Chaetonotus (Hystricochaetonotus) euhystrix Schwank 1990

Chaetonotus (Hystricochaetonotus) euhystrix Schwank, 1990

(Fig. 12)

Localities: Storlien W, Jämtland (N 63º 19’ 06’’; E 12º 05’ 22’’), July 10, 2008; Wet meadow, Abisko Scientific Research Station, Lapland (N 68º 21’ 18’’; E 18º 48’ 40’’), July 4, 2010.

Material: 2 specimens.

TL, 182 µm; FL, 29 µm; AL, 17 µm; PhL, 52 µm; MD, 8 µm; CW, ~10 µm; TNC, 13; DC, 7; DR, 15–17; VLC, 6; HS, 4– 6 x 3–8 µm; NS, 8 x 10 µm; DS, 12 x 12 µm; HSp, 6–12 µm; NSp, 20 µm; DSp, 45–60 µm; VC, 7– 8; VTS, 9–10 x 4 µm.

A large Hystricochaetonotus. Head rounded to weakly five-lobed. Two pairs of sensory ciliary tufts, the posterior pair with very long cilia, up to 30 µm in length. Cephalion relatively small. Hypostomium absent. At least posterior dorsal sensory bristles present, emerging from specialized sub-triangular double-keeled scales. Furca straight with adhesive tubes constituting approximately 3/5 of the total furca length. Dorsal surface covered by three-lobed scales with barbed spines. Spines increase drastically in length from anterior to posterior. At least one pair of dorsal spines clearly overshoots the furca and another pair reaches the tip of the furcal branches. Accessory points originate approximately 2/3 up the length of the spine.

Ventrolateral scales similar in shape to the dorsal scales but smaller in size. Ventrolateral spines finer than the dorsal spines. Interciliary area covered by keeled to smooth rounded scales. A pair of ventral terminal keeled scales, apparently without spines in the posterior end.

Mouth terminal. Pharynx widens towards the PhIJ at U30. Intestine straight with anus at U81.

The Swedish material consisted of one adult specimen in parthenogenetic phase and one juvenile specimen. The Swedish specimen disagrees with the original description by Schwank (1990) in that they have two rounded double-keeled scales on the base of each furcal branch. These scales are in turn surrounded by three pairs of elongated three-lobed scales much like in C. (H.) hystrix. Moreover, in the posterior trunk region a pair of threelobed keeled scales without spines present just anterior to the double-keeled scales anchoring the posterior sensory bristles. The Swedish adult specimen is larger than the German specimens. According to Schwank (1990), C. (H.) euhystrix is a variable species, so, notwithstanding the foregoing deviations from Schwank’s description, these specimens are tentatively assigned to that species.

Previously reported from Germany (Schwank 1990).