(Primochaetus)

90 - 210 µm
Scales single lobed without keels and cutouts
thick, straight spines at the posterior end of the scales (rarely curved)
all spines +/- same length, length increases slightly towards the back
sometimes groups with elongated spines

Species:

21 Species:

Chaetonotus (P. ) acanthocephalus

100 µm - 148 µm
Dorsal scales: 5 rows of 15-18 transverse oval scales (5 x 10 µm) each, not touching; on head dorsally and laterally 5-7 characteristic spiny scales; small spines 6-7 µm; groups of large spines 8-22 µm.
Ventral scales: Ventral intermediate field on head 3 touching plates; otherwise elliptical plates; in gut region sometimes 3 deer of smaller elliptical plates.
Particularities: very variable with respect to spine size - possibly a number of subspecies

Chaetonotus (P. ) acanthodes

124 µm - 159 µm
Dorsal scales: 10 rows of 20-25 strongly overlapping, rounded triangular scales (5 µm - 8.5 µm) with strongly convex margin (margin appears double) with short spines (7 µm); 7 - 12 simple girdle spines (6.5 µm - 16.5 µm) in alternating rows; scales behind spine girdle mostly without spines
Ventral scales: 4 elongated terminal plates with keel; 8-9 rows of small keel scales
Particularities: Spiked belt and double scale edge

Chaetonotus (P. ) armatus

Chaetonotus (P. ) arquatus

Chaetonotus (P. ) brachyurus

Chaetonotus (P. ) chuni

Chaetonotus (P. ) cordiformis

190 µm - 225 µm
Dorsal scales: 7 rows of fe 20 thin, transverse-oval to obovate scales, only slightly touching each other; spines (10-39 µm) originate slightly behind scale center; secondary tip relatively far from distal end; three pairs of long lateral spines (34-46 µm) overhang toes by twice their length; between toes 3 dorsal spines slightly overhanging toes
Ventral scales: Ventral intermediate field with +11 rows of short spiny tiny scales
Particularities: brood care: decorating the eggs with detritus; var. bernensis has no secondary tips