Zooplankton of the Great Lakes

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Testudinella sp.

Taxonomy

Kingdom: Animalia
Subkingdom:
Bilateria
Infrakingdom: Protostomia

Superphylum: Platyzoa
Phylum:
Rotifera Class: Monogonta

Subclass: Monogononta Superorder: Gnesiotrocha

Order: Flosculariaceae Family: Testudinellidae Genus: Testudinella

 

Figure 1: Testudinella sp. Collected from Memorial Pond, 2004.

Full Known Species List

1.ahlstromi

16.epicopta

31.parva

2.amphora

17.gillardi

32.patina

3.andranomenensis

18.greeni

33.reflexa

4.angulata

19.haueriensis

34.robertsonae

5.aspis

20.husseyi

35.sphagnicola

6.berzinsi

21.incisa

36.stappersi

7.brevicaudata

22.kostei

37.striata

8.brycei

23.magna

38.subdiscoidea

9.caeca

24.mucronata

39.triangularis

10.carlini

25.munda

40.tridentata

11.clypeata

26.neboisi

41.truncata

12.dendradena

27.obscura

42.unicornuta

13.discoidea

28.ohlei

43.vanoyei

14.elliptica

29.ovata

44.walkeri

15.emarginula

30.panonica

45.wuhanensis

 

 

46. jhujiangensis

Classification


Testudinella was first characterized by Bory de Saint-Vincent in 1826 (GLERL 2015). It was named for its shell-like, circular lorica. Since then, 45 additional species have been discovered.

 

Anatomy

 

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, Germany, 2014.

 

 

 

 

 

 

Figure 3: Movement of Testudinella incis, Pond Collection from Hattingen Felderbachtal, Germany, 2014.

 

During movement, the lorica of Testudinella curves at the edges, possibly aiding in motility.

 

 

 

 

Figure 4: Ciliated Corona and Eyespots of Testudinella incis, Pond Collection from Hattingen Felderbachtal, Germany, 2014.

 

This image illustrates the exposed head and foot of Testudinella. The ciliated corona and red eyespots are clearly distinguishable.

 

 

 

Trophic Structures

 

 

 

 

Figure 5: Trophi of Testudinella zhujiangensis, Collection from Pearl River Estuary, China, 2007.

 

The flattened trophi of Testudinella illustrate their reliance on plant matter for food. This trophic structure is beneficial in the grinding of plant matter.

 

A.

 

 

Figure 6: SEM Comparison of Different Rotifer Trophi.

 

The trophi labeled A above represents that of Testudinella clypeata. Though slight differences in trophi shape occur between species, the general trophic structure of Testudinella remains differentiable from those of other rotifers.

 

 

 

Differences in Body Shape Between Species

 

 

Figure 7: Testudinella elliptica, Pond Collection from Gevelsberg. Germany, 2006.

 

Testudinella elliptica represents a species of Testudinella which is ovular in shape.

 

Figure 8: Testudinella epicopta.

 

This species of Testudinella exhibits an elongated body and lengthened coronal cilia.

 

 

 

 

 

Figure 9: Testudinella tridentata.

 

Testudinella tidentata exhibits a much more angular and rigid lorica than other species, it also has a significantly longer foot.

 

 

Figure 10: Testudinella patina.

 

Testudinella patina exhibits the typical, circular body shape that the genus has come to be recognized by.

 

 

Distribution

 

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).

Feeding

 

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.

 

https://youtu.be/Za4wIunpKbg

 

https://youtu.be/3DxsFm8ulpM

 

 

Reproduction

 

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).

Works Cited:

Fontaneto, D., Melone, G. and De Smet, W.H. (2008). Identification key to the genera of marine rotifers worldwide. MEIOFAUNA MARINA Biodiversity, morphology and
ecology of small benthic organisms
16, 75-100.

Glime, J. M. (2013). Invertebrates: Rotifer Taxa. (E-Book) Michigan Technological University and the International Association of Bryologists ch. 4-6, 16-
17.

Great Lakes Environmental Research Laboratory. (2015). Sea Grant Great Lakes Network (online). Accessed at https://www.glerl.noaa.gov

Leitner, M. and Jersabek, C. (2016). Rotifer World Catalog (online). Accessed at http://rotifera.hausdernatur.at

Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. (2016). The Animal Diversity Web (online). Accessed at
http://animaldiversity.org.

Plewka, M. (2006), (2014). PlingFactory (online). Accessed at www.plingfactory.de

Wei, N., De Smet, W.H., and Xu, R. L. (2010). A New Species of Testudinella (Rotifera: Testudinellidae) From Qiao Island, Pearl River Estuary, China. Acta
Zoologica Academiae Scientiarum Hungaricae 56 (4)
, 307315
.