Chaetonotus (Primochaetus) acanthodes Stokes 1887

Chaetonotus (Primochaetus) acanthodes Stokes, 1887

(Fig. 16)

Localities: Askö, Södermanland (N 58º 49’ 23’’; E 17º 38’ 32’’), May 14, 2009; Freshwater Rockpool among Sphagnum spp., Hållö, Bohuslän (N 58º 20’ 03’’; E 11º 12’ 50’’), July 14, 2009; Skaftö, Bohuslän (N 58º 14’ 39’’; E 11º 27’ 16’’), July 24, 2009; Artificial pond, Nybro, Småland (N 56º 44’ 89’’; E 15º 54’ 27’’), June 28, 2008; Ängelstorp, Småland (N 57º 20’ 08’’; E 16º 28’ 46’’), May 1, 2010; Lake with Sphagnum spp., Abisko, Lapland (N 68º 21’ 19’’; E 18º 49’ 21’’) July 6, 2010; Sphagnum spp. bog at highway E10, Lapland (N 68º 26’ 04’’; E 18º 14’ 53’’), July 1, 2010.

Material: 12 specimens.

TL, 128–145 µm; FL, 15–20 µm; AL, 10–11 µm; PhL, 31–34 µm; MD, 6–8 µm; CW, 12–14 µm; TNC, 18–20; DC, 10–12; DR, 22–25; VLC, 6–8; HS, 2– 4 x 2–4 µm; NS, 2– 4 x 2–5 µm; DS, 6– 7 x 6–7 µm; HSp, 2–3 µm; NSp, 0–3 µm; DSp, 0–4 µm; Gsp, 10–14 µm; VC, 8–9; VR, ~25–30.

Head truncated, weakly five-lobed with two pairs of short cephalic sensory ciliary tufts. Cephalion and pleurae developed. Hypostomium developed as a thin rectangular plate. Two pairs of dorsal sensory bristles, anterior pair sometimes absent. Anterior pair inserted at U26 and posterior pair emerging from rounded double-keeled scales at U77–80. Furca straight with adhesive tubes constituting half to 2/3 of the total furca length. Dorsal body surface covered with oval to circular, strongly overlapping keeled scales with or without simple spines. Spines occasionally completely absent from the neck region and the trunk region posterior to the girdle. The girdle is formed by 7–12 scales positioned approximately 2/3 down the length of the body and provided with thick simple spines. Two pairs of parafurcal spines, 10–16 µm in length, in the posterior end.

Ventrolateral scales similar to the dorsal ones, but with longer spines especially developed in the girdle region. Ventral interciliary field covered by round to suboval scales with short simple spines; spines are reduced towards the anterior end and in the pharynx region scales are generally only keeled. Posterior part of interciliary field covered by four elongated oval scales with fine simple spines visible between the furcal branches. Ventral ciliation in two separate longitudinal bands that widen and further divide in the head region.

Large subterminal mouth. Pharynx widens towards the posterior end, with weak posterior swelling. PhIJ at U23–24. Intestine straight with anus at U83–84.

The Swedish specimens were all in parthenogenetic phase and fell within the ranges previously reported in the literature. In particular they agree very well with Polish and Finnish specimens (see Kisielewski 1981). Previously reported from Finland (Kisielewski 1981), Poland (Kisielewski 1981), Russia (Tretjakova 1989), Romania (Rudescu 1967), Switzerland (Greuter 1917), Sweden (Kånneby et al. 2013), Brazil (Kisielewski 1991) and USA (Stokes 1887).