Sunday Protist - Euglyphids

by Psi Wavefunction in Skeptic Wonder

I'm going to be lazy and leech off the Mystery Micrograph again. None of you saner people (non-protistgeeks) seem to have taken advantage of the massive handicap, and subsequent hint. Seriously, type in "testate amoebae" in Google image search, and it's on the first page! Perhaps I should do a tutorial on some methods of attacking those mystery images...Quite shockingly(not!), Opisthokont got the last one. I agree with his statement that that was like shooting fish in a barrel, but easier since fish are actually difficult to shoot at from air due to refraction, etc. The organism behind the shell in the mystery micrograph was...Euglypha!(Wikipedia; Euglyphid test)Euglypha morphologically belongs to the polyphyletic 'testate amoebae', but is phylogenetically quite distant from your garden variety test-building amoebozoans, like Arcella and Difflugia. Euglyphids are cercozoan rhizarians. Since those words likely mean nothing to the vast majority of the human population, here's a 'map' of Rhizaria in my Coelodiceras (Phaeodaria) post, and an overall tree of eukaryotes can be found here. They can often be found in moss samples, but are also present in soil and freshwater environments. Their test scales are made of silica, and preserve quite decently as fossils. Speaking of which, I apparently may have a slight fetish for unicellular microfossils:(Javaux 2007 in Eukaryotic Membranes and Cytoskeleton: Origins and Evolution ed. Jékely; 10 - fossil; 11 - modern Euglyphid; 12 - VSM - 'vase-shaped microfossil' (micropaleontological equivalent of mycologists' LBM - 'little brown mushroom' ?) with holes possibly caused by predation; fossils ~750My old)Fast forward 750My back to the present, the modern euglyphids are about as diverse as they are understudied:(Lara et al. 2007 Protist; tree of Euglyphids)Images of Euglyphid diversity, shamelessly stolen from the same paper:(Lara et al. 2007 Protist; Euglyphid SEMs, scalebar 50um except for E,F,H, where it's 10um. A - Assulina; B- Placocista; C,D - Euglypha ciliata & compressa; E - Corythion; F - Trinema; H,G - Euglypha penardi)Unfortunately, finding nice plates full of euglyphids is rather difficult, since until quite recently, they were lumped together with testate Amoebozoans. Also, since euglyphids fossilise, they seem to be mostly studied by paleontologists, who seem to have an 'interesting' relationship with systematics of the living. Where 'interesting' entails being at least a couple decades out of date. Well, they are millions of years in the past...Paulinella can be argued to be particularly interesting - it is a case of an independent event of primary plastid endosymbiosis. Why this is interesting can be seen in this really nice overview:(Keeling 2oo4 Am J Bot (free access); overview of plastid endosymbiosis - the 'Pacmen' are pretty awesome! Interestingly, if the Chromalveolate Hypothesis is correct, this would mean that Paulinella already had a plastid in its ancient past. However, it would've been a red algal plastid of a different cyanobacterial origin, not a Synechococcus-derived cyanelle)Cyanelles are photosynthetic endosymbionts/organelles - they differ from plastids by retaining some prokaryotic features like the peptidoglycan wall. Among the conventional plastid-bearing algae, glaucophytes carry cyanelles from the primary cyanobacterial endosymbiotic event which eventually led to plant chloroplasts and most algal plastids. In sequence comparisons, Paulinella cyanelles branch with the cyanobacterium Synechococcus, and retain much of the gene order, suggesting a fairly recent endosymbiosis with Synechococcus (... Read more »