Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887

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

Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887

( Fig. 15 )

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.

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 U76–80. 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 U31–33. Intestine straight with anus approximately at U85–86.

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).

Figures

FIGURE 15. Chaetonotus (H.) spinulosus. A) Dorsal view showing distribution of scales and spines. Note that the head and neck regions lack scales. B) Ventral view showing locomotory ciliation and ventral terminal scales. Scale bars: 10 µm.