For the subgenus Hystricochaetonotus are the relatively large, non-overlapping scales with a long spine. This subgenus owes its name to this spiny appearance (hystix = porcupine).
The scales are in typical arrangement. Their shape is trilobate with a central keel, at the end of which arises a long spine - usually with a secondary tip:
typical three-lobed scales in Hystricochaetonotus - here
C. (H. ) persetosus
Dorsal scales: 13 rows of 13-14 three-lobed scales (6.5µm x 5µm) with simple spine (3µm - 10µm); typical scale group for Hystricochaetonotus without spines at the posterior end
Ventral scales: ventral intermediate field with two rows of 20 rectangular scales each (1.2µm - 4µm); two keeled terminal plates (length 6.4µm - 6.8µm)
Oecology: Moor
Similar species: all Hystricochaetonotus; precise diagnosis required
Particularities: Spines without secondary tip; unique scaling of the ventral intermediate field
The small gastrotrich Chaetonotus (H.) italicus, previously only known from Italy, is relatively common in the Sima bog.
Ch. italicus: dorsal
Many of the specimens found were in their post-parthenogenetic (hermaphroditic) phase and bore both a distinct, bipartite X-organ and rod-shaped spermatoids. The pronounced dumbbell-shaped pharynx is typical of the species:
Ch. italicus: t.s.
The ventral intermediate field is covered with two rows of rectangular scale plates, which become more indistinct in the neck area. Two keeled terminal plates form the end:
Ch. italicus: ventral
Although the scale spines do not have a secondary tip, the classification in the subgenus Hystricochaetonotus is clear due to the typical scale shape:
Ventral scales: 2 long, thin terminal plates with short spines; 7-8 rows of small keel scales (1µm - 3µm)
Oecology: Moor, bank moss
Particularities: Toes naked; rigidly protruding spines are very typical
The very rare gastrotrich Chaetonotus (H.) murrayi is only known from two localities (in Poland and near Berlin). The strong and quite long two-pointed spines protrude in a spear shape and give the animal a very defensive appearance.
Ch. murrayi: cross section
This is particularly noticeable when focusing on the spines on the back:
Ch. murrayi: dorsal
The approx. 20µm long spines have a lateral secondary spine near the main spine:
Ch. murrayi: focus on the spine tips
The focus on the scales shows the typical three-lobed scale shape of this subgenus. In contrast to the findings in the literature, the entire head of the animals is also covered with long spines:
Ch. murrayi: dorsal scaling of the head / neck area
The spination is also clearly pronounced at the posterior end. Unlike many members of the subgenus Hystrocochaetonotus this species lacks the unspined dorsal keel plates:
Ch. murrayi: dorsal scaling of the hind end
The ventral intermediate field bears 6 - 7 rows of small keel scales and is terminated by two spiny terminal plates.
Ch. murray: Scales of the ventral intermediate field
Dorsal scales: 7 rows on the head, 12 on the trunk, each with 14-15 three-lobed, keeled scales (3-6 µm), which do not overlap and are short and delicately spined (10 µm); two rows of longer spines at the head end. Very long spines with two secondary tips (26-50 µm) in a relatively narrow field on the anterior trunk
Ventral scales: 2 elongate-oval, keeled terminal plates (6.6µm x 4µm) with two simple spines; 4-6 rows with 40 oval keel scales each. Own observation: in pharyngeal region rectangular transverse claspers
Oecology: Moor, plant-rich small bodies of water
Similar species: C. (H. ) anomalus
is possibly synonymous; differs only by the absence of the two scale rows with longer spines on the head (which was present in my observations) and by scale claspers below the pharynx (which are also present in Ch. novenarius in my observations).)
Particularities: easily delimited by the long spines that emerge from a narrow field
Chaetonotus (H.) novenarius is immediately recognizable by its nine very long large spines.
Ch. novenarius: dorsal
The nine large spines each have two secondary tips and extend beyond the end of the animal’s toes. Ch. novenarius is the Chaetonotus with the longest spines relative to the body length (approx. 2/3 of the body length):
Ch. novenarius: dorsal large spines
Although the scales and spines clearly identify the animal as Ch. novenarius, the ventral scales of the found animal are puzzling:
Ch. novenarius: ventral
Striking are the rectangular scale plates in the pharynx area, which Schwank only shows for the very similar species Ch. anomalus. It is possible that this species is a synonym of Ch. novenarius, as (Schwank, 1990)does not rule out.
*Typical Chaetonotus (Hystricochaetonotus) - here
C. (H. ) persetosus
Ch. murrayi: cross section
Ch. murrayi: dorsal
Ch. murrayi: focus on the spine tips
Ch. murrayi: dorsal scaling of the head / neck area
Ch. murrayi: dorsal scaling of the hind end
Ch. murray: Scales of the ventral intermediate field
Ch. novenarius: dorsal
Ch. novenarius: dorsal large spines
Ch. novenarius: ventral