Metopus convexus (Kahl, 1927)

Most likely ID: n.a.


Synonym: n. a.


Sampling location: Purren pond, Simmelried


Phylogenetic tree: Metopus convexus



  • body twisted, apical dome to the left, anterior end to the right
  • curved or almost U-shaped in ventral or dorsal view
  • length about 45 µm
  • adoral zone short, mouth opening in mid-body
  • perizonal ciliary row running parallel to adoral zone
  • macronucleus oval located in apical dome
  • contractile vacuole terminal
  • tuft of some elongated caudal cilia
Metopus convexus

The only description and drawing of Metopus convexus known to me is by Kahl and is very short. In my sites Simmelried and Purren pond I find Metopus convexus rarely, but regularly. Although the species is smaller than 50 µm, it can be recognized by the typical curved body shape even at low and medium magnification. Some specimens are almost U-shaped. Thereby the two legs of the U (i.e. anterior and posterior end) are also twisted against each other. That means the body is curved and twisted. Examination of Metopus convexus is not easy, because in my experience the species is quite coverslip sensitive and denatures quickly when the layer thickness is reduced.


The apical dome of Metopus convexus is prominent and strongly protruded. In my population the macronucleus was localized in the anterior half near the apical dome (s. fig. 3c). I have not been able to clearly identify the micronucleus. Kahl does not mention it either. According to my observation, the adoral zone begins at the right side of the dome and extends to the left to mid-body, where the mouth opening is localized. Above the adoral zone the perizonal ciliary row runs parallel also to the mouth opening (s. fig. 3a). At the posterior end, some elongated caudal cilia protrude in a fan shape (s. figs. 1d, 2b and 3c). The contractile vacuole lies terminal. In the cytoplasm I could clearly recognize symbiotic bacteria (s. fig. 3c). Kahl does not mention them, but many other metopid ciliates have also  symbiotic bacteria.


Fig. 1 a-d: Metopus convexus. L = 49 µm. A freely swimmíng specimen from dorsal (a, b), left (c) and ventral (d). Obj. 60 X.


Fig. 2 a-c: Metopus convexus. L = 44 µm. A freely swimmíng specimen from dorsal (a, b) and from the right side (c). Obj. 100 X


Fig. 3 a-c: Metopus convexus. L = 46 µm. Ventral view of slightly squashed specimen. Note the row of perizonal cilia (PC) running parallel to the adoral zone of membranelles (AZM) to the mouth opening in mid-body. CC = caudal cilia,  CV = contractile vacuole, Ma = macronucleus, SB = symbiotic bacteria in the cytoplasm. Obj. 100 X