Chaetonotus oculatus (Schwank, 1990)
Most likely ID: n.a.
Sampling location: Simmelried
Phylogenetic tree: Chaetonotus oculatus
- body shoe-shaped
- length 90–130 µm
- head strongly five-lobed with 4 tufts of long cilia
- two ocelli present
- pharynx cylindrically shaped
- toes 11–15 µm long, completely covered with keeled scales
- tubes reaching half of toes length
- dorsally 11 longitudinal rows of scales
- keeled scales escutcheon-shaped with a short spine arising at distal end
- distal rim of scales with an indentation
- ventral scales are not described
I have found Chaetonotus oculatus so far exclusively in the Simmelried between decomposing plant masses but also in the uppermost mud layer. So far I have found only one specimen in March 2023. However, I cannot exclude that I missed the species earlier because of its small size.
The species can be identified by a combination of certain characteristics. First, Chaetonotus oculatus is comparatively small. My specimen was 88 µm in length, at the lower limit of the range given by Schwank, 1990 (s. literature). Spherical ocelli are found on both sides of the head (s. fig. 2). The dorsal scales are distinctly keeled and have a short, curved spine at the distal end, but this can only be seen in lateral view (s. fig. 5). The scales are narrow, almost parallel-sided, and the posterior margin is distinctly incised (s. fig. 4). I could not examine the ventral scales (if present) because I had only this one specimen.
Fig. 1 a-d: Chaetonotus oculatus. L = 88 µm. A freely swimming specimen in dorsal view. Obj. 40 X.
Fig. 2: Chaetonotus oculatus. L = 88 µm. A slightly squashed specimen from dorsal. Note the two ocelli (OC) located near the lateral lobes of the head. Obj. 100 X.
Fig. 3 a-b: Chaetonotus oculatus. L = 88 µm. Two focal planes of the dorsal scales. Obj. 100 X.
Fig. 4: Chaetonotus oculatus. The dorsal scales at the posterior end in detail. Note the distal indentations of the scales (arrows). Obj. 100 X.
Fig. 5: Chaetonotus oculatus. The dorsal scales with short spines at the distal end (arrows) in lateral view. Obj. 100 X.