Cinetochilum margaritaceum
(Ehrenberg, 1831) Perty, 1849
Most likely ID: n.a.
Synonym: – –
Sampling location: Simmelried, Purren pond
Phylogenetic tree: Cinetochilum margaritaceum
Diagnosis:
- length 20 – 40 µm
- discoid ciliate, flattened dorso-ventrally
- apical end rounded
- posterior end slightly truncate
- oral apparatus located at posterior end, left side
- extrusomes 3 µm long
- contractile vacuole sub-terminal
- globular macronucleus positioned centrally with one adjacent micronucleus
- several caudal cilia (4-5)
Cinetochilum margaritaceum is one of the most common ciliates besides Cyclidium, Paramecium or Coleps. Although it is so common and can occur in masses, it is not a particularly easy target for photography because it is only 15 – 40 µm in size, usually staying below 30 µm. Therefore, there are not as many light microscopic examinations as one would think. Under the coverslip, Cinetochilum is not a fast swimmer and likes to gather around particles of detritus, where the ciliate grazes on bacteria. Here a freely moving specimen with the 60 X objective:
Fig. 1 a-d: Cinetochilum margaritaceum. L = 24 µm, ventral view of a freely swimming specimen. CC = caudal cilium, Obj. 60 X.
The ventral side of Cinetochilum margaritaceum is finely furrowed. The furrows originate apically and run across the cell body in counterclockwise fashion. The oral apparatus is located posteriorly at the right side. The oral opening is almost rectangular in optical section. The right side of the mouth opening is encompassed by the undulating membrane (UM). The contractile vacuole (CV) is located to the left of the oral apparatus at the posterior end. In my population of Cinetochilum margaritaceum the macronucleus (Ma) was not located centrally but in the posterior third of the cell:
Fig. 2 a-d: Cinetochilum margaritaceum. L = 25 µm, slightly pressed specimen, ventral view, focus on oral apparatus. EX = extrusomes, Ma = macronucleus, Mi = micronucleus, OA = oral apparatus, UM = undulating membrane, Obj. 100 X.
The dorsal side is wider and more deeply furrowed. The furrows run clockwise. Between the furrows 2-3 µm long extrusomes (EX) are intercalated. The furrows run to the posterior end where they form a notched posterior margin. From these notches caudalcilia (CC) arise which are about 15-20 µm long. According to my observations there are 4 in every cell. Literature sources indicate a range of 3-5:
Fig. 3 a-c: Cinetochilum margaritaceum. L = 25 µm, slightly pressed specimen, dorsal view. CC = caudal cilium, CV = contractile vacuole, DF = dorsal furrows. Obj. 100 X.
Fig. 4: Cinetochilum margaritaceum. Ventral view, the oval shape of the cell has characteristic indentation at the posterior right margin (arrow). Obj. 100 X.
Fig. 5: Cinetochilum margaritaceum. a) Dorsal view of the rows of extrusomes arranged between the dorsal furrows. EX = extrusomes. Obj. 100 X. b) Ventral view of a squashed specimen. Ma = macronucleus, UM = undulating membrane. Obj. 100 X.
The oval body of Cinetochilum margaritaceum is distinctly flattened dorso-laterally, which is very well seen in a lateral view (s. Fig. 6a). The right picture (s. Fig. 6b) shows an optical section through the posterior end demonstrating the position of the mouth opening and the contractile vacuole (CV):
Fig. 6 a-b: Cinetochilum margaritaceum. a) Lateral view. CV = contractile vacuole, OA = oral apparatus. Obj. 100 X. b) Posterior view. AM = adoral membranelles, CV = contractile vacuole. Obj. 100 X.
Kahl also describes a form of Cinetochilum margaritaceum with symbiotic algae. I found this form rarely but regularly in Simmelried as well as in the Purren pond. The green form of Cinetochilum margaritaceum contains 15 -20 symbiotic algae (Ø = 6 µm) and is somewhat larger with a distinctly different behavior compared to the colorless form. While the colorless form moves in small circles, the green form swims around quite fast and hardly ever rests. In addition it is sensitive to pressure of the coverslip. So images can only be obtained with more effort. Considering the differences to the colorless form (size, symbiotic algae and behavior) I think we can safely assume the two morphotypes to be in fact separate species:
Fig. 7: Cinetochilum margaritaceum, green form. L = 34 µm, ventral view. EX = extrusomes, OA = oral apparatus. Obj. 100 X.
Fig. 8: Cinetochilum margaritaceum, green form. L = 34 µm, lateral view. Obj. 100 X.
Fig. 9: Cinetochilum margaritaceum, green form. L = 34 µm, dorsal view with focus on the symbiotic algae SA (left) and the caudal cilia (right). OA = oral apparatus. Obj. 100 X.