Chaetonotus (Hystricochaetonotus)

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 : 265-266

Chaetonotus (Hystricochaetonotus) sp. 3 ( Table 12)

Locality: Site: 2; session I, II.

Material: 2 samples, 3 specimens (only adults), 2 specimens photographed. Short description: The body is widest in the middle of the trunk. It has a circular clearly five–lobed head, which is separated from the wider part of the trunk by a distinct narrowing of the neck. The species has a narrow cephalion, epipleuria and hypopleuria visible in the head outline. The hypostomium is narrow and rectangular in shape, with no transverse cuticular bars. On the head there are two pairs of cephalic ciliary tufts. The mouth ring is located terminally. The pharynx has a dilatation at anterior and posterior ends. The furca is slightly spaced apart outward. The species has straight thin adhesive tubes. The anterior and posterior sensory bristles are anchored at rounded double–keeled scales. The body, except for the ventral interciliary fields, is covered with one–lobed scales having distinct keels and spines. The scales have rounded anterior edges and shallow posterior notches, and they are placed close to each other in 14 alternating longitudinal rows, 16–18 scales in each row. The spines are thin and curved, without lateral denticles. In the middle part of the trunk there are 7 long and thick spines, also without lateral denticles and bifurcated ends. The spines form 2 rows, with 3 spines in the anterior and 4 spines in the posterior row. The rearmost pair of lateral spines is longer and thicker than the trunk spines (except the 7 long spines in the middle part of the trunk). The ventral interciliary field is almost naked as it only has two terminal scales. The ventral terminal scales are small, elongated, and oval in shape, with weak keels and long straight spines without lateral denticles. Ocellar granules are absent.

Differential diagnosis: C. (H.) sp. 3 is most similar to Chaetonotus (Hystricochaetonotus) acanthophorus Stokes, 1887 , Chaetontus ( Hystricochaetonotus ) balsamoae Kisielewski, 1997 (b), Chaetonotus (Hystricochaetonotus) quintospinosus Greuter, 1917 , and Chaetonotus (Hystricochaetonotus) spinulosus Stokes, 1887 .

C. (H.) acanthophorus Stokes, 1887 (100–108 Μm in length) is a larger species. It has a different number and arrangement (4 rows, 5 in each) of the long trunk spines. Moreover, the lateral denticles on the longer dorsal spines are present, unlike in the C. (H.) sp. 3. An important similarity between the two species is the pair of posteriormost lateral spines. In these species this pair of spines is stronger and longer than the other trunk spines (except for the long dorsal spines), and there are no lateral denticles.

C. (H.) balsamoae Kisielewski, 1997 (147–172 Μm in length) is a larger species. Additionaly, the distribution (on the anterior trunk part), number (7–9) and arrangement of spines in 4 rows are entirely different from the discussed species. Furthermore, it has double lateral denticles on the long trunk spines, in contrast to C. (H.) sp. 3, which does not have any. Additionally, tips of adhesive tubes of the compared species are widely apart and the pair of the posteriormost lateral spines is of the same length and thickness as the other trunk spines (except for the long dorsal spines).

C. (H.) quintospinosus Greuter, 1917 (80– 102 Μm in length) has the body shape and covering significantly different. The species has only 5 scales with long spines, the remaining part of the body is not covered with any scales. Furthermore, the long dorsal spines possess lateral denticles.

C. (H.) spinulosus Stokes, 1887 (67–89 Μm in length) has 6 scales with long spines on the dorsal trunk, and the lateral body surface is covered with scales, while the remaining part of the body is naked. Furthermore, the number and distribution of spines of the posterior parts of the trunk do not correspond to C. (H.) sp. 3. In addition the presence of lateral denticles on the long spines and of short and thin rearmost lateral spines in C. (H.) spinulosus .

Distribution: It is a very common species with wide distribution in Europe. Its representatives have been found so far in such countries as Denmark (Grilli et al. 2010), France (d’Hondt 1967), Germany (e.g. Remane 1925), Great Britain (e.g. Martin 1981), Italy (e.g. Balsamo 1990), Poland (e.g. Kisielewska & Kisielewski 1986a, b, c), Romania (Rudescu 1967), Russia (Preobraženskaja 1926), Switzerland (Greuter 1917), and Sweden (Kånneby et al. 2009). The species occurs also in Brazil (Kisielewski 1991), Canada (Schwank 1990), Israel (Kisielewski 1999), and Korea (Lee & Chang 2000).