Metopus laminarius (Kahl, 1927)
Most likely ID: n.a.
Synonym: n. a.
Phylogenetic tree: Metopus laminarius
- body cylindrical, sometimes irregular due to food content
- posterior end transversely truncated
- length 200–260 µm
- always with pink rhodobacteria in food vacuoles
- cytoplasm sometimes yellowish
- anterior end flattened and spirally elongated
- adoral zone runs along the spiral extension to mouth opening
- mouth opening in anterior third
- contractile vacuole terminal, often dilated toward anterior end
- macronucleus sausage-shaped in anterior end, often curved into a horseshoe shape
- micronucleus spherical, adjacent to the macronucleus or enclosed by it in a U-shape
- very fine, long caudal cilia (hard to see)
In my sampling sites Purren pond and Simmelried I find Metopus laminarius frequently and regularly. It is one of the largest species of the genus Metopus. Kahl gives a range of 200–260 µm for the body length and distinguishes a variety “minor” (s. right drawing above) with a length of about 150 µm. In my population I could find specimens with lengths between 170 – 320 µm. The body size seemed to depend strongly on the number of food vacuoles in the body. Well fed specimens were larger. Therefore, in my opinion, the variety “minor” is not justified, since it is only a sign of nutritional status. As described by Kahl, the food vacuoles of Metopus laminarius are mainly filled with pink rhodobacteria (s. fig. 2b). The cytoplasm often appeared faintly yellowish. The anterior end is flattened and twisted in a clockwise running spiral. The adoral zone follows this spiral and sinks ventrally into the mouth opening (s. fig. 3a). The long caudal cilia, described and drawed by Kahl, are hard to see. Only in one specimen I could document them (s. figs. 2 a and 2 c). In other specimens I sometimes could not see them at all. Possibly they are shed off quickly. Metopus laminarius lacks a fringe of extrusomes under the pellicle, but it appears finely granulated (s. fig. 5).
Fig. 1 a-c: Metopus laminarius. L = 312 µm. A freely swimming specimen from ventral (a, b) and from left (c). Note the spirally twisted anterior end. Ma = macronucleus. Obj. 40 X.
Fig. 2 a-c: Metopus laminarius. L = 180 µm. A freely swimming specimen from ventral. Note the long caudal cilia (CC). RB = food vacuoles filled with ingested rhodobacteria. Obj. 60 X.
Fig. 3 a-b: Metopus laminarius. L = 280 µm. The slightly squashed specimen from ventral (a) and from right (b). AZM = adoral zone of membranelles, Ma = macronucleus, Mi = micronucleus. Obj. 60 X.
Fig. 4 a-b: Metopus laminarius. A specimen with a horseshoe shaped macronucleus (Ma) during continuous reduction of the layer thickness. The macronuclus encoleses the spherical micronucleus (Mi). Obj. 60 X.
Fig. 5: Metopus laminarius. Focal plane on the granulated pellicle in a squashed specimen. Obj. 60 X.