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 : 258-260

Chaetonotus (Chaetonotus) sp. 1 ( Table 8)

Locality: Site 1; session II.

Material: 1 sample, 1 adult specimen, photographed.

Short description: This species is relatively large, with a slender body, and the head separated from the trunk by a neck constriction. The trunk in the widest section is slightly wider than the head. It also has a rounded five– lobed head with cephalion, epipleuria, and hypopleuria separated by weak indentations, visible in the head outline. The hypopleuria are slightly longer than the epipleuria. The hypostomium is elliptical and with a small transverse cuticular bar near the anterior edge. On the head there are two pairs of cephalic ciliary tufts with three cilia in the anterior and five cilia in the posterior tuft. The mouth ring is located subterminally. The pharynx has two distinct dilatations at the ends. Intestinal enzymatic section present. The V–shaped furca is spaced externally with straight adhesive tubes (tips of adhesive tubes widely apart). The dorsal sensory bristles are absent. The whole body, except for the ventral interciliary field, is covered with one–lobed scales, with distinct keels and spines. The scales are situated close to each other in 42 alternating longitudinal rows, 49 scales in each row. They have rounded anterior edges and elliptical notches at the posterior edges. The spines are long, thin, strongly curved, and without lateral denticles. The length of the spines gradually increases towards furca base. The posteriormost pair of lateral spines is the longest and thickest and they reach beyond the ends of the adhesive tubes. The ventral interciliary field is covered with two types of scales. In the pharyngeal section there are small circular scales without keels and spines. In the intestine section there are rounded rectangular scales with straight spines. The middle pair of terminal scales is elongated and more oval, with keels and long straight spines without lateral denticles. The two other pairs of terminal scales have slight keels. Ocellar granules are absent.

Differential diagnosis: C. (C.) sp. 1 is similar to Chaetonotus (Chaetonotus) brevispinosus Greuter, 1917 , C haetonotus ( Chaetonotus ) greuteri Reamne, 1927, and Chaetonotus (Chaetonotus) maximus Ehrenberg, 1830 . An important feature is that all of the compared species have dorsal sensory bristles, in contrast to C. (C.) sp. 2.

C. (C.) brevispinosus Greuter, 1917 (90–160 Μm in length) is a smaller species. The shape of the scales is similar to scales observed in C. (C.) sp. 1, although they lack keels. However, scale distribution in this species is different (27–33 longitudinal alternating rows of scales, 21–30 scales in each row). Additionally, C. (C.) brevispinosus has a short (22–33 Μm in length) and very wide pharynx (formula a: 37–39%; m: 29–36%; p: 39–47%). In this species the trunk spines are considerably shorter (3–7 Μm) and their length does not increase gradually to the posterior body end. Also, the pair of the posteriormost lateral spines is considerably shorter (5–12 Μm).

A—Lateral view; B—Dorsal view; C—Ventral view. All measurements in micrometers.

C. (C.) greuteri Reamne, 1927 (150–208 Μm in length) has an entirely different body shape and proportions. Moreover, scale shape (triangular scales) and distribution in this species is different (23–27 scales in single longitudinal row and 19–27 longitudinal alternating rows of scales) (Kisielewski 1999). Aditionally, C. (C.) greuteri has a substantially shorter pharynx (30–38 Μm in length) (Kisielewski 1999).

C. (C.) maximus Ehrenberg, 1830 (from 112–330 Μm in length) has the pair of the posteriormost lateral spines considerably shorter (12–14 Μm). Also, the covering of the dorsal and ventral body surfaces is different. On the dorsal side of C. (C.) maximus scales are arranged in 17–21 longitudinal alternating rows with 21 scales in each row, which constitutes a much lower number of scales than in the discussed species. In the pharyngeal section of the interciliary field, the scales turn into transverse plates, unlike the new species.

Character Specimen Body length 178.6 Pharynx length 50.1

Width of anterior pharynx thickening (a) 14.4

Width of pharynx narrowing that follows anterior thickening (n) 11.6

Width of pharynx at its middle length (m) 12.3

Width of posterior pharynx thickening (p) 18.7

Length of cephalic cilia 21.6–35.4 Hypostomium length 5.8

Cephalion length 9.5

Cephalion width 20.7

Diameter of mouth ring 7.6

Furca length 21.5

Length of adhesive tube 10.9

Neck spine length 9.3–10.2 Trunk spine length 10.5–13.6 Length of spine posterior body part 14.6–22.4 Length of posteriormost paire lateral spine 23.0

Neck scale length 2.4–3.2 Neck scale width 1.8–2.6 Trunk scale length 3.4–4.8 Trunk scale width 2.6–3.4 Number of cephalic cilia in one tuft 3 (anterior); 5 (posterior) Number of separated cephalic tufts 4

Number of scale in longitudinal row 49

Totall number of longitudinal alternatin rows of scale 42

Pharynx formula a 28.7

Pharynx formula n 23.2

Pharynx formula m 24.6

Pharynx formula p 37.3

Ratio of scale distribution 85.7

Length ratio of terminal spines 12.9