Zooplankton of the Great Lakes

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Organism: Ploesoma



Kingdom - Animalia

Phylum - Rotifera

Class - Monogonota

Order - Ploima

Family - Synchaetidae

Genus - Ploesoma







Ploesoma is of oval shape with a semi-stiff lorica, that is curved posteriorly. From the lateral view it mimics the shape of a plank, with a view of it’s supported dorsal ridge. (Figure 1.2 & 1.4) It is most distinguishable by the large foot that ventrally protrudes from its midline. (Figure 1.2 - 1.4) (Dang et al., 2013) This foot is flexible, and has two large toes of equal size. Ploesoma’s rami then curve dorsally and display a median row of small teeth and a large set of alulae. (Dang et al., 2013) The large foot is used primarily from swimming and navigation. Figure 6 exhibits the 4 different species of Ploesoma and their distinguishing characteristics.




Figure 1: Ploesoma hudsoni

1.1-4) habitus

1.1) dorsal

1.2 & 1.3) lateral

1.4) ventral, head contracted

1.5) manubrium

1.6) fulcrum



Life History, Reproduction/Growth


Rotifers reproduce via parthenogenesis, unless there is a stressor in the environment such as photo period or a decline in food availability. (Figure 2) Figure 3 demonstrates the effect of temperature on two species of Ploesoma, Ploesoma truncatum and Ploesoma hundsoni. In the 1950’s it was theorized that the D cell in Ploesoma propagates the entire reproductive system. It was suggested that the digestion tract is formed from abstruse cells derived from the lower edge of the germ ring. (De Beauchamp 1956) During gastrulation holoblastic cleavage is present, it is unequal in distribution and somewhat spiral in shape. (Pray, 1965) The ovum of Ploesoma is isolecithally divided and Ploesoma utilizes a vitellarium, a yolk glad that supplies yolk to the developing embryos. (Pray 1965 and Dang 2013) Each embryo is encased in a rigid cuticle which forms an ellipsoid in which the body resides in. (Dang 2013)






Figure 2: Reproduction cycle of rotifers



Figure 3: Average rates of development per day of rotifer eggs in relation to temperature.

Line 5) Ploesoma truncatum

Line 6) Ploesoma hundsoni




Most species of Ploesoma are omnivorous, feeding mostly on other rotifers and Chlamydomonas. One species of Ploesoma, Ploesoma hundsoni, is raptorial. (Figure 1) Ploesoma hundsoni feeds primarily on Cerium, consuming it whole. (Bogaert and Dumont, 1989)



Distribution and Habitat


Ploesoma is a planktonic rotifer that inhabits oligotrophic open waters of large lakes. (Bogaert et al., 1989 and Scruton et al., 1991) The genus Ploesoma is fairly common, but they do not dominant the waterways they colonize. (Scruton et al., 1991) A recent publishing in 2013 founded a new species within the waterways of central Vietnam; Ploesoma asiaticum. (Figures 4 & 5) (Dang et al., 2013)


Ploeseoma resides mostly in the pelagic to semi-pelagic zones of warm summer ponds and lakes. They can tolerate and are most abundant when elevation and pH level are low (7.2.) (Scruton et al., 1991)




Figure 4: Ploesoma asiaticum

4.1-4)          habitus

4.1 & 4.4)    lateral

4.2 and 4.3) dorsal view, head contracted

4.5)             manubrium

4.6)            uncus

4.7)            fulcrum




Figure 5: Ploesoma asiaticum

Trophi scanning electron microscopy

5.1)  dorsal

5.2)  fulcrum, rami, and manubrium

5.3)  rami and uncus

5.4)  rami teeth

5.5)  manubrium

5.6)  fulcrum





Description: 4 species of Ploessoma


Figure 6: 4 Different species of Ploesoma

a)    Ploesoma hudsoni, ventral view

b)   Ploesoma lenticulare, dorsal view of loricae

c)     Ploesoma triacanthum, doral view of loricae

d)    Ploesoma truncatum, dorsal view of loricae

e)    Ploesoma lenticulare, lateral view


Works Cited:


Beauchamp, P. D. (1956). Le développement de Ploesoma hudsoni (Imhof) et l’origine des feuillets chez les Rotiferes. Bull. Soc. zool. Fr, 81, 374-383.


Bogaert, G., Dumont, H.J. (1989). Community structure and coexistence of the rotifers of an artificial crater lake. Hydrobiologia, 167-179.


Dang, M. T., Segers, H., Sanoamuang, L. (2013). Rotifers from Thuy Tien lake and Nhu Y river in central Vietnam, with a description of Ploesoma asiaticum new species (Rotifera: Monogononta). Journal of Limnology, 72(2), 376-386.


Edmondson, W. T. (1959). Freshwater Biology (2nd ed.). USA: John Wiley & Sons.


Pray, F.A. (1965, April). Studies on the Early Development of the Rotifer Monostyla cornet Müller. Transactions of the American Microscopical Society, 84(2), 210-216.


Scruton, D.A., Chengalath, R., Carter, J. C. H., Taylor, W.D. (1991, October). Distribution of Planktonic Rotifers and Crustaceans in One Hundred and Eight Lakes from Insular Newfoundland. Canadian Technical Report of Fisheries and Aquatic Sciences, 1825.