Chaetonotus (Hystricochaetonotus) aemilianus Balsamo 1978

Chaetonotus (Hystricochaetonotus) aemilianus Balsamo, 1978

(Fig. 11)

Localities: Gravel pit, Åhus, Skåne (N 55º 55’ 43’’; E 14º 15’ 08’’), April 10, 2009; 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: 4 specimens.

TL, 112–122 µm; FL, 16–18 µm; AL, 9–10 µm; PhL, 28–29 µm; MD, 4–5 µm; TNC, ~14; DC, 8–9; DR, ~12; VLC, 5–6; DS, 5– 7 x 4–5 µm; DSp, 5–6 µm; VC, 7; VTS, 8 x 3–4 µm.

Small species. Head rounded to weakly five-lobed with two pairs of cephalic sensory ciliary tufts. Hypostomium absent. Two pairs of dorsal sensory bristles present, the posterior pair emerging from specialized sub-triangular double-keeled scales at U79. Furca straight with adhesive tubes constituting approximately half of the total furca length. Head and neck regions may be naked or covered by smaller scales similar to those of the trunk region (Balsamo 1980). Dorsal trunk surface covered by three-lobed to pentagonal scales, in general with short simple spines; however, 7–8 larger scales in the trunk region bear longer barbed spines, 18–22 µm in length, while others may be deprived scales altogether. Anterior to the furcal branches a pair of double-keeled round to sub-rectangular scales sometimes present, surrounded by four pairs of elongated three-lobed scales, similar to those of C. (H.) hystrix.

Ventral interciliary area can be naked or covered by round smooth scales (Balsamo 1980). A pair of keeled ventral terminal scales present. Ventral ciliation in two separate longitudinal bands.

Mouth terminal to subterminal. Pharynx with weak anterior and posterior swellings. PhIJ at U27–29. Intestine straight with anus at U82–83.

The Swedish specimens were in parthenogenetic or post-parthenogenetic phase. Two specimens had a well developed horseshoe-shaped X-organ. One of them also showed packets of apparently rod-shaped spermatozoa anterior to the X-organ. C. (H.) aemilianus is one of the most variable gastrotrich species and four different forms have been described (Balsamo 1980). The Swedish specimens had a naked head region and a more or less naked neck region. In the trunk region they had 7 long barbed dorsal spines and posteriorly a pair double-keeled scales at the base of the furcal appendages. The interciliary field was covered by rounded smooth scales. Considering those features the material studied appear most similar to form B or D (Balsamo 1980).

Previously reported from Italy (Balsamo 1978, 1980), Germany (Schwank 1990), Sweden (Kånneby et al. 2013) and Canada (Schwank 1990).