Chaetonotus (Chaetonotus) microchaetus Preobrajenskaja, 1926

Kånneby, Tobias, 2013, New species and records of freshwater Chaetonotus (Gastrotricha: Chaetonotidae) from Sweden, Zootaxa 3701 (5), pp. 551-588 : 562

Chaetonotus (Chaetonotus) microchaetus Preobrajenskaja, 1926

( Fig. 6 )

Synonyms: Chaetonotus balsaminus Schwank, 1990 [syn: Kisielewski 1997]

Localities: Small pond, Askö, Södermanland (N 58º 49’ 23’’; E 17º 38’ 32’’), May 14, 2009; Sphagnum rock pool, Skarvesäter, Bohuslän, Sweden (N 58º 14’ 23’’; E 11º 22’ 08’’), July 16, 2009; Freshwater rockpool, Östra Båtskäret, Stockholm archipelago (N 59º 44’ 35’’; E 19º 19’ 11’’), September 18, 2007; Runmarö, Stockholm archipelago (N 59º 17’ 22’’; E 18º 47’ 56’’), May 14, 2010; Small stream, Abisko Tourist Station, Abisko (N 68º 21’ 23’’; E 18º 47’ 59’’), July 3, 2010; Wet meadow, Abisko Scientific Research Station, Lapland (N 68º 21’ 18’’; E 18º 48’ 40’’), July 4, 2010; Sphagnum spp. bog at highway E10, Lapland (N 68º 26’ 04’’; E 18º 14’ 53’’), July 1, 2010.

Material: 15 specimens.

TL, 171–241 µm; FL, 25–29 µm; AL, 15–19 µm; PhL, 54–60 µm; MD, 6–9 µm; CW, 14–18 µm; TNC, 29–35; DC, 17–24; DR, 33–36; VLC, 8–12; HS, 3 x 3 µm; NS, 3– 4 x 3 µm; DS, 6– 8 x 4–5 µm; HSp, 2–3 µm; NSp, 2–3 µm; DSp, 3–6 µm; VC, 3–5; VR, ~30–40; VTS, 15– 17 x 6–8 µm.

Head clearly five-lobed with two pairs of cephalic sensory ciliary tufts. Cephalion present. Epi- and hypopleurae well developed. Hypostomium developed as a shield-shaped plate with two teeth. Two pairs of dorsal sensory bristles, anterior pair inserted in posterior neck region at U23–26 and posterior pair emerging from rounded triangular double-keeled scales at U79–83. Furca straight. Adhesive tubes pointing slightly outwards and constituting approximately 3/5 of the total furca length. Dorsal body surface covered by three-lobed scales with more or less rounded anterior edges. Scales with short rather thick simple spines which increase in length toward the posterior end. Scales and spine distribution follows the lateral body outline, only the median columns are more or less straight. Anterior to the furcal base an area with smaller scales with shorter spines. Two to three pairs of longer parafurcal spines, up to 13 µm in length in the Swedish specimens.

Ventrolateral scales and spines similar to those of the dorsal side. Ventral interciliary field with 26–28 transverse scale plates in the pharynx and anterior intestinal region. Rest of intestinal region with rounded keeled scales of different sizes; the 2–3 median scale columns hold the largest scales. Posteriormost row of interciliary scales oval with pronounced keel. Large elongated oval ventral terminal scales with keel. Posterolateral to the ventral terminal scales, 2–3 pairs of spined scales; the median pair with spines up to 8 µm in length. Ventral ciliation in two longitudinal bands that further divide on the head. The inner bands merge just behind the hypostomium.

Mouth subterminal. Pharynx with weak posterior swelling. PhIJ located at U31–34. Intestine straight with anus at U82–86.

All the Swedish specimens were adults mostly in parthenogenetic phase. One specimen, in postparthenogenetic phase, with few bundles of apparently rod-shaped spermatozoa and a horseshoe-shaped X-organ.

Previously reported from Germany (Schwank 1990), Great Britain (Martin 1990), Italy (Balsamo 1983), Poland (Kisielewski 1981), Russia (Preobrajenskaja 1926) and Sweden (Kånneby et al. 2013).

Figures

FIGURE 6. Chaetonotus (C.) microchaetus. A) Habitus. B) Ventral view of neck and anterior trunk region showing transverse scale plates. C) Dorsal view of mid-trunk region showing distribution of scales and spines. Scale bars: A, 25 µm; B and C, 10 µm.