Chaetonotus (Chaetonotus)

Kolicka, Małgorzata, Kisielewski, Jacek, Nesteruk, Teresa & Zawierucha, Krzysztof, 2013, Gastrotricha from the Poznań Palm House — one new subgenus and three new species of freshwater Chaetonotida (Gastrotricha), Zootaxa 3717 (2), pp. 231-279 : 260-262

Chaetonotus (Chaetonotus) sp. 2 ( Table 9)

Locality: Site 3; session III.

Material: 1 sample, 1 adult specimen, photographed.

Short description: The species is of medium size. It has a five–lobed parabolic head, separated from the wider part of the trunk by a distinct constriction of the neck. The cephalion, epipleuria and hypopleuria are separated by deep indentations. All cephalic plates are well visible in the head outline. The epipleuria and the hypopleuria are large and of equal size. The kidney–shaped hypostomium is small and narrow and has notch on the posterior edge. On the head there are two pairs of cephalic ciliary tufts with three cilia in the anterior and four in the posterior tuft. The mouth ring is situated ventrally. The pharynx has very strong dilatations at the ends (the posterior wider than the anterior). The furca base is clearly indicated by constriction. The furca has a tong shape and adhesive tubes pointed inwards. The posterior pair of the dorsal sensory bristles is anchored by small double–keeled scales. The whole body, except for the ventral interciliary field, is covered with three–lobed scales, with distinct keels and long spines. The scales are arranged in 18 alternating longitudinal rows, 26 scales in each row. They are triangular in shape, with distinct keels and very deep posterior notches. There are large spaces between the scales in a transverse row; scales in longitudinal alternating row are situated close to one another. On the head the scales begin directly behind the cephalion and the pleurs. The spines have strong curvature, but without lateral denticles. The length of spines increases gradually from the head through neck to ca. ¾ of the body length. The longest spines are considerably longer than the others, arising in a row at ca. ¾ down the length of the body. The posterirmost lateral spines are shorter than the longest trunk spines. The ventral interciliary field is covered with triangular scales with keels and spines. The ventral terminal scales are elliptical in shape, with posterior notches, keels, and straight thick spines. Ocellar granules are absent.

Differential diagnosis: C. (C.) sp. 2 most resembles species belonging to the subgenus Primochaetus viz. Chaetonotus (P.) acanthodes Stokes, 1887 , and Chaetonotus (P.) macrolepidotus macrolepidotus Greuter, 1917, although it uniquely belongs to the subgenus Chaetonotus . A similar species is also Chaetonotus (Chaetonotus) sphagnophilum Kisielewski, 1981 .

Character Specimen Body length 136.5 Pharynx length 30.5

Width of anterior pharynx thickening (a) 9.5

Width of pharynx narrowing that follows anterior thickening (n) 5.9

Width of pharynx at its middle length (m) 4.7

Width of posterior pharynx thickening (p) 9.9

Length of cephalic cilia 14.1–20.0 Hypostomium length 2.8

Cephalion length 9.3

Cephalion width 6.4

Diameter of mouth ring 4.7

Furca length 24.5

Length of adhesive tube 13.4

Neck spine length 8.3–10.0 Trunk spine length 10.4–17.1 Length of spine posterior body part 25.7

Length of posteriormost pair lateral spine 14.4

Neck scale length 2.5–4.8 Neck scale width 2.0–3.1 Trunk scale length 5.1–7.0 Trunk scale width 3.6–4.6 Sensory anterior bristles length?

Sensory posterior bristles length 12.4

Number of cephalic cilia in one tuft 3 (anterior); 4 (posterior) Number of separated cephalic tufts 4

Number of scales in single longitudinal row 26

Total number of longitudinal alternating rows of scales 18

Pharynx formula a 31.1

Pharynx formula n 15.5

Pharynx formula m 19.3

Pharynx formula p 32.5

Ratio of scale distribution 69.2

Length ratio of terminal spines 10.5

C. (P.) acanthodes Stokes, 1887 (124–159 Μm in length) has a different body shape and proportions. Other differences are the scale shape and scale arrangement. C. (P.) acanthodes dorsal scales are rounded, without posterior notches and the scales are arranged in 20 longitudinal alternating rows of scales and 20–24 scales in each row, unlike in C. (C.) sp. 2. Also, the shape of the furca and adhesive tubes is clearly different. C. (P.) acanthodes has a furca that is parted distinctly outwards, and straight adhesive tubes. The greatest similarity in both compared species is the presence of a line of a long trunk spines without lateral denticles. However, in the compared species the long spines are considerably shorter (10–17 Μm) than in the C. (C.) sp. 2 and are located in the middle part of the trunk. Moreover, in C. (P.) acanthodes 5 tranverse row of spines occur that are considerably longer than the neighbouring spines (2 lines behind the pleurs, 1 line in the middle trunk part and 2 lines in the posterior body part), unlike in C. (C.) sp. 2, which has only one line of considerably longer spines.

C. (P.) macrolepidotus macrolepidotus Greuter, 1917 (143–151 Μm in length) is a larger species. It resembles C. (C.) sp. 2 in body shape and proportions. Moreover, the distribution of the length of spines is the same. In C. (P.) m. macrolepidotus the spines on the longer lines from the lateral body sites are of different length (23 Μm) than the line spines in the trunk site (18 Μm). Also, the furca shape is exactly the same, but it is shorter (18 Μm). The most important differences between these species are scale shape and scale arrangement. In C. (P.) m. macrolepidotus large, rounded scales occur without posterior notches. Also, in C. (P.) m. macrolepidotus the scales begin on the neck, in contrast to the discussed species, in which scales begin directly after the cephalic plates.

C. (C.) sphagnophilum Kisielewski, 1981 (122–148 Μm in length) has a slender body shape and different body proportions. Also, the length of spines is definitely shorter (neck: 3–9 Μm; trunk: 7–13 Μm) and not as varied as in C. (C.) sp. 2. Moreover, scale shape in both compared species is similar, although in this species the scales are one– lobed instead of three–lobed. Additionally scales distribution is also different (12–19 longitudinal alternating rows of scales, 21–26 scales in each row).