Chaetonotus (Primochaetus) mutinensis Balsamo 1977

Chaetonotus (Primochaetus) mutinensis Balsamo, 1977

(Fig. 20)

Localities: Norra Djurgården, Stockholm (N 59º 22’ 06’’; E 18º 04’ 15’’), May 14, 2008; Sphagnum spp. bog at highway E10, Lapland (N 68º 26’ 04’’; E 18º 14’ 53’’) July 1, 2010; Small stream, Abisko Tourist Station, Abisko (N 68º 21’ 23’’; E 18º 47’ 59’’), July 3, 2010; Saltö, Bohuslän (N 58º 52’ 21’’; E 11º 07’ 34’’), November 13, 2008; Östra Båtskäret, Stockholm archipelago (N 59º 44’ 35’’; E 19º 19’ 11’’), September 18, 2007.

Material: 8 specimens.

TL, 168–207 µm; FL, 23–26 µm; AL, 13–16 µm; PhL, 53–56 µm; MD, 6–8 µm; CW, 14–16 µm; TNC, 17–18; DC, 9–10; DR, ~30; VLC, 8; HS, 3– 4 x 3–4 µm; NS, 4 x 3–4 µm; DS, 8 x 5–6 µm; HSp, 5–9 µm; NSp, 5–12 µm; DSp, 18–22 µm; VC, 6–7; VTS, 13– 16 x 7–8 µm.

Head clearly five-lobed with two pairs of cephalic sensory ciliary tufts. Cephalion well developed. Shieldshaped hypostomium with two teeth. Anterior and posterior dorsal sensory bristles present, posterior pair emerging from double-keeled scales at U82. Furca more or less straight with adhesive tubes constituting approximately 2/3 of the total furca length. Dorsal body surface covered with rounded scales with fine, gently curved, simple spines. Spines increase in length towards the posterior end. A dorsal area anterior to the caudal incision with smaller scales and shorter spines, not unlike C. (C.) maximus.

Ventrolateral area with scales and spines similar to those on the dorsal surface, but scales closest to the ventral ciliary bands smaller in size. In the head- and neck region lateral spines are longer than spines of the same region on the dorsal surface. Ventral interciliary area with round smooth scales. The scales of the last two interciliary rows oval to weakly three-lobed, with keels and a very short simple spines. Ventral terminal scales elongate oval and keeled with short simple spines.

Mouth subterminal. Pharynx widens posteriorly. PhIJ at U32–35. Intestine straight with anus at U84–85.

According to Schwank (1990) there seems to be two non-overlapping morphological forms of C. (P.) mutinensis, which differs in size. The Swedish specimens are all above 160 µm in total body length, which apparently is the reported lower size limit for German and Canadian specimens. Specimens collected on the Swedish west coast do not have the posterior pair of dorsal sensory bristles emerging from double-keeled scales. However, specimens from northern Sweden show these scales, and one of them is just above the total body length reported in the literature. All Swedish specimens were adults in parthenogenetic phase.

Previously reported from Germany (Schwank 1990), Italy (Balsamo 1977), Sweden (Kånneby et al. 2009) and Canada (Schwank 1990).