Nassulids -  Colourful Ciliates found
in Pond Water

(Nassula and Obertrumia sp)

by Dr. Robert Berdan
October 22, 2021

Above is a Nassulid ciliate, note the nucleus (N) and (C) the Cyrtos also called a nasse or pharyngeal basket which is used to feed on filamentous blue-green algae. Photographed with a Differential Interference Contrast (DIC) light microscope 100X.

     Nassulids belong to the class of Nassophoreans which are alien-like visitors from another world - the micro-world.  Nassulids are found in fresh water, brackish waters, marine environments and in moist soils.  They have an anterior mouth surrounded by a palisade of rods called nematodesmata that are used to feed. A light microscope is needed to observe these ciliates. This article focuses on a couple of nassulid species found near Calgary, Alberta.

     Ciliates are single celled-animals living in water on all continents. More than 8,000 species of ciliates have been described and it is estimated there may be more than 30,000 species. Most ciliates are not harmful and serve as part of the food web feeding on smaller bacteria, algae and detritus. In turn copepods and small fish feed on them. Ciliates share the common characteristic of having cilia or “hair-like” structures covering their bodies. Cilia propels these organisms and plays a role in their feeding and sensing their environment. Ciliates vary in shape, size and colour and many are able to swim quickly. There is a renewed interest in ciliates in trying to understand whether or not these complex single cells are capable of learning and whether or not they can form memories (S. J. Gershman et al., 2021).  Ehrenberg was the first to describe several Nassulid ciliates – see below (Ehrenberg, 1830).

Ehrenberg paintings of Nassula ornata and Nassula aruea (Obertrumia aurea) 1838

Ehrenberg paintings of A. Nassula ornata and B. Nassula aurea (now called Obertrumia aurea) 1830 source - see more of his early paintings.

Nassula sp of ciliate Darkfield microscopy Robert Berdan

Image above resembles Nassula ornata in the painting above by Ehrenberg - dark-field microscopy. A few strands of Oscillatoria are visible outside and inside the cell 100X.

Obertrumia aurea? ciliated by Robert Berdan ©

Above picture of the ciliate resembles Obertrumia aurea shown in the painting above. The colour of the cytoplasm varies from clear, orange and to pink in colour. 100X DIC microscopy.

Pink Ciliate by Robert Berdan ©

This ciliate has pinkish cytoplasm and a few Oscillatoria filaments are visible inside vacuoles. 100X DIC microscopy.


Domain: Eukaryota
Subphylum: Intramacronucleata
Class: Nassophorea
Order: Nassulida
Family: Nassulidae
Genus: Nassula, Obertrumia
Species: ornata, aurea, (Ehrenberg 1833)

Obertrumia aurea versus Nassula ornata - figure by W. Foissner 1994

Nassulid holotrichs drawings from life. 14 Obertrumia aurea 15 Nassula ornata, 16, 17, 18 Trichocysts of N. ornata. Ma macronucleus CV contractile vacuole, V blue vacuoles, B feeding basket, FV food vacuole, S synhymenium (adoral organelles) from W. Foissner (1994). Figure 14.

     I have been photographing and attempting to identify various aquatic micro-organisms living in ponds near my home in Calgary. I often visit ponds in Calgary north west (Bearspaw area) to collect pond samples (see map at bottom of page). The number of different species found in a simple pond is amazing. The taxonomy of ciliates is changing rapidly due to molecular biology studies of these organisms. The Nassophorea are a Class of ciliates characterized by a “nasse” or basket of microtubules that they use to feed on blue-green algae (cyanobacteria). The nasse is also called a cytopharyngeal basket or cyrtos and the rods can often be seen by focusing through the specimen. The nasse is a complex structure that has been studied using electron microscopy (J.B. Tucker, 1967, 1968, 1978). The rods are made up of microtubules which are used to pull filamentous blue-green algae (cyanobacteria) into their body. Blue-green algae have been around for billions of years and are credited with producing the first oxygen in our planets atmosphere. These filamentous bacteria-like algae have no nucleus that envelopes their DNA and some species are capable of movement.

Oscillatoria filament - blue-green algae or cyanobacteria by Robert Berdan ©

Oscillatora sp filament - this blue-green algae (cyanobacteria) is capable of movement and they are eaten by various ciliates. Pieces of the filaments can be seen inside the ciliates and vacuoles and their digestion results in multicoloured vacuoles inside the ciliates as shown below.

Nassulid species - ciliate with coloured granules by Robert Berdan ©

Nassulid species photographed with bright field microscopy showing an algal filament outside the cell and numerous fragments inside along with colourful vacuoles. 100X. All pictures are of live unstained specimens.

Nassulid species with Oscillatoria filaments in close proximity by Robert Berdan ©

Nassulid species with Oscillatoria filaments in close proximity. Bright field microscopy 100X.

Nassulid sp ciliated via Phase contrast microscopy by Robert Berdan ©

Nassulid photographed by phase contrast microscopy. The coloured vacuoles are not as apparent with this technique but the nucleus (top), four contractile vacuoles and the nasse are visible - 100X.

     What makes some nassophorean ciliates interesting is that when they feed on blue-green algae the break down products form coloured vacuoles and patches in the cytoplasm. The different colours and relatively large size of the nassophoreans is what first attracted me to them. Their vacuoles and lipid vesicles take on colours ranging from yellow, orange, pink and violet. The colour of the globules depends upon the composition of the pigments of the ingested blue-green algae (A. Brabrand et al., 1983). Those blue-green algae that comprise mainly phycobiliproteins result in blue-violet globules during digestion (e.g. Anabaena and Aphanizomenon) while those algae containing phycoerythrin pigments (e.g. Oscillatoria) produce brown or pinkish pigments (M.M. Carter et al. 1990).  Some species of nassulids (Nassula aurea, now called Obertrumia aurea also called Obertrumia georgiana) have been investigated as a means of biological control during blue-green algae blooms (Carter et al., 1990). Some blue-green algal blooms produce toxins that can kill livestock, birds and other animals.

Nassulid with coloured granules, the nucleus is near the left side next to the nasse. 100X DIC microscopy.  by Robert Berdan ©

Nassulid with coloured granules, the nucleus is near the left side next to the nasse. 100X DIC microscopy.

Cytoplasm at 200X shows pink and violet lipid-like vacuoles and vesicles. 200X DIC microscopy by Robert Berdan ©

Cytoplasm at 200X shows pink and violet lipid-like vacuoles and vesicles. 200X DIC microscopy.

Nasulide Oscillatoria filaments, vacuoles and part of the nasse is visible just below the nucleus. 400X DIC microscopy. by Robert Berdan ©

Above near the top center of the picture is the nucleus surrounded by Oscillatoria filaments, vacuoles and part of the nasse is visible just below the nucleus. 400X DIC microscopy.

Cytoplasm at 630X DIC microscopy showing an Oscillatoria fragment and several coloured vacuoles in the cytoplasm of a Nassulid ciliate.  by Robert Berdan ©

Cytoplasm at 630X DIC microscopy showing an Oscillatoria fragment and several coloured vacuoles in the cytoplasm of a nassulid ciliate.

Nassulid ciliate at different magnifications showing the coloured granules and vacuoles in this ciliate's cytoplasm. by Robert Berdan ©

Above are several views of a nassulid ciliate at different magnifications showing the coloured granules and vacuoles in this ciliate's cytoplasm (bright-field and DIC microscopy).

     When these ciliates are stationary their cytoplasm actively streams and resembles an abstract painting in motion. The streaming may be involved in producing “suction” which draws filamentous cyanobacteria inside. Cytoplasmic streaming also plays a role when these ciliates come out of their overwintering cysts (C.D. Beers, 1966). The ciliates are induced to form cysts by lack of food and the addition of bacteria makes them come out of their cysts. Unfortunately I have not yet had an opportunity to film these ciliates feeding on cyanobacteria, though I have links below to films that others have taken of them feeding.

Nassulid ciliates showing the multicoloured vacuoles and internal cellular compartments. Watch Movie on Youtube - musical background by Donna Berdan. Some views show a faint hypostomial frange (3 min 26 seconds).

     The nassophoreans I have come across so far appear to be comprised of various species of nassula - the larger ones are likely Obertrumia aurea. Their bodies are mostly ovoid in shape, they have a single macronucleus and their cells are between 100 to 300 microns (micron is 0.001 millimeter). The cells are capable of swimming at a moderate pace and often twist while swimming when viewed with a stereomicroscope.  The ciliates often slow down or stop when they encounter detritus or algae.  A large contractile vacuole is also visible near the nucleus of the cells and it excludes excess water that moves into the cell by osmosis - watch for the contractile vacuoles in the movie above.  

     It is possible to slow or pin these ciliates down by drawing water out from under the coverslip with a piece of paper towel. The coverslip then compresses and flattens the larger ciliates for photomicrography.  If however, the cells are flattened too much they burst showing their inside contents and whether or not they have extrusomes (trichocysts) which are defensive structures. Some species like Nassula ornata have trichocysts, but I was not able to see any after several cells burst suggesting they are a different species, possibly Obertrumia aurea. Paramecium have extrusomes called trichocysts which are released when they encounter predators or when the cell is damaged (see below).  

aramecium caudatum by DIC microscopy. 200X by Robert Berdan ©

Paramecium caudatum by DIC microscopy. 200X

Paramecium showing rows of Trichocyts just under the membrane by Robert Berdan ©

Trichocysts visible below the paramecium's pellicle. 400X DIC microscopy.

Trichocysts from Paramecium DIC microscopy by Robert Berdan ©

Trichocysts released from a Paramecium 400X DIC microscopy

Exploded Nassulid doesn't show any evidence of Trichocyts 100X DIC microscopy by Robert Berdan ©

Exploded nassulid sp doesn't show any evidence of trichocysts 100X DIC microscopy.

Nassulid Extruded cytoplasm 100X DIC microscopy by Robert Berdan ©

Extruded cytoplasm of a nassulid 100X DIC microscopy.

Close up of a Nassulid species showing the Nucleus, above the clear area is part of the contractile vacuole system 200X DIC microscopy  by Robert Berdan ©

Close up of a nassulid species showing the nucleus, and above it the clear area is part of the contractile vacuole system 200X DIC microscopy.

Nassulids (e.g. Nassula ornata) also have a hypoostomial frange (synhymenium) which is composed of a double row of polykinetids (kinetids are basal bodies that form the cilia) running from the left side of the cell to the oral aperture and form a thin row. They can be seen when using a differential interference contrast microscope (DIC) or by silver staining. I found them difficult to see at times, but they can be seen in the movie (3 min 26 seconds) if you pause the movie. Clearer pictures of the hypoostomial frange are shown on M. Plewka’s web site ( 2018).

Exploded Nassulid showing the centrally located contractile vacuole, by Robert Berdan ©

Exploded nassulid showing the centrally located contractile vacuole, extruded nucleus (N) but no extrusomes (trichocysts). 100X DIC microscopy.

Exploded Nassulid showing the cyrtos and Nucleus - no trichocysts (extrusomes) are visible. 200X DIC by Robert Berdan ©

Exploded nassulid showing the (C) cyrtos (nasse) and (N) nucleus - no trichocysts (extrusomes) are visible. 200X DIC.

Nucleus and Crytos (Nasse) in the cytoplasm of an exploded Nassulid ciliate. 630X DIC microscopy by Robert Berdan ©

Nucleus and crytos (nasse) in the cytoplasm of an exploded nassulid ciliate. 630X DIC microscopy.

     The identifying characteristics of the nassulids are a nasse, also called a basket, cyrtos, or cytopharyngeal basket. This structure is easily observed by light microscopy and is shown in some of the photomicrographs here.  These colourful ciliates are fascinating to watch with a microscope and I hope these pictures will inspire others to look for them. Also I suggest viewing some of the YouTube movies below - ideal for couch microscopists. The size of the ciliates I observed varies from about 150 to 300 microns but size and shape can vary considerably in some ciliate species.

closeup of a Nassulid showing a side view of the Nasse  by Robert Berdan  ©

Above closeup of a nassulid showing a side view of the nasse - the arrow points to what appears to be ring near the top of the nasse. 400X DIC microscopy.

I have also photographed other ciliates in the same pond that also have coloured vacuoles - one is shown below - it identity is unknown and it is smaller than then the ones with a nasse.

Unknown ciliate with red granules by Robert Berdan ©

Ciliate with red granules (possibly Holophyra sp). Red algae (Haematococcus pluvialis) are found in some ponds and bird baths and if injested could form red vacuoles. 400X DIC microscopy.

     I have photographed other ciliates with large colourful granules without a nasse (see above). Many ciliates I have photographed have green symbiotic algae inside e.g. Paramecium bursaria, Stentor polymorphus and even Hydra (Hydra viridissma). Some ciliates also produce coloured pigments, Blepharisma is one genus where many species are bright pink in colour (Wikipedia - Blepharisma also see below).

Blepharisma americanum which is pink in colour with 4 macronuclei. Below it is a common ciliate Paramecium caudatum by Robert Berdan ©At the top of the picture is the ciliate Blepharisma americanum which is pink in colour with 4 macronuclei. Below it is a common ciliate Paramecium caudatum.

unknown ciliate with yellow to gold coloured granules by Robert Berdan ©

Ciliate (possibly Holophyra sp) with yellow to gold coloured granules. 400X DIC microscopy.

majority of ciliates appear colourless with some brown or green food vacuoles by Robert Berdan ©

The majority of ciliates I have observed appear colourless with some brown or green food vacuoles.

Theciliates shown in this article were collected from small roadside ponds in the Bearspaw area north of Calgary. Residents in the area probably wonder what I am doing collecting their pond water on Saturday mornings. I usually tell the curious I am doing biodiversity studies of the ponds - which I am! The area is about 10-15 minute drive from our home. The homes in the Bearspaw area are beautiful and many have large acreages of land and ponds - I would love to own my own pond.

Google map of poinds in the Bearspaw region in North Calgary, AB

Google map showing ponds in the Bearspaw part of Calgary NW where my wife and I have collected pond samples from April 30 to the end of October, 2021 (red triangles). Some of the ponds dry up over the summer and deer and moose are common around the small ponds.

To appreciate Nassulids all you need is a light microscope, a few jars and time to collect them. The number and variety of organisms changes throughout the season. I hope to collect samples from under the ice. The good news is that the examination of pond organisms can be done in the comfort of your home using any microscope costing $100 or more (see my article tips for buying a microscope).

Acknowldegements: I thank Bruce Taylor for suggestions and discussions about the ciliates identities in this article. Please visit his web site: and see his videos below. Also I thank my wife Donna for assisting me in collecting pond animalcules - collecting is more fun when you go with someone.

I provide microscope instruction, sell some used microscopes and all my pictures are available for sale for personal or commecial use. The low res images on this web page are free for educational or personal use. Comments and questions are welcome.

References & Websites

S.J. Gershman,  P. EM Balbi, C.R., Gallistel and J. Gunawardena (2021) Reconsidering the evidence for learning in Single Cells. eLife 10: 1-15.

(2021) Nassula – Wikipedia

Ehrenberg (1838) Shows initial paintings of Nassula species

H.M. Carter, S.I. Heaney, J.W.G Lund. (1990) The Ecological significance of grazing planktonic populations of cyanobacteria by the Ciliate Nassula. New Phytol. 114:247-263.

D.H. Lynn (2008) The Ciliated Protozoa. Characterization, Classification and Guide to the literature. Spring Verlag. pg 232-267.

A.Brabrand, B.A. Faafeng, T. Kallqvist, J. P. Nilssen (1983) Biological control of undesirable cyanobacteria in culturally eutrophic lakes. Oecolgica: 60:1-5.

J.B Tucker (1978). Endocytosis and streaming of highly gelated cytoplasm along side of rows of arm-bearing microtubules in the Ciliate Nassula. J. Cell Science 29: 213-232.

J.B Tucker (1968) Fine Structure and Function of the Cytopharyngeal Basket in the Ciliate Nassula. J. Cell. Sci 3: 493 -514.

J.B Tucker (1967) Changes in Nuclear Structure During Binary Fission in the Ciliate Nassula. J. Cell Sci. 2: 481_498.

Klaus Eisler and C.F. Bardele (1983) The alveolocysts of the Nassulida: Ultrasture and some phylogenetic considerations, Ultrastructure and Phylogeny of Ciliates Protistologica. XIX: 95-102.

W. Foissner (1979) Taxonomical studies on the Cilates of the grossglokner area hohe Tauren, Austria VIII. Family Nassulidae.  Naturk. Jahrb. Stadt Linz. 25: 199-208. (In German – describes five species of Nassula).

W. Foissner (1994) Progress in Taxonomy of Planktonic Freshwater Ciliates. Marine Microbial Food Webs, 8: 9-35. Obertrumia aurea (formerly Nassula aurea) shown in Fig. 14. and Nassula ornata with its trichocysts Fig 15, 16, 17 and 18.

W. Foissner (1987) Miscellane Nomenclatoric Cilitea (Protozoa, Ciliophora) Arch Protistenkd. 133: 219-235.

P. Vdacny and E. Tirjakova (2006) First records of soil ciliates (Protozoa, Ciliophora) from classes, Prostomea, Nassphorea, Spirotrichea, and Colpodea in Slovakia. Biolpgia, Bratislava: 61:509-516.

D. Bernhard, D,  D. Leipe, M. L. Sogin and K. Schlegel (1995) Phylogenetic Relationship of the Nassulid with the phylum Ciliophora inferred from the Complete small subunit rRNA gene sequences of Furgasonia bloachmanni, Obertrumia georgiana and Psedomicrothorax  dubius. J. Euk. Microbiol. 42: 126_131.

C.D. Beers (1966) The excystment process in the Ciliate Nassula ornata Ehrbg. J. Protozool. 13:79-83.

Dr. Wilhelm Foissner - 60 years: biographical sketch and bibliography - studied ciliates for most of his life and has left hundreds of publications on them.

G. Deroux (1978) The Hypostome ciliate order Synhymeniida: From Chilodontopsis of Blochman to Nassuloopsis of Faure-Fremiet. Trans. Amer. Soc., 97: 458-469.

M. Plewka (2008-2009) - Nassula pictures - shows hypostomial ciliary band (frange)


Nassula aurea Ehrenberg 1883


Nassula aurea Nassophorea: Nassulida: Nassulinea: Nassulidae

K. Eisler and F. Bardele (1986) Cortical morphology and Morphogenesis of the Nassulid Ciliates Furgasonia blockmanni Faure-Frmiet, 1967 and Nassula Citrea Kahl (1930) Protistologica (1986) 22: 461-476. of_the_nassulid_ciliates_Furgasonia_blochmanni_Faure-Fremiet_1967_and_Nassula_citrea_Kahl_1930


Movies of Nassulids on YouTube

Obertrumia aurea by Bruce Taylor

Obertrumia feeding on Oscillatoria by Bruce Taylor

Nassula ornata by Bruce Taylor

Nassula with conspicuous trichocysts

Nassula: a colourful ciliate and cytopharyngeal basket

Nassula by Don Woodman

Nassula dying – being crushed by coverslip – Couch Microscopy

Nassula dividing – Microgrammer

Nassula and bacteria - Michal Jelenčiak

Microscopic World Nassula sp by Michal Jelenčiak

Nassula sp by MicroWiz

Nassula ornata by Michel-Marie Solito de Solis

Nassula a colourful ciliate  Natural Science


Top of Page

Authors Biography & Contact Information

Portrait of Dr. Robert C. Berdan by Sharif Galal ©

Bio: Robert Berdan is a professional nature photographer living in Calgary, AB specializing in nature, wildlife and science photography. Robert retired from Cell\Neurobiology research to pursue photography full time many years ago. Robert offers photo guiding and private instruction in all aspects of nature photography, Adobe Photoshop training, photomicrography and macro-photography. Portrait of Robert by Dr. Sharif Galal showing some examples of Robert's science research in the background.

Email at: 
Web sites: 
Phone: MST 9 am -7 pm (403) 247-2457.