Bicosoecids were shown off fairly recently- but wait, there's more! One particular pond sample was rich in colonial bicosoecids whose loricas were conveniently accentuated by a touch of iron (rusting). In iron-rich samples, some protistan creations (organic tests and loricas) turn browner with age as iron oxides accumulate. So if you've ever wondered whether protists rust... now you know.
They're kind of addicting to photograph. Evidently, Haeckel (1904) thought similarly about engraving them (figure 10 in Plate 15)
Bicosoecids aren't the only protists who build loricas -- in fact, house- or cup-like structures are fairly popular throughout the eukaryotic world. Take this choanoflagellate (Diploeca sp.), for example, sitting in a flask as it waves its flagellum to draw in bacteria to meet their doom.
Or the Jakobids (excavates, notable for having the most complete mitochondrial genomes -- ie, seemingly having retained the most genes from the original bacterial symbiont mitochondria come from): Histiona sp., and -- I'm not making this name up -- Reclinomonas americana, genus aptly named for the flagellate's appearance of reclining in its lorica as it 'lazily' waves about its flagella. Reclinomonas went an extra step and covered its lorica with nail-like scales -- facing outwards, of course -- which are marginally noticeable in its photo below.
Some ciliates build themselves flasks and bottles too; for example, folliculinids, which I have written about on my other blog. Lagynion is an obscure chrysophyte alga also sitting in a bottle, though a much more common relative, Dinobryon, builds massive tree-like colonies similar to those of the bicosoecids above. This is by no means a comprehensive survey of bottle-dwelling protists!
These structures provide some protection from predators as well as general mechanical events (eg. you stepping on their microhabitat -- yes, we're all continuously guilty of that!). When in danger, or when tired, perhaps, the protists withdraw themselves into their respective vessels, and wait. Once again, our size as animals might be worth appreciating a little -- imagine walking around in the woods with menacing critters and their flagella jumping out of cryptic pots!