Chaetonotus acanthodes (Stokes, 1887)
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Simmelried
Phylogenetic tree: Chaetonotus acanthodes
Diagnosis:
- body very stout, stumpy form, shoe-shaped
- head weakly five-lobed
- length 125–145 µm
- hypostomium developed as rectangular plate
- dosal scales keeled with simples spines, oval to circular with an upturned margin
- dorsal girdle of 7–11 straight spines below mid-body, spines 10–25 µm long
- dorsal scales behind the girdle region are unspined
- ventral interciliary field with round or oval scales with a short spine
- ventrally at posterior end 4 elongated terminal scales with spines
- each two large spines located laterally at the posterior end
So far I have found only one specimen of Chaetonotus acanthodes in the Simmelried, but I cannot exclude that I missed this species earlier. The dorsal scales were still drawn with a distal incision by Stokes, but this turned out to be incorrect. A redescription of Chaetonotus acanthodes was made by Kånneby (2013) based on 12 investigated specimens. He recognized the round shape of the scales, as I also observed (s. fig. 2 b). Characteristic features of Chaetonotus acanthodes are also that the girdle of elongated spines is below the middle of the body and that these spines are not arranged on a line. Above this girdle the dorsal scales bear short spines and below it they do not (s. fig. 2 a-b). Below the girdle, there are also two scales with a double keel (s. fig. 3). The scales on the ventral side are small, round and bear short spines (s. fig. 4). At the posterior end four elongated terminal scales with spines are located arranged parallel to each other (s. fig. 5).
Fig. 1 a-d: Chaetonotus acanthodes. L = 140 µm. Different focal planes from dorsal of a freely swimming specimen. Obj. 40 X.
Fig. 2 a-b: Chaetonotus acanthodes. L = 140 µm. Two focal planes from dorsal of a squashed specimen. Note that the dorsal scales below the girdle of spines do not bear spines, but are merely keeled. GS = girdle of spines, PS = posterior spines. Obj. 100 X.
Fig. 3: Chaetonotus acanthodes. The dorsal scales in the region of the girdle of spines in detail. Note the double-keeled scales (DKS) near the posterior end. Obj. 100 X.
Fig. 4: Chaetonotus acanthodes. Focal plane on the interciliary field of the ventral side with small, circular scales and the elongated terminal scales (TS) at the posterior end. Obj. 100 X.
Fig. 5: Chaetonotus acanthodes. The four terminal scales (1–4) at the posterior end on the ventral side in detail. Obj. 100 X.