This colony of bell-shaped ciliates (unicellular organisms) has a blue appearance in the light of the flash unit. The hornwort in this photo was completely overgrown with these types of colonies. To the naked eye, the colonies look like tufts of fungus. The stems all seem to be separate on the plants, in which case it is not a real colony, but a group. If they are 'bunches' on a few larger stems, they could be colonies of a Carchesium species. Because this is difficult to see here, this possibility cannot be ruled out. The species pictured ar reletavely large bell-shaped ciliates: the cells measure roughly 200 µm, many stems at least 1 mm. The stems can be retracted like a corkscrew in a startle reaction, whereby the cilia are also retracted.

Vorticella systematically fall under the phylum Protozoa, one-celled organisms, also known as prehistoric animals, infusoria. Within that phylum they are in the class Ciliata, and within that in the order Peritricha. The prefix Peri- can mean 'around', but it could be equivalent to Latin circum- and then it is more correct. Because the cilia, the 'hairs' (the -trichida in the name) are in a circle on the upper edge. This is in contrast to the Holotrichida, which have cilia spread over the entire cell wall. The circle with cilia runs spirally towards the mouth, where the cilia have grown together into an undulating membrane. The hairs whip the surrounding water into a relatively strong eddy current towards the mouth, where food particles are taken in and unsalvagable particles are removed.

Vorticella often occur as free-swimming individuals. Two suborders are indicated: some species never attach themselves and fall under the Mobilina, but most settle on a suitable substrate (substrate) and are placed in the suborder Sessilina. At their rear end these Vorticella have the Scopula, a transformed cilia field without cilia, which separates the stem. Stems can be long or short, retractable or rigid. Vorticella can also detach themselves from their stem, to swim freely to another suitable place, where a new stem is formed.

Most of the data in the last two paragraphs above are from Streble & Krauter (1973).

Why would bell animals want to be 'stuck'? I have not found an explanation yet. Perhaps energy conservation? The force, which would otherwise have to be divided between propulsion and food retrieval, now fully benefits the retrieval of food. The stem provides a good anchoring, which allows the eddy current to be strong, which would otherwise propel and displace the animal. It is just my own idea...

Vorticella play a role in the 'reactors' of sewage treatment plants; according to Eisenman et al. (2001), in their study about 14% of the small particles were captured by an Epistylis species.

Literature: (See also the Bibliography Microscopic organisms).

Eisenmann H, Letsiou I, Feuchtinger A, Beisker W, Mannweiler E, Hutzler P, Arnz P. Interception of small particles by flocculent structures, sessile ciliates, and the basic layer of a wastewater biofilm. Appl. and Environ Microbiology 2001 Sep;67(9):4286-92.
doi: 10.1128/AEM.67.9.4286-4292.2001. PMID: 11526035; PMCID: PMC93159. Read 5 apr 2024.

Streble, H & Krauter, D (1973) Das Leben im Wassertropfen. Kosmos Gesellschaft der Naturfreunde. Franckh'se Verlagshandlung Stuttgart 1978. (75-76 and 248-249).