Chaetonotus (Primochaetus) heideri Brehm 1917

Chaetonotus (Primochaetus) heideri Brehm, 1917

(Fig. 18)

Localities: Lake Ånnsjön, Jämtland (N 63º 15’ 65’’; E 12º 27’ 03’’), July 8, 2008; Storlien E, Jämtland (N 63º 18’ 42’’; E 12º 06’ 43’’), July 10, 2008; Snasahögarna, Jämtland (N 63º 12’ 39’’; E 12º 18’ 19’’), July 7, 2008; Lake Gevsjön, Jämtland (N 63º 22’ 14’’; E 12º 42’ 10’’), July 10, 2008; Freshwater Rockpool among Sphagnum spp., Hållö, Bohuslän (N 58º 20’ 03’’; E 11º 12’ 50’’), July 14, 2009; Saltö, Bohuslän (N 58º 52’ 21’’; E 11º 07’ 34’’) September 13, 2008; Skaftö, Bohuslän (N 58º 14’ 39’’; E 11º 27’ 16’’), July 23, 2009; Bog at highway E10, Lapland (N 68º 25’ 58’’; E 18º 23’ 00’’), July 1, 2010; A small pond close to lake Torneträsk at Abisko Scientific Research Station, Lapland (N 68º 21’ 19’’; E 18º 49’ 21’’), June 30, 2010.

Material: 10 specimens.

TL, 113–195 µm; FL, 20–25 µm; AL, 15–18 µm; PhL, 36–44 µm; MD, 8–10 µm; TNC, 16–17; DC, 7–9; DR, ~20; VLC, 8; HS, 3– 4 x 3–4 µm; NS, 3– 8 x 3–12 µm; DS, 7– 12 x 9–16 µm; HSp, 4–9 µm; NSp, 10–16 µm; DSp, 16–36 µm; VC, 5–7.

A very variable species (Balsamo 1980; Schwank 1990). Head rounded to weakly five-lobed with two pairs of cephalic sensory ciliary tufts. Cephalion and pleurae weakly developed. Hypostomium sometimes developed as a more or less concave bar (Schwank 1990). Two pairs of dorsal sensory bristles; anterior pair inserted between scales, posterior pair emerging from rounded pentagonal double-keeled scales. Furca relatively short with adhesive tubes constituting 2/3–4/5 of the total furca length. Dorsal surface covered with heart-shaped to pentagonal scales, sometimes with more or less well developed double anterior edge (Schwank 1990). Scales increase in size from the head region to mid-posterior trunk region with a subsequent decrease towards the caudal end. Barbed spines originate from approximately the center of each scale, increasing in length from anterior to posterior. The posteriormost spines can overshoot the furca.

Ventrolateral scales similar in appearance to those of the dorsal surface, decreasing in size medially. Ventral interciliary field covered with numerous keeled rounded scales or several columns (5–7) of rounded spined scales (Balsamo 1980). At the posterior end of the interciliary field 2–4 scales with very long simple spines sometimes present. The medial spines can be longer than the furca.

Mouth large. Pharynx with weak swellings at both ends. PhIJ at approximately U26. Intestine straight with anus at approximately U84.

The Swedish specimens were all adults in parthenogenetic phase. They showed a high variability in size of scales and length of spines. According to Balsamo (1980) C. (P.) heideri is a very variable species. The Swedish specimens agree more or less with form C and D (Balsamo 1980). It is very likely that C. (P.) heideri is a complex of closely related morphological species. The species is fairly common and could serve as a model organism to study species delimitation within freshwater chaetonotid gastrotrichs.

Previously reported from France (Grilli et al. 2008), Germany (Brehm 1917), Great Britain (Martin 1990?), Italy (Balsamo 1983), Poland (Kisielewski 1981), Romania (Rudescu 1967), Russia (Preobrajenskaja 1926), Sweden (Kånneby et al. 2009; 2013), Brazil (Kisielewski 1991), Canada (Schwank 1990) and USA (Emberton 1981).