Chaetonotus succinctus (Voigt, 1902)
Most likely ID: n.a.
Synonym: n. a.
Sampling location: Purren pond, Simmelried
Phylogenetic tree: Chaetonotus succinctus
Diagnosis:
- 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 (s. figs. 1b and 2). 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 (s. fig. 4). The posterior half is covered with larger scales. I find this species only rarely, so far only in Purren pond and Simmelried, respectively in May and August.
Fig. 1 a-c: Chaetonotus succinctus. L = 207 µm. Lateral view from left (a, b) and dorsal view (c) of a freely swimming specimen. Obj. 40 X.
Fig. 2: Chaetonotus succinctus. L = 207 µm. Lateral view from left with the girdle of long spines in mid-body (GS), the lateral spines (LS) and the posterior spines (PS). Obj. 60 X.
Fig. 3 a-b: Chaetonotus succinctus. L = 220 µm. Two focal planes of a slightly squashed specimen from dorsal. Of the 9 spines of the girdle in mid-body only 8 are visible, because one spine is out of focus. Obj. 60 X.
Fig. 4: Chaetonotus succinctus. L = 220 µm. A strongly squashed specimen from dorsal. Note that both the shape and the number of rows of dorsal scales are different in the anterior and posterior half of the body, separated by the girdle of the 9 long spines. Obj. 100 X.