Chaetonotus (Primochaetus) veronicae, Kånneby, Tobias, 2013

Kånneby, Tobias, 2013, New species and records of freshwater Chaetonotus (Gastrotricha: Chaetonotidae) from Sweden, Zootaxa 3701 (5), pp. 551-588 : 581-583

Chaetonotus (Primochaetus) veronicae n. sp.

( Fig. 22 , 23 )

Type locality: Small stream, Abisko Tourist Station, Abisko, Lapland (N 68º 21’ 23’’; E 18º 47’ 59’’), July 3, 2010.

Other localities: Kungsleden, Abisko, Lapland (N 68º 21’ 49’’; E 18º 46’ 64’’), July 3, 2010.

Type material: Photographs of one specimen, available at the Swedish Museum of Natural History, Stockholm, Sweden. Accession number: Holotype, SMNH Type-8446. Photographs of two specimens, available at the Swedish Museum of Natural History, Stockholm, Sweden. Accession number: Paratypes, SMNH Type-8447 and 8448.

Etymology: This species is named in honour of Dr. Veronica Lundgren.

Diagnosis: Small species, 123–125 µm in total body length. Body width 25–30 µm, 18 µm, 28–38 µm and 16– 18 µm at head, neck, trunk and base of furca respectively. Head five-lobed with cephalion and weakly developed pleurae. Furca straight, 18–20 µm in length, with thick rigid adhesive tubes. Dorsal body surface covered by round to suboval overlapping scales, anterior parts of which tend to be fused with the body surface. Scales are distributed in 16–19 dorsal columns with 27–30 scales in each. Each dorsal scale carries a simple hair-like strongly curved spine, originating from, and more or less perpendicular to the posterior part of the scale. Ventrolaterally spines are only slightly curved. Ventral interciliary area with small, round to suboval keeled scales, which fuse with the body surface towards the animal’s anterior end. Ventral terminal scales keeled and suboval in shape and strongly overlapping. Seven to eight simple ventral spines can be seen through the caudal incision. Ventral ciliation in two separate longitudinal bands. Mouth subterminal. Pharynx 34–35 µm in length, widens slightly towards the posterior end.

Description: Small species, 123–125 µm in total body length (holotype 125 µm in total body length). Head clearly five-lobed with two pairs of cephalic sensory ciliary tufts. Anterior pair with approximately 5 cilia, 5–10 µm in length; posterior pair with approximately 5 cilia of which 2–3 are longer, 14–30 µm in length. Cephalion, 14 µm in width. Pleurae weakly developed. Hypostomium developed as a transverse sub-rectangular somewhat shield-shaped plate. Anterior dorsal sensory bristles apparently absent, posterior dorsal sensory bristles emerging from weakly devloped rounded double-keeled scales at U79.

Body width of fairly squeezed specimens, 25–30 µm at the head (U11–13), 18 µm at the neck (U28–30), 28–38 µm at the trunk (U63–65) and 16–18 µm at the base of the furca (U85–88). Head delimited from trunk by a constricted neck. The trunk reaches its maximum width approximately halfway to 2/3 down the length of the body. Furca straight, 18–20 µm in length. Adhesive tubes thick and rigid, 9–10 µm in length.

Dorsal surface covered by round to suboval overlapping scales, the anterior parts of which tend to be fused with the body surface. Scales are distributed in 16–19 dorsal columns with 27–30 scales in each. The total number of scale columns is 30–33. The median dorsal column is more or less straight while scales on either side progressively approach parallelism with the lateral body outline. Developed scales are 2–3 µm in length and 2–3 µm in width and are of similar size all over the body. Scales of the furcal base tend to be more reduced than scales of other parts of the dorsal body surface. Dorsal scales bear simple hair-like spines, up to 9 µm in length, originating from, and more or less perpendicular to, the posterior part of each scale. Moreover spines are strongly curved, relative to the spine axis below the curve, approximately 1/3 of the length from their anchor point. Dorsally this gives the impression that scales are stalked e.g. as in Aspidiophorus (Voigt, 1903) . At the posterior end a pair of slightly curved parafurcal spines, 14–16 µm in length. Ventrolateral scales are smaller but similar in shape to those of the dorsal body surface. Spines of the ventrolateral areas are only slightly curved.

The anterior 2/3 of the ventral interciliary area apparently naked. The posterior third is covered by round to oval small, keeled scales, 1–2 µm in length and 1–2 µm in width. Interciliary scales become more and more fused with the body surface anteriorly, but can be followed to where the body reaches its greatest width (U63–65). In the posterior end a pair of keeled suboval strongly overlapping ventral terminal scales, 6–8 µm in length and 4–5 µm in width. Posterior to the ventral terminals scales 7–8 simple spines (their scales could not be observed), 10–14 µm in length; they are confined within the caudal incision, the outer spines are curved towards the furcal branches, while the median spines are more or less straight or only slightly curved towards the furcal branches. Ventral ciliation in two separate longitudinal bands, with anterior cilia up to 15–20 µm in length.

Mouth subterminal, 4–6 µm in diameter. Pharynx widens slightly towards the posterior end, 34–35 µm in length. PhIJ at U31–34. Intestine straight with anus at U81–82.

The specimens studied were all in parthenogenetic phase.

Taxonomic remarks: It appears that C. (P.) veronicae n. sp. should be affiliated with C. ( Primochaetus ). The main reasons are: (i), the round scales; (ii), spines arise closer to the posterior edges of the scales; (iii), spines increase only slightly in length from anterior to posterior; (iv), all dorsal scales lack keels, and spines originates from a single point. Within the subgenus C. (P.) veronicae n. sp. appears morphologically closest to C. (P.) mutinensis with which it shares the simple thin hair-like spines and the rounded scales. The new species can be separated from C. (P.) mutinensis based on the following characters: (i) the new species have strongly curved spines compared to the gently curved spines in C. (P.) mutinensis ; (ii) the number of dorsal scale columns and scale rows which is greater in C. (P.) veronicae n. sp. (16–19 vs. 9–12 and 27–30 vs. 22–25 respectively); (iii) the scales of the ventral interciliary field which are reduced in the new species compared to the developed scales of C. (P.) mutinensis .

Figures

FIGURE 22. Chaetonotus (P.) veronicae n. sp. A) Habitus, note the thick furcal branches and the strongly curved spines. B) Dorsal view showing distribution of scales. C) Anterior body showing mouth and shape of pharynx. D) Dorsal view of midtrunk region showing bases of spines. E) Ventral view of posteriormost body showing spines between the furcal branches. Scale bars: A, 25 µm; B – E, 10 µm.

FIGURE 23. Chaetonotus (P.) veronicae n. sp., schematic drawing. Dorsal view to the right and ventral view to the left. Scale bar: 10 µm.