Chaetonotus (Chaetonotus) maximus Ehrenberg 1838

Chaetonotus (Chaetonotus) maximus Ehrenberg, 1838

(Fig. 5)

Synonyms: Chaetonotus gracilis Gosse, 1864 [syn. Zelinka 1889; see also Balsamo et al. 2009]

Localities: Pond with Nymphaea sp., Bergianska Trädgården, Stockholm (N 59º 22’ 07’’; E 18º 02’ 41’’) June 19, 2008; Ängelstorp, Småland (N 57º 20’ 08’’; E 16º 28’ 46’’), May 1, 2010; Sphagnum spp. bog at highway E10, Lapland (N 68º 26’ 04’’; E 18º 14’ 53’’), July 1, 2010; Gravel pit, Åhus, Skåne (N 55º 55’ 43’’; E 14º 15’ 08’’), April 10, 2009.

Material: 4 specimens.

TL, 201–203 µm; FL, 25–27 µm; AL, 15–18 µm; PhL, 57–63 µm; MD, 7–8 µm; CW, 14–18 µm; TNC, 20–21; DC, 12–13; DR, ~30; VLC, 8; HS, 2– 3 x 2–4 µm; NS, 4– 5 x 4–6 µm; DS, 6– 8 x 4–6 µm; HSp, 4–8 µm; NSp, 6–12 µm; DSp, 12–20 µm; VC, 7–8; VTS, 16–18 x 8 µm.

Head clearly five-lobed with two pairs of cephalic sensory ciliary tufts. Large cephalion, epi- and hypopleurae. Hypostomium developed as a more or less shield-shaped transverse plate with two teeth. Two pairs of dorsal sensory bristles present, posterior pair emerging from specialized double keeled scales at U85–87. Furca straight. Adhesive tubes constituting approximately 3/5 of the total furca length. Dorsal body surface covered by arrowhead-shaped three-lobed scales. In the head and neck regions the proximal parts of the scales are more rounded than in the trunk region. Scales bear simple spines that increase in length from anterior to posterior. An area just anterior to the furca base with smaller scales and spines. Five stout spines present on the base of the furcal branches and at the caudal incision. One to two pairs of thick parafurcal spines, that reach approximately halfway down the furcal branches.

Ventrolateral scales and spines similar to those of the dorsal surface. Ventral interciliary field with 9–10 transverse scale plates in the pharynx region. Interciliary scales of the intestinal area rounded and keeled. Posteriormost scale rows oval with short spines. Ventral terminal scales large, elongated and keeled with short spines. Ventral ciliation in two separate longitudinal bands that further divide on the head.

Mouth subterminal. Pharynx with very weak posterior swelling. PhIJ at U32–35. Intestine straight with anus at U82–84.

The Swedish specimens were all in parthenogenetic phase and mostly agree well with literature data. However, one specimen showed spines that appeared shorter compared to the other two specimens.

Previously reported from Austria (Zelinka 1889), Belgium (Dumont 1968), Bulgaria (Valkanov 1937), Denmark (Grilli et al. 2010), Estonia (Järvekulg 1961), France (d’Hondt 1967), Germany (Remane 1936; Schwank 1990), Great Britain (Martin 1981), Hungary (Varga 1949), Iceland (De Coninck 1939), Italy (e.g. Marcolongo 1910; Balsamo 1983), Poland (e.g. Kisielewski 1981), Romania (Rudescu 1967), Russia (Preobrajenskaja 1926), Spain (Real 1940), Sweden (Hofsten 1923; Kånneby et al. 2013), Switzerland (Greuter 1917), Ukraine (Jakubski 1919), Algeria (d’Hondt 1977), Canada (Schwank 1990), Japan (Saito 1937), New Guinea (Daday 1901) and USA (Stokes 1887). According to Fauna Europaea (www.faunaeur.org) also present in Czech Republic, Greece and Northern Ireland.