist? Ewww. See, clearly our side is winning. Dinos are just "free-living apicomplexans". Case closed.)

**JEM website: how I hate you for displaying the online publication date in a very prominent location on the abstract page for old articles, rather than their original publication date. Oh how often I get led astray, sometimes even confused, reading something from the long gone past thinking it was published last year. Sometimes I get excited thinking people still do quality cytology work as opposed to aligning sequences all day. I even get a glimmer of hope for humanity. And then I check the paper itself. And become heartbroken. That's just cruel.

References
CAMERON, S. (2002). The ultrastructure of and revised diagnosis of the Macropodiniidae (Litostomatea: Trichostomatia) European Journal of Protistology, 38 (2), 179-194 DOI: 10.1078/0932-4739-00861

FURNESS, D., & BUTLER, R. (1983). The Cytology of Sheep Rumen Ciliates. I. Ultrastructure of Epidinium caudatum Crawley The Journal of Eukaryotic Microbiology, 30 (4), 676-687 DOI: 10.1111/j.1550-7408.1983.tb05343.x

Furness, D., & Butler, R. (1985). The Cytology of Sheep Rumen Ciliates. II. Ultrastructure of Eudiplodinium maggii The Journal of Eukaryotic Microbiology, 32 (1), 205-214 DOI: 10.1111/j.1550-7408.1985.tb03041.x

LYNN, D. (2003). Morphology or molecules: How do we identify the major lineages of ciliates (Phylum Ciliophora) European Journal of Protistology, 39 (4), 356-364 DOI: 10.1078/0932-4739-00004

STRUDERKYPKE, M., KORNILOVA, O., & LYNN, D. (2007). Phylogeny of trichostome ciliates (Ciliophora, Litostomatea) endosymbiotic in the Yakut horse (Equus caballus) European Journal of Protistology, 43 (4), 319-328 DOI: 10.1016/j.ejop.2007.06.005