Chaetonotus (Chaetonotus) pravus, Kolicka, Małgorzata, Kisielewski, Jacek, Nesteruk, Teresa & Zawierucha, Krzysztof, 2013

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 : 252-258

Chaetonotus (Chaetonotus) pravus sp. nov. ( Figs 18–23 ; Table 7 )

Locality: Site 2; session I, II.

Material: 2 samples, 2 specimens found directly in the sample as well as 25 specimens from the laboratory culture (with 1 juvenile). All specimens photographed. The photographs of holotype and three paratype are available in Natural History Collection at Adam Mickiewicz University in Poznań under accesion number NHC- GCCP-3-1-6/h (holotype) and NHC-GCCP- 3-7-33 /p (paratypes). Additional all photographs are available at Adam Mickiewicz University in Poznań, in the collection of the first author.

Etymology: From Latin pravus —perverse, which points to the unique distribution of the three pairs of very long spines of the furca base and the two different types of dorsal scales.

Diagnosis: Body length from 92.3 to 111.7 Μm. Body slender with pronounced neck constriction. Head clearly five–lobed, parabolic in shape. Epipleuria separated by distinct indentations of the cephalion and hypopleuria. Hypopleuria approximately twice as large as epipleuria. All plates well visible in the head outline. Kidney–shaped hypostomium. Two pairs of cephalic ciliary tufts, 6.7 to 28.8 Μm in length. Mouth ring 4.4–5.4 Μm in diameter located subterminally. Pharynx of length 24.4–29.2 Μm, with dilatations at both ends. Furca 15.5–17.8 Μm long, pointing outwards. Straight, blunt adhesive tubes are wide apart and from 8.0 to 9.2 Μm in length. The body, except for the interciliary field, is covered with two types of one–lobed scales with distinct keels and spines arranged in 22–26 longitudinal alternating rows and 20–26 scales in each row. Scales spaced wide apart. The first type of scales is situated in longitudinal rows lying behind the cephalion and epipleuria. These scales are short and wide with deep posterior notches, have a triangular shape with rounded sides and short, slightly curved spines without lateral denticles. The second type of scale is situated longitudinally on the dorsal and ventrolateral sides. These scales are long and narrow, with a sharp triangular shape and deep posterior notches. The spines arising from this type of scales are slightly curved and without lateral denticles. Longer and more strongly curved spines arise laterally from one column consisting of scales of the second type. Three pairs of the posteriormost lateral spines are very long and greatly curved. The terminal pair of trunk spines is the longest and the thickest. On the furca base are three pairs of long, curved spines, of which the terminal pair extends beyond the adhesive tubes. The ventral interciliary field is covered with relatively large circular scales without keels and spines. Two pairs of large ventral terminal scales. Anterior pair is elliptical in shape with rounded notches in the upper part of the scales, with keels. The posterior pair is rectangular in shape, without keels and with straight spines. Ocellar granules absent.

Description: Chaetonotus (Chaetonotus) pravus sp. nov. is a small species with a slender body. The head gradually turns into a thinner neck. The head is parabolic in shape, clearly five–lobed with a separated cephalion (U1–U5), and two pairs of pleurs (U3–U12). All of the cephalic plates are well visible in the head outline. The epipleuria are separated from the cephalion and from the hypopleuria by a deep indentation. The hypopleuria are approximately twice as large as the epipleuria and are located at U6–U12. On the head are two pairs of cephalic ciliary tufts containing three cilia each. The anterior pair of tufts has cilia that are shorter than the posterior pair. Ocellar granules are absent. The mouth ring is situated subterminally at U2–U5. In the mouth ring construction reinforcements typical of the genus Chaetonotus are present. Below the mouth is a kidney–shaped hypostomium is located. Near the posterior hypostomium edge there is a slight transverse bar. The neck is narrower than the head, and it gradually turns into the trunk (U29–U86). The trunk gradually expands to ca. U45 and subsequently, gradually and slightly tapers from U69 to the furca base. The furca base is distinct and massive, situated at U86. The furca branches arranged unparallel, tips of adhesive tubes widely apart to the body width at the widest point ( Fig. 21 ). Straight, blunt adhesive tubes (U93–U100) have the same thickness along the entire length ( Fig. 22 A). On the dorsal and ventrolateral sides are two types of one–lobed scales with distinct keels and spines, without lateral denticles ( Fig. 19 ). The scales are arranged in 22–26 alternating longitudinal rows, 20–26 scales in each row. In the central part of the trunk, in longitudinal rows lying behind the cephalion and epipleuria, are short and wide scales with short, almost straight spines ( Fig. 22 B). These scales are triangular in shape, with rounded sides. In the longitudinal rows behind the hypopleuria, on the sides of the body, and on the ventrolateral side, are long and narrow scales of a sharp triangular shape with deep posterior notches. Slightly curved spines arise from these scales. On both sides of the body from one column of narrow and long scales arise spines of greater length that are strongly curved. The scales adjacent to the longitudinal ciliary bands are turned by ca. 45º towards the locomotor band. The scales are arranged in large distances from one another, with the spacing between the scales being similar to the scale size. The length and width of the scales slightly and gradually increases from the head, through the neck to the widest trunk part and subsequently gradually decreases to the furca base. The exceptions are three pairs of the rearmost longitudinal spines which are considerably longer than the other spines and are strongly curved and thicker. The terminal pair of the trunk spines is the longest, the thickest and up to U97. A very important feature is the presence of three pairs of lateral spines on the furca base ( Fig. 20 ; 22 A). They are long and curved. The terminal pair arises from the scales; it is situated at the furca base and extends beyond the adhesive tube end. Two pairs of dorsal sensory bristles anchored at the double–keeled scales are present. The anterior pair of the double–keeled scales is located at U27–U28, the posterior double–keeled scales are located at U72–U73.

On the ventral surface longitudinal ciliary bands start at U5 and end at U84. The interciliary field (U10–U84) is covered with relatively large, one–lobed scales arranged alternately and at large distances from one another. The scales are circular in shape and do not have keels or spines. There are two pairs of ventral terminal scales. The anterior pair of scales is located at U82–U85. They are of an elliptical shape with rounded notches from the top edges of the scales. These scales have a keel extending from the anterior scale edges; spines are absent. The posterior pair of scales in the ventral interciliary field is located at U84–U89. They are rectangular, without keels, and with straight spines reaching beyond the furca indentation.

Character N Holotype Ranges on adult SD N Ranges on juvenile SD

specimens specimens

Body length 24 99.0 92.3–111.7 4.77 2 87.3–97.1 6.93 Pharynx length 23 24.7 24.4–29.2 1.07 2 24.5–27.2 1.91 A—Dorsal view, B—View of internal morphology, C—Ventral view. All measurements in micrometers.

The pharynx (U3–U27) has a well–developed anterior dilatation (U5–U27) and a posterior dilatation (U23– U27) of a larger width than the anterior one. The pharynx is connected via the pharyngeal intestinal junction (U28) to the straight intestine without a separated enzymatic section (U28–U86).

Taxonomic remarks: Specimens from the laboratory culture are marginally larger than the adult individuals (holotype) found in the Poznań Palm House. This may be explained by different growth conditions (e.g. mainly by lack of predators).

Differential diagnosis: Chaetonotus (Chaetonotus) pravus sp. nov. shows a specific distribution of spines at the furca base and two different kinds of scales, not found previously in any other species. From all the hitherto known taxa, the new species is most similar to Chaetonotus (Hystricochaetonotus) hystrix Mečnikow, 1865 , and Chaetonotus (Chaetonotus) sphagnophilus Kisielewski 1981 . In both of the compared species, the body, excluding the ventral interciliary fields, is covered with one type of scale and only one pair of sensory bristles (the posterior one) is present, unlike C. (C.) pravus sp. nov., which has two different types of body scales. Also, in the new species, in one longitudinal row on both sides of the body, the spines are longer than the other spines, which do not occur in C. (H.) hystrix and C. (C.) sphagnophilus .

A—Adult specimen—holotyp, B—Juvenile specimen. All measurements in micrometers.

C. (H.) hystrix Mečnikow, 1865 (87–130 Μm in length) has well separated and wider head than in the new species, and the furca shape is different as well ("V"-shaped furca not as in the new species parabolic shape furca).

Moreover, C. (H.) hystrix has scales of a different type (three–lobed, not one–lobed) and different distribution (11– 13 longitudinal alternating rows of scales, 12–13 scales in each row). Furthermore, this species has longer spines with lateral denticles (neck: ca. 4.5 Μm; trunk: 10–13 Μm) and does not have spines at the furca base, in contrast to the newly described species.

C. (C.) sphagnophilus Kisielewski, 1981 (122–148 Μm in length) is a larger species. However, its head is shorter and the furca base is less massive. The spines in this species are longer (neck: 3–6 Μm; trunk: 5–9 Μm) and have a different shape and distribution (12–19 longitudinal alternating rows of scales, 21–26 scales in each row). An important difference between both compared species is the different number of spines present at the furca base. In C. (C.) sphagnophilus there is one pair of spines that is laterally situated, instead of three as in the new species. In this species the length and thickness of the rearmost pair of lateral spines is similar to the other trunk spines (7– 13 Μm vs 4–12 Μm), unlike in C. (C.) pravus sp. nov., in which the last pair of trunk spines is definitely longer and thicker. Also, the rearmost pair of lateral spines located at the base of the adhesive tubes is longer than the common trunk spines (11.1–16.3 Μm).

A—Dorsolateral view, B—View of internal morphology, C—Ventral view. All measurements in micrometers.

A—Ventral body side, B—Dorsal view of scales in trunk region. All measurements in micrometers.

Figures

FIGURE 18. Chaetonotus (Chaetonotus) pravus sp. nov.

FIGURE 19. Chaetonotus (Chaetonotus) pravus sp. nov. — two types of dorsal scales A—Narrower scale, B—Wider scale. All measurements in micrometers.

FIGURE 20. Chaetonotus (Chaetonotus) pravus sp. nov.

FIGURE 21. Chaetonotus (Chaetonotus) pravus sp. nov.

FIGURE 22. Chaetonotus (Chaetonotus) pravus sp. nov.

FIGURE 23. Chaetonotus (Chaetonotus) pravus sp. nov. — paratype with mature egg

Tables

TABLE 7. Morphometric parameters for Chaetonotus (Chaetonotus) pravus sp. nov.; N—number of specimens or structures analysed, Range—the smallest and the largest structure found among all specimens measured, SD— standard deviation.

Width of anterior pharynx thickening (a) Width of pharynx narrowing that follows anterior thickening (n) Width of pharynx at its middle lengt (m) Width of posterior pharynx thickening (p) Length of cephalic cilia	19 18 19 19 24	7.2 7.2–8.7 0.42 4.8 4.7–6.7 0.48 6.0 5.7–7.3 0.61 9.2 8.3–10.3 0.49 10.1–19.2 (6.7–11.3)–(10.0–20.8) 1.07–2.33	1 1 1 1 2	6.4 4.2 5.4 8.0 (8.6–8.9)–(19.0–19.6)	– – – – 0.21–0.42
Hypostomium length	22	4.8 4.1–5.5 0.35	2	4.3–4.7	0.28
Cephalion length	23	4.8 4.8–6.4 0.48	2	4.2–6.0	1.27
Cephalion width	23	9.3 8.8–10.9 0.57	2	7.2–10.2	2.12
Diameter of mouth ring	25	4.9 4.4–5.4 2.92	2	4.6–4.9	0.21
Furca length	25	15.8 15.5–17.8 0.83	2	15.3	0.00
Length of adhesive tube	25	8.2 8.0–9.2 0.35	2	8.1–8.7	0.42
Lateral neck spine length	24	3.1–3.6 (2.7–3.5)–(3.6–4.6) 0.20–0.25	2	(3.0–3.2)–(4.2–4.5)	0.14–0.21
Lateral trunk spine length	24	3.6–5.7 (3.6–5.0)–(5.1–6.7) 0.31–0.54	2	(4.4–4.5)–(5.8–6.8)	0.07–0.71
Neck spine length	22	2.0–2.6 (1.6–2.2)–(2.2–2.9) 0.17–0.21	1	1.9–2.7	–
Trunk spine length	22	2.7–3.5 (2.3–3.0)–(3.2–4.3) 0.20–0.38	1	2.8–3.1	–
Length of last pair trunk spines	22	16.8 12.6–19.5 1.89	2	15.8–16.7	0.64
Length of posteriormost lateral pair of spines on the furca base Narrower neck scale length	22 21	11.7 11.1–16.3 1.59 2.5–3.0 (2.1–3.3)–(2.9–4.1) 0.29–0.39	2 1	11.3–11.6 2.1–2.7	0.21 –
Narrower neck scale width	21	1.1–1.7 (1.1–1.6)–(16–2.5) 0.15–0.23	1	1.2–1.6	–
Wider neck scale length	22	2.2–2.9 (1.6–2.3)–(2.5–3.3) 0.18–0.28	1	1.9–2.7	–
Wider neck scale width	22	1.6–2.2 (1.4–2.0)–(1.9–3.2) 0.16–0.32	1	1.5–2.1	–
Narrower trunk scale length	21	3.1–4.4 (3.1–4.3)–(4.2–5.9) 0.38–0.47	1	3.1–4.0	–
Narrower trunk scale width	21	1.7–1.9 (1.6–2.9)–(1.9–3.6) 0.29–0.40	1	1.7–1.9	–
Wider trunk scale length	21	3.1–4.1 (2.2–3.8)–(3.4–4.8) 0.34–0.36	1	2.8–3.2	–
Wider trunk scale width	21	2.4–3.5 (2.0–3.2)–(2.5–4.0) 0.32–0.40	1	2.2–2.6	–
Anterior sensory bristles length	14	9.6 9.3–13.4 1.44	1	8.4	–
Posterior sensory bristles length	17	10.7 9.2–15.3 1.82	1	9.2	–
Size matured egg	1	– 38.8 x 20.5 –	2	–	–
Number of cephalic cilia in one tuft Number of separated cephalic tufts	27 27	3 (anterior); 3 (anterior); 0.00 3 (posterior) 3 (posterior) 4 4 0.00	2 2	3 (anterior); 3 (posterior) 4	0.00 0.00
Number of scales in single longitudinal row Total number of longitudinal alternating rows of scales Pharynx formula a	27 27 18	20 20–26 1.58 24 22–26 1.32 29.1 27.4–32.4 0.02	2 2 1	20 22–24 26.1	0.00 1.41 –
Pharynx formula n	18	19.4 18.7–23.9 0.02	1	17.1	–
Pharynx formula m	18	24.3 21.6–27.9 0.02	1	22.0	–
Pharynx formula p	18	37.2 33.9–37.8 0.02	1	32.6	–
Ratio of scale distribution	27	120.0 92.3–130.0 0.09	2	110.0–120.0	0.07
Length ratio of terminal spines	22	11.8 10.0–15.6 0.01	2	11.9–12.9	0.01