Chaetonotus (Chaetonotus) benacensis Balsamo & Fregni, 1995

Kånneby, Tobias, 2013, New species and records of freshwater Chaetonotus (Gastrotricha: Chaetonotidae) from Sweden, Zootaxa 3701 (5), pp. 551-588 : 557-559

Chaetonotus (Chaetonotus) benacensis Balsamo & Fregni, 1995

( Fig. 2 )

Localities: Lake Siljan, Dalarna (N 60º 53’ 04’’; E 15º 06’ 47’’), July 6, 2008.

Material: 2 specimens.

TL, 101–106 µm; FL, 15 µm; AL, 8–9 µm; PhL, 24–25 µm; MD, 3–4 µm; CW, 10 µm; DC, 7; DR, 13–15; HS, 3 x 2 µm; NS, 4 x 3 µm; DS, 6 x 4 µm; HSp, 3 µm; NSp, 3–4 µm; DSp, 6–9 µm; VC, 3–4; VTS, 8– 9 x 2 µm.

Small species. Head weakly five-lobed with two pairs of cephalic sensory ciliary tufts. Hypostomium developed as a trapezoidal plate behind mouth. Furca straight. Adhesive tubes constituting almost 2/3 of the total furca length. Anterior and posterior dorsal sensory bristles present, posterior pair emerging from sub-triangular double keeled scales at U76–77. Dorsal body surface covered by three-lobed scales with barbed spines. Four scales in the mid-posterior trunk region with longer simple spines. Four pairs of keeled scales, with very short spines, at the base of each furcal appendage. Scales and spines increase in size towards the posterior end.

Ventral interciliary area with mostly smooth scales, posteriormost row keeled. Ventral terminal scales rounded rectangular and keeled. In addition four smaller keeled ventral scales at the caudal incision. Ventral ciliation in two separate longitudinal bands, which widen on the head.

Pharynx slightly swollen at both ends. PhIJ at U29. Intestine straight with anus at U81.

The Swedish specimens were in parthenogenetic phase and correspond well to the original description by Balsamo & Fregni (1995). However, parafurcal spines appear more pronounced. In addition one of the specimens show a double keeled scale, not unlike the ones found in Chaetonotus (H.) hystrix Metschnikoff, 1865 , at the base of the furcal appendage. The double-keeled scale could only be seen on one side of the animal. Because of the 4 dorsal long simple spines and the trapezoidal hypostomium together with other morphometric data the Swedish specimens are considered C. (C.) benacensis .

Previously reported from Italy (Balsamo & Fregni 1995) and Sweden (Kånneby et al. 2009).

Chaetonotus (Chaetonotus) daphnes Balsamo & Todaro, 1995 ( Fig. 3 )

Localities: Storlien E, Jämtland (N 63º 18’ 42’’; E 12º 06’ 43’’), July 10, 2008; Skarvesäter, Bohuslän (N 58º 14’ 41’’; E 11º 22’ 63’’), July 16, 2009; Lake Trösvattnet, Västmanland (N 59º 33’ 21’’; E 14º 29’ 23’’) December 1, 2007; Gravel pit, Åhus, Skåne (N 55º 55’ 43’’; E 14º 15’ 08’’) April 10, 2009.

Material: 5 specimens.

TL, 147–176 µm; FL, 18–20 µm; AL, 8–10 µm; PhL, 38–42 µm; MD, 7 µm; CW, 11–14 µm; TNC, 56–61; DC, 28–35; DR, 30–35; VLC, 20–22; HS, 1– 2 x 0.5–1 µm; NS, 1.5– 3 x 0.5–1 µm; DS, 1.5– 3 x 0.5–1 µm; HSp, 1– 2 µm; NSp, 1–2 µm; DSp, 1–2 µm; VC, 8–10; VTS, 7 x 4 µm.

Five-lobed head with two pairs of cephalic sensory ciliary tufts of equal length. Large cephalion. Anterior and posterior dorsal sensory bristles present, posterior pair emerging from rounded three-lobed double keeled scales at U82–84. Furca short and straight with thick adhesive tubes. Dorsal surface covered by small three-lobed keeled scales, with very short simple spines. Furcal base with three pairs of larger keeled scales that lack spines.

Ventral interciliary area covered with small suboval scales with short spines. Ventral terminal scales keeled and suboval in shape. Ventral ciliation in two separate longitudinal bands.

Mouth terminal. Pharynx widens towards the posterior end. PhIJ at U28–29. Intestine straight with anus at U86–88.

The Swedish specimens, all in parthenogenetic phase, agree well with the description of Balsamo & Todaro (1995). One specimen showed dimensions and morphometric characters just above the literature data reported for this species. C. (C.) daphnes appears to be quite common, at least in Sweden, but may have been mistaken for Heterolepidoderma in the past because of the very short spines that resembles keels.

Previously reported from Italy (Balsamo & Todaro 1995) and Sweden (Kånneby et al. 2013).

Figures

FIGURE 2. Chaetonotus (C.) benacensis. A) Habitus. B) Dorsal view showing distribution of scales and spines. Scale bars: 10 µm.

FIGURE 3. Chaetonotus (C.) daphnes. A) Dorsal view of anterior body showing head with cephalion, pleurae and scales of the head, neck and anterior trunk region. B) Dorsal view of posterior body showing distribution of scales and scales of the furcal base. C) Ventral view of posterior body showing ventral terminal scales and scales of the interciliary area. D) Detail of dorsal scales. Scale bars: A, 25 µm; B and C, 10 µm; D, 5 µm.