Chaetonotus (Chaetonotus) heterospinosus Balsamo 1977

Chaetonotus (Chaetonotus) heterospinosus Balsamo, 1977

(Fig. 4)

Localities: Storlien E, Jämtland (N 63º 18’ 42’’; E 12º 06’ 43’’), July 10, 2008; Storlien W, Jämtland (N 63º 19’ 06’’; E 12º 05’ 22’’), July 10, 2008; Pond with Nymphaea sp., Bergianska Trädgården, Stockholm (N 59º 22’07’’; E 18º 02’ 41’’) June 19, 2008; Freshwater Sphagnum spp. rockpool, Kristineberg, Bohuslän (N 58º 14’ 50’’; E 11º 26’ 22’’), July 21, 2009; Small rockpool, Fiskebäckskil, Bohuslän (N 58º 14’ 39’’; E 11º 27’ 16’’), July 23, 2009.

Material: 7 specimens.

TL, 193–240 µm; FL, 26–35 µm; AL, 20–26 µm; PhL, 55–70 µm; MD, 7–8 µm; CW, 18 µm; TNC, ~16; DC, 9–11; DR, ~22; VLC, ~6; HS, 3 x 5 µm; NS, 4– 5 x 6 µm; DS, 10– 15 x 10–15 µm; HSp, 6–7 µm; NSp, 6–7 µm; DSp, 20–32 µm; VC, 5–6; VR, ~22; VTS, 12– 14 x 6–8 µm.

Five-lobed head with two pairs of cephalic sensory ciliary tufts. Cephalion well developed. Hypostomium present. Anterior and posterior dorsal sensory bristles present, posterior pair emerging from sub-triangular doublekeeled scales at U76–78. Furca straight with adhesive tubes contributing to approximately 3/4 of the total furca length. Dorsal body surface covered by three-lobed to pentagonal scales with simple or barbed spines. In the head and neck region scales are more or less rectangular to pentagonal in shape. Anteriormost scales, just behind the cephalion, keeled and with or without spines. Dorsal and lateral spines increase in length towards the posterior end. In the posterior end a pair of barbed parafurcal spines that almost reach the tip of the adhesive tubes. Between the furcal branches 4–7 barbed spines originating from the dorsal side.

Ventrolateral scales and spines similar to those of the dorsal side. Ventral interciliary field covered with round to oval keeled scales. Ventral terminal scales large, suboval and keeled. Posterior to these a pair of three-lobed to sub-triangular keeled scales with short fine spines. Ventrally at the base of each furcal branch several small keeled scales; the keel of each scale sometimes drawn out to form a spine. Ventral ciliation in two separate longitudinal bands that widen on the head.

Mouth terminal. Pharynx large and muscular. PhIJ at U31–34. Intestine straight with anus at U84–85.

C. (C.) heterospinosus is a very variable species. In addition to the nominal form, Balsamo (1980) subsequently described three other forms. These forms differ most notably in the scale pattern of the interciliary field. The Swedish specimens are close to the nominal form, with rather large round to oval keeled scales in the interciliary area but show barbed dorsal spines.

Previously reported from Denmark (Grilli et al. 2010), France (Grilli et al. 2008), Italy (Balsamo 1978; 1980), Russia (Grilli et al. 2010) and Korea (Lee & Chang, 2000).