shanesmicroscope's Identifications

Chaetonotus (Zonochaeta) succinctus VOIGT, 1902 belonging to the subgenus Zonochaeta, from the northernmost edge benthos of freshwater glacial kettle hole Kellis Pond. Imaged in Nomarski DIC on Olympus BH2S using SPlan 40 0.70 objective and SPlan 100 1.25 oil immersion objective plus variable phone camera cropping on Smasung Galaxy S24. The animal measures 200 um in length.

Thanks to Michael Müller who identifies this. He wrote:
This is definitely Chaetonotus (Zonochaeta) succinctus VOIGT, 1902:

a pair of long bristles at the base of the toes, extending beyond the adhesive tubes
a pair of lateral long bristles somewhat in front of the toes
9 long bristles in a line in the middle of the trunk
bigger round scales behind the girdle of the long bristles, smaller scales in front of them
ventral:
no terminal plates
terminally many (18-20) rows of very small oval keeled scales
in the pharynx region rectangular braces
ciliated bands split in several branches near the mouth
pharynx with a strong terminal bulbus
length of 200µm fits perfectly (190µm - 235µm)
Ch. succinctus is a typical member of the muddy benthos. Not very rare, but I doubt, that there are many people around, who have already seen it!

Dr. Martin Kreutz has shown this species on his website: https://realmicrolife.com/chaetonotus-succinctus/

*body vigorous, stocky
*length 190–235 µm
*head weakly five-lobed, 4 lateral tufts of cilia,
*cephalion present
*two pairs of dorsal setolae at posterior end on large special scales
*toes 32–39 µm long with short base and thin adhesive tubes
*girdle of 9 curved, simple spines near mid-body on dorsal side
*11 dorsal longitudinal rows of polygonal scales with small keels in anterior half
*7 dorsal longitudinal rows of large bilobed keel scales, which medially carry a spiny tip and overlap strongly in posterior half
*laterally on posterior trunk 2 long spines
*on base of furca 2 long spines exceeding the length of toes
*ventral ciliated bands split anteriorly into several branches
*ventral side with 18–20 longitudinal rows of minute oval keel scales
*without terminal plates on ventral side

"Chaetonotus succinctus is very distinctive, due to its row of 9 long spines in the middle of the body and two further pairs of long spines in the posterior half of the body. It can be confused with Chaetonotus aemilianus and Lepidochaetus zelinkai, which also have a girdle of spines in the middle of the body. However, the spines of these species have secondary spines, whereas in Chaetonotus succinctus they are simple. Another characteristic feature of Chaetonotus succinctus is the alternation of the scale form above and below the girdle of long spines. The posterior half is covered with larger scales" (1).

1. https://realmicrolife.com/chaetonotus-succinctus/