Zooplankton of the Great Lakes
Site created by: Baihleigh Talon
Subclass: Monogononta Superorder: Gnesiotrocha
Order: Flosculariaceae Family: Testudinellidae Genus: Testudinella
Figure 1: Testudinella sp. Collected from Memorial Pond, 2004.
Full Known Species List
Most Testudinella are characterized by a round, nearly completely circular shaped body. Individuals are capable of retracting both their ciliated head and foot into their loricae. Testudinella have two eye spots and distinctive visible musculature. The lorica is unique in Testudinella in that its ventral and dorsal plates are completely fused laterally (Glime 2013). Species differ in morphology mostly in the shape of the lorica, which varies in oval, vase-like, and circular forms. Some species, however, also differ in the length of their foot, which can be particularly longer or shorter than others.
General Body Plan
Unlike all other types of rotifers, the foot of Testudinella contains cilia at its end. Figure 2: Testudinella incis,
Pond Collection from Hattingen Felderbachtal,
Unlike all other types of rotifers, the foot of Testudinella contains cilia at its end.
Figure 2: Testudinella incis, Pond Collection from Hattingen Felderbachtal, Germany, 2014.
Differences in Body Shape Between Species
Species of Testudinella can be found worldwide. Most inhabit freshwater lakes and ponds, but eleven species have been isolated in salt water environments. Five of these species live exclusively in haline environments, inhabiting marine and brackish waters. The remaining species are haloxenous or euryhaline. Testudinella are known to inhabit the benthic, periphytic, and interstitial areas of the water column (Wei et. al. 2010). Some species are free-swimming in the littoral zone, where sunlight can reach the sediment through the water, and where plant life is abundant. They can also be found in sphagnum pools and among aquatic plants (Glime 2013).
Testudinella patina, illustrated in Figure 10 above, has been located among arctic mosses in the Antarctic ocean (Glime 2013). Interestingly, Testudinella patina can also be found in Lake Erie, of the Great Lakes (GLERL 2015). Like some species, T. patina has a tolerance for a wide array of salt levels in its environment (Wei et al. 2010).
Testudinella feed primarily on algae, bacteria, and debris, using their ciliated corona to pull particles into their mouths (GLERL 2015). Sometimes Testudinella will sit still, waiting for particles to pass by, other times they will actively chase after particles, usually in a spinning movement. The videos below illustrate their feeding processes.
As members of the family Monogonata, most individuals in a population are diploid females, reproducing through parthenogenesis. Under the influence of certain stimuli in the environment (possibly overcrowding, poor water conditions, or food depletion), females will produce females which themselves produce haploid eggs. These become males if unfertilized. If fertilized, however, a diploid, resting egg will be produced. These can remain dormant for some time until conditions become acceptable again. Resting eggs give rise to regular, diploid females. Males are significantly smaller than females, and usually have a much reduced life-span, as their main purpose is reproduction (GLERL 2015).
Fontaneto, D., Melone, G. and De Smet,
W.H. (2008). Identification key to the genera of marine
rotifers worldwide. MEIOFAUNA MARINA Biodiversity,