Chaetonotus oculatus (Schwank, 1990)

Most likely ID: n.a.


Synonym: 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
  • phayrnx 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
Chaetonotus oculatus

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 & Bartsch, 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 imdentations 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.