Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887, Stokes, 1887

Kånneby, Tobias, 2013, New species and records of freshwater Chaetonotus (Gastrotricha: Chaetonotidae) from Sweden, Zootaxa 3701 (5), pp. 551-588: 573-574

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Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887


Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887  

( Fig. 15 View FIGURE 15 )

Localities: Storlien E, Jämtland (N 63 º 18 ’ 42 ’’; E 12 º 06’ 43 ’’), July 10, 2008; Storlien W, Jämtland (N 63 º 19 ’ 06’’; E 12 º 05’ 22 ’’), July 10, 2008.

Material: 3 specimens.

TL, 88–100 µm; FL, 11–14 µm; AL, 6–7 µm; PhL, 24–26 µm; MD, 4–5 µm; CW, 8–9 µm; TNC, 12–14; DC, 8–10; DR, 10–12; VLC, 4; NS, 3– 4 x 3–4 µm; DS, 5– 7 x 4–5 µm; NSp, 2–3 µm; DSp, 2–3 µm; VC, 5–6.

One of the smallest gastrotrich species, together with Heterolepidoderma lamellatum Balsamo & Fregni, 1995   and Ichthydium podura (Müller, 1773)   , with a total length of 60–100 µm (Schwank 1990; this study). Head weakly five-lobed with two pairs of cephalic sensory ciliary tufts. Cephalion thin and weakly developed. Hypostomium absent. Two pairs of dorsal sensory bristles, posterior pair emerging from rounded triangular double-keeled scales at U 76–80. Furca short and straight, with adhesive tubes constituting approximately half of the total furca length. Anterior dorsal surface (head and neck) occasionally covered by three-lobed to pentagonal scales, but can also lack these cuticular structures (Schwank 1990). Dorsal trunk surface covered by three-lobed scales with short simple spines. In the mid-rear trunk region 4–8 long barbed spines, 18–26 µm in length, usually distributed in 2–3 alternating rows; other scales of the same area lack spines (Schwank 1990).

Ventrolateral areas covered by scales similar to those of the dorsal surface. Ventral interciliary field naked (Schwank 1990). Ventral ciliation in two separate longitudinal bands.

Mouth subterminal. Pharynx widens towards the posterior end. PhIJ at U 31–33. Intestine straight with anus approximately at U 85–86.

The Swedish specimens in general agree well with data reported in the literature. However, the interciliary area is covered by weakly developed round smooth scales as opposed to the naked interciliary field reported in the literature (Schwank 1990). This is a feature that may have been overlooked in the past. Swedish specimens have 8 long barbed spines and are very similar to the specimens found in Breitecke/Schlitz, Germany by Schwank (1990). In these specimens the longer spines are distributed in 3 rows with 6 spines in the outer columns and 2 spines in the median column. The posteriormost median spines can be seen at the caudal incision between the furcal branches.

Previously reported from Bulgaria (Valkanov 1937), Estonia (Järvekülg 1961), Germany (Schwank 1990), Great Britain (Martin 1990), Hungary (Varga 1949), Italy (e.g. Mola 1932; Balsamo 1983), Poland (Roszczak 1968), Romania (Rudescu 1967), Russia (Preobrajenskaja 1926), Ukraine (Jakubski 1919), India (Naidu & Rao 2004), USA (Stokes 1887; Robbins 1973).