Ditrema mikrous (de Saedeleer, 1934)
Most likely ID: n.a.
Synonym: n. a.
Sampling location: Simmelried
Phylogenetic tree: n.a.
- shell hyaline, thin, without xenosomes, sometimes covered with brownish crust
- in frontal view spherical or oval, sometimes irregular or angular
- in lateral view dome-shaped
- shell with two opposite necks
- length of shell (inclusive necks) 9.3–13.6 µm
- diameter of necks 1.7–2 µm
- protoplast fills shell not completely
- granofilopodia form a dichotomously branched and anastomizing network
- nucleus central, with a single nucleolus
- several contractile vacuoles
So far I could detect Ditrema mikrous only in the Simmelried. Like the similar species Ditrema longicollis, Ditrema mikrous likes to settle on floating coverslips. I could observe both species in parallel on the same coverslips. The main distinguishing feature from Ditrema longicollis is the size. According to De Saedeleer, 1934 (s. literature) Ditrema mikrous with 9, 3 – 13,6 µm length (including the necks) is only half the size of Ditrema longicollis. I can confirm these size differences. In my population the length of the specimens was 12,3 – 13,9 µm which agrees well with the data of De Saedeleer. I could also observe that the shells of some specimens were covered with a brownish crust (s. fig. 3). This was different from the orange-brown or brown discoloration caused by iron deposits that occur in Ditrema longicollis. Since I did not find any Ditrema shells with a length of 14–23 µm (i.e., the gap between the size specification of Ditrema mikrous and Ditrema longicollis), Ditrema mikrous cannot be a smaller variant of Ditrema longicollis, confirming De Saedeleer’s delimitation.
More images and information of Ditrema mikrous: Ferry Siemensma-Microworld-Ditrema mikrous
Fig. 1: Ditrema mikrous. L = 13.9 µm (inclusive necks). A partly extended specimen with an irregularly shaped shell. Obj. 100 X.
Fig. 2: Ditrema mikrous. L = 12.2 µm (inclusive necks). A partly extended specimen with a spherical, hyaline shell. Obj. 100 X.
Fig. 3: Ditrema mikrous. L = 12.4 µm (inclusive necks). A fully extended specimen with a broad oval shell covered with a brownish crust. Obj. 100 X.