Zooplankton of the Great Lakes

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Organism: Trichocerca sp.

Figure 1 : Drawing of Trichocerca sp. that does not have anterior mucrones (spines). Cilia coming out the anterior end are labeled as well as the toes and foot.

Drawing taken from Jennings (1900).



Phylum: Rotifera

Class: Monogonta

Order: Ploimida

Family: Trichocercidae

Genus: Trichocerca


This classification is the most current, however in older texts, such as Jennings (1900, 1903), the family may be listed as Rattulidae. Different species of the now Trichocerca may also be listed as Rattulus and Mastigocerca. A nice break down of species synonyms can be found in Harring (1913).



The genus Trichocerca are loricate rotifers with a foot and one or two toes present. The toes can be equal length (Figures 5 and 6), or can be substantially different(Figures 1-4). In many cases where the toes are of unequal length, the short toe is often twisted around the long toe (Figures 2 and 3 ). On the anterior end of Trichocerca, mucrones (spines) can also be present (Figures 5 and 6). In some species, the lorica of the animal can also be straited (Jennings 1900). Some Trichocerca also have well developed mucus glands that they can use to attach themselves to different substrates, such as plants and rocks.

Figure 2 : Empty lorica of Trichocerca sp. that does not have anterior mucrones. This species has one long toe and one toe that is much smaller and curved, seen more clearly in the enlarged image.


Figure 3: Close up of small, curled toe.


To determine an animal to the species level, dissecting out the trophi(jaw) is often necessary (Chengalath and Mulamoottil 1975). This can accomplished by soaking the animal with sodium hypochlorite to eat away the soft parts, leaving the sturdy trophi (Figure 7). The trophi of Trichocerca are generally unsymmetrical, with the right manubrium smaller, and sometimes very rudimentary (Jennings 1900).



Trichocerca is found throughout the world (Seger 2003). In the analysis, 67 taxa were studied, and 26 of them showed no latitudinal preference. Interestingly though, there is a high rate of endemisim found only in the Northern Hemisphere, with taxa in Southern Hemisphere being more cosmopolitan. Specific to North America, there are 9 endemic species, which seem to be confined to the Great Lakes and Northeast regions. Based on this and other evidence, the origin of Trichocerca seems to be of Laurentian origin (Seger 2003).



Figure 4: Same species of Trichocerca as in Figure 2 , but with guts still present.

Figure 5: Drawing of Trichocerca sp. That has anterior mucrones. This species has two toes that are similar lengths.

Drawing from Pennak (1978).

Habitat and Feeding Ecology

Trichocerca are most commonly found in the periphyton(attached to things), but can also be planktonic (Pejler and Bērziņ 1993). They have been found in lakes, pools, running water localities and mires (bogs). Where they are found is associated with their food source. Three species described in this paper are predators on rotifer eggs, and are most commonly found in the pelagic region. Most species however are grazers, and eat algae and other small particles in the water column. These species tend to live semi-planktonic between the substrate they are attached to and open water.


Figure 6 : Trichocerca sp. with anterior spines present. Foot and toes are also labeled. In this species, the two toes are of very similar length, unlike the species shown in Figures 1-4.



Figure 7. Examples of various Trichocerca tropi (jaws). Drawing taken from Chengalath and Mulamoottil 1975.


Life history, reproduction and growth

As a member of the phylum Rotifera, Trichocerca are eutelic, or they born with a set number of cells. As the rotifer grows, these cells expand and elongate, but do not divide. Rotifers can grow from egg to adult in as few as 1-2 days. The rotifer lifecycle has a major parthenogenetic component; female rotifers asexually produce a diploid egg that is a clone of themselves. This develops inside the lorica until it is ready (Figure 8). They continue to reproduce in this way until a stimulus is present, and then females will produce haploid eggs, which if left unfertilized will develop into males. The haploid males will produce sperm that then fertilizer other haploid eggs, producing a new diploid generation.


Figure 8 : Trichocerca sp. with large egg present inside lorica.

Works Cited:

Chengalath, R., and Mulamoottil, G. 1975. Littoral Rotifera of Ontario- genus Trichocerca Canadian Journal of Zoology 53:1403-1411.

Harring, H.K. 1913. Synopsis of the Rotatoria. Bulletin of the United States National Museum 81:1-226.

Jennings, H. S. 1900. Rotatoria of the United States: With Especial Reference to Those of the Great Lakes. Bulletin of the United States Fish Commission 19:67-104.

Jennings, H.S. 1903. Rotatoria of the United States. II A monograph of the Rattulidae. Bulletin of the United States Fish Commission 22: 273-352.

Pejler , B. and Bērziņ, B. 1993. On the ecology of Trichocercidae(Rotifera). Hydrobiologia 263:55-59.

Pennak, R.W. 1978. Fresh-water invertebrates of the United States. pg. 190. John Wiley and Sons, Inc.

Seger, H. 2003. A biogeographical analysis of rotifers of the genus Trichocerca Lamarck 1801 (Trichocercidae, Monogononta, Rotifera), with notes on taxonomy. Hydrobiologia 500:103-114.