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On water fleas you often see micro-organisms, sometimes so close together that the water flea seems to have a coat. In the three Simopcephalus specimens above they are not that dense. Click on one of the pictures for a larger photo. The micro-organisms here are sessile pertirichs. According to Streble & Krauter (1973), on waterfleas this is often the species Epistylis digitalis. However, that species has clearly ribbed stems, which is nowhere to be seen in the photos on this page. Another species is E. plicatilis, but the cellbodies of that species should wrinkle quite strongly on the underside when they retract, which is also nowhere visible here. On the web, including on the site of the NIES (see literature), you can read that there are many species. Fish, e.g. goldfish and Koi, can also be covered with Epistylis species. This type of pertirichs probably benefits from the mobility of their hosts, by a larger supply of food particles, also because the small crustaceans and fish they sit on will whirl up those particles. Although Epistylis peritirchs are not parasites, fish often seem to get a bacterial infection (or it is already present) and that may then be fatal. It is of course interesting whether these protozoans, when present on the water fleas, might get transferred to the fishes, but I have not been able to find any article on that.
Sessile peritrichs, sometimes called bell-animalcules, are unicellular organisms, see Vorticella. As with Opercularia species, which occur on water insects, the main difference with Vorticella is that the stems are not contractile. Epistylis digitalis is also said to occur on copepods, such as Cyclops species and indeed I have often seen (unidentified) peritrichs on them, see the pictures below.
The picture above left is a microscope photo of the bell animals on a Cyclops crustacean, the dark red spot is the eye. The pictures above right are from an older macro photo, only to show how the left photo is situated, so it is not the same Cyclops specimen. At the same time, that comparative photo shows that these peritrich organisms become too small to be clearly visualized without a microscope. The eye of the crustacean is depicted striking red, due to the incident, instead of transmitted, light.
Below are some more microscope photos. Click on the pictures to see larger images.
There are two short microscope videos, which can be viewed by clicking on the pictures below.
Like most sessile peritrichs, Epistylis can detach the cell from the stalk and swim freely until a new location is found. There the cell then makes a new stalk. This possibility is of course a great advantage, for example in the event of the death of the host.
Literature: (See also: Bibliography microscopic organisms).
Streble,H & Krauter, D (1973) Das Leben im Wassertropfen.
Kosmos Gesellschaft der Naturfreunde.
Franckh'se Verlagshandlung Stuttgart 1978. (75-76 en 246-247).
The World of Protozoa, Rotifera, Nematoda and Oligochaeta
The National Institute for Enviromental Studies (Japan),
read 16 apr 2024 on: https://www.nies.go.jp/chiiki1/protoz/morpho/ciliopho/epistyli.htm
