Chaetonotus (Chaetonotus) naiadis Balsamo & Todaro 1995

Chaetonotus (Chaetonotus) naiadis Balsamo & Todaro, 1995

(Fig. 7)

Localities: Saltö, Bohuslän (N 58º 52’ 21’’; E 11º 07’ 34’’), November 13, 2008; Abisko, Lapland (N 68º 21’ 23’’; E 18º 47’ 59’’), July 5, 2010.

Material: 3 specimens.

TL, 137–140 µm; FL, 14–18 µm; AL, 7–8 µm; PhL, 32–33 µm; MD, 4–5 µm; CW, 12–13 µm; TNC, 28–31; DC, 20–21; DR, 27–28; VLC, 8–11; HS, 2 x 2 µm; NS, 2– 3 x 2–3 µm; DS, 3– 4 x 2–3 µm; HSp, 1–2 µm; NSp, 1– 2 µm; DSp, 1–2 µm; VC, 5–6; VTS, 5 x 3 µm.

Five-lobed head with two pairs of cephalic sensory ciliary tufts; anterior pair with mostly short cilia, but one cilium substantially longer than the others. Hypostomium developed as a small sub-rectangular plate. Two pairs of dorsal sensory bristles; anterior pair inserted at U28 and posterior pair emerging from rounded triangular doublekeeled scales at U78–79. Furca straight with adhesive tubes constituting approximately half of the total furca length. Dorsal body surface covered by small three-lobed scales with minute simple spines. Scales and spines only increase slightly in size towards the posterior end. An area anterior to the caudal incision and between the posterior sensory bristles has scales spaced wider apart than the rest of the dorsal surface.

Ventrolateral scales and spines similar to those of the dorsal surface, but sometimes with spines reaching lengths up to 3–4 µm. Ventral interciliary area covered by small rounded keeled scales that seem to fuse with the body surface anterior to the 2 or 3 posteriormost rows. Ventral terminal scales suboval to sub-rectangular and keeled. Ventral ciliation in two separate longitudinal bands, that widen on the head.

Mouth subterminal. Pharynx without swellings, only widens slightly towards the PhIJ at U28–31. Intestine straight with anus at U85–87.

The Swedish specimens were all adults in parthenogenetic phase. Compared to the description by Balsamo & Todaro (1995) they are just below the upper limits of the total body length (140 µm) reported for the species. Previously reported from Italy (Balsamo & Todaro 1995).