Chaetonotus (Hystricochaetonotus) horridus Kolicka 2019, sp. nov.
Creators: name: Kolicka, Małgorzata
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Gastrotricha
Chaetonotida
Chaetonotidae
Chaetonotus

description: Chaetonotus (Hystricochaetonotus) horridus sp. nov.
urn:lsid:zoobank.org:act: 478175BF-E4D8-48BC-AE73-2032127AB69D
Figs 16–25, A 3–A 6; Tables 4, A 3–A 4
Diagnosis
Stocky body, measuring from 107.8 to 134.0 μm in length. Head five-lobed, cephalion narrow, hypopleurae slightly larger in size than epipleurae. All cephalic plates weakly demarcated in head outline. Hypostomium small, rectangular in shape. Ocellar granules absent.Almost all scales three-lobed and keeled. Scales distributed in 15–21 total longitudinal rows (3D +2–4DL+4–6L+4LV+2– 4V), with 13–15 scales in central row. Scales strongly differ morphologically in various body areas. On dorsal trunk area, large scales with very long, thick spines with a strong, very prominent lateral denticle. Two pairs of posteriormost trunk lateral scales with long, thick spines with strong lateral denticle. Remaining scales with simple, shorter and thinner spines or on central dorsal trunk area and on furcal appendages with rudimentary spines or without spines. Parafurcal spines absent. Spines on ventral surface hair-like, with narrow, delicate lamellae along entire length. Entire ventral interciliary field covered with plate-like scales. Three pairs of ventral interciliary field terminal scales. Pharynx wide, with pronounced anterior and posterior dilatations. Intestine straight without anterior section differing in form and morphology.
Etymology
From the Latin ʻ horridus ʼ = ʻhairyʼ, referring to the very long and strong trunk spines.
Material examined
Holotype POLAND • adult; Kraków, Botanical Garden, Jubilee Greenhouse, site 1; 50°03'38" N, 19°57'30" E; 15 Nov. 2013; M. Kolicka leg.; NHC-GCHH-22-1-25/h (photomicrographs, also in the author's collection).
Paratypes POLAND • 80 adults, 30 subadults, 9 juveniles; same locality as holotype; sites 1–3; 15 Nov. 2013 and 17 Apr. 2014; M. Kolicka leg.; NHC-GCHH-22-21-60/p (photomicrographs, also in the author's collection).
Description
HABITUS. Chaetonotus (Hystricochaetonotus) horridus sp. nov. has a stocky body that is slightly bottleshaped (Figs 16, 19). Its head is only slightly wider than the neck and the neck constriction is weakly demarcated. The neck gradually tapers from the head (from U17) to the beginning of the trunk (ca U31). The trunk is slightly wider than the head and gradually dilates from ca U32 to ca U59, where it is at its maximum width. Then it gradually tapers towards the narrow furcal base (from U79) (Figs 16, 19). The furcal base is clearly demarcated and narrow. The furcal indentation is V-shaped. The furcal branches are set widely apart and point outwards to the widest trunk region (Figs 16, 19). The adhesive tubes are straight, fairly thick and slightly tapered towards the blunt ends (Figs 16, 19).
HEAD. The head is five-lobed, short and semicircular in shape. The cephalion (U1–U4) is narrow, short, with straight dorsal edge. It adheres to the head along its entire length and rapidly extends near the dorsal edge (Fig. 20A). The epipleurae (U4–U7) are slightly arched and weakly demarcated in the head outline. They are located on the dorsal, dorsolateral and lateral sides and are slightly visible on the ventrolateral head side. The hypopleurae (U8–U14) are slightly larger in size than the epipleurae and located entirely on the ventrolateral and ventral head sides (Figs 16, 20 A–B). They are not visible in dorsal body view. On the dorsal head surface, between the lateral edges of the cephalion and epipleurae there is a prominent space, their edges meeting only in the cephalion extension place. Deep notches are present between the cephalion and epipleurae and between the epipleurae and hypopleurae. The hypostomium (U6–U7) is short, rectangular, with a slightly reinforced anterior edge (Figs 16C, 20B). Two pairs of cephalic ciliary tufts are present. The anterior tufts emerge in the area between the cephalion and epipleurae on the dorso-terminal head surface (ca U3) and consist of 5 cilia. The anteriormost cephalic cilium is very short and the length of the cilia in the anterior tuft gradually increases from the anteriormost to the fourth cilium. The fourth cilium in the anterior tufts is very long, the longest in both pairs of tufts, while the fifth, posteriormost cilium is much shorter. The posterior tufts (at U6–U7) have 4 cilia each and emerge on the ventral head side, above the anterior edge of the hypopleurae. The length of the cilia in the posterior tuft gradually increases from the anteriormost to the fourth cilium. Ocellar granules are not present. The mouth ring is large, wide and located subterminally at U2–U5. It has very strong, long reinforcements and long inner hairs (Figs 16C, 20B). Suboral bristles are located in two tufts located beneath and laterally to the mouth ring and reaching beyond the hypostomium end (between U3 and U7).
SCALES. The entire body, except for one pair of scales on the furcal appendages, is covered with threelobed scales that adhere to the cuticle along their entire surface (Fig. A6). All scales have a strong keel and are shaped like triangles. The scales are distributed in 15–21 total longitudinal alternating rows (3D +2–4DL+4–6L+4LV+2– 4V), with 13–15 scales in the central row. The central longitudinal rows of scales begin on the head directly beneath the posterior edge of the cephalion. On the head and anterior neck region the scales are located far from one another, on the posterior neck and anterior trunk region the scales are located gradually closer, but still at a distance to the other scales and not juxtaposed. The dorsolateral, lateral, ventrolateral and ventral trunk scales are located at a distance from the other scales, whereas the dorsal trunk scales and scales on the furcal appendages have slightly overlapping posterolateral edges (Fig. 20). The head anteriormost scales are situated near the posterior edge of the cephalion and epipleurae. The dorsal anterior scales are located aslant, whereas the dorsolateral scales are arranged parallel to the longitudinal body axis. These scales are elongated and their central lobes are long, trilobed and have very long keels. Their posterolateral lobes are slightly separated, narrow, slanted downward and create a narrow, deep V-shaped posterior scale notch (scale 1; Fig. 17A). The remaining scales of the head are significantly wider. The central lobes of these scales become shorter and simultaneously the posterolateral lobes become slightly longer, whereas their keels are shorter. The posterolateral lobes are directed diagonally downward and laterally; they create a deep and wide posterior scale notch (scale 2; Fig. 17B). The anterior neck scales become gradually longer than the head scales. Their central lobes become longer and the posterolateral lobes are more separated and directed more downward and create a wide and deep V-shaped posterior scale notch (scale 5; Fig. 17E). From the neck towards the trunk, the scale size gradually increases (from 2.8–3.5 ×2.4–3.2 to 5.2–6.4 ×5.1–5.9 μm). All of the anterior trunk scales and dorsolateral, lateral, ventrolateral and ventral trunk scales on the central and posterior body region have a wide and rounded anterior central lobe and clear, separate, long, narrow and sharp posterolateral lobes. The posterolateral lobes are directed diagonally downward and are slightly lateral; they create a deep V-shaped posterior scale notch (scale 8; Fig. 17H). The size of these scales increases from the anterior trunk region to the widest body region (from 3.0–4.1 ×2.1–3.3 to 5.6–9.7×4.68–8.43 μm) (Figs 20, 23). Dorsally and dorsolaterally from ca U37 to U73 and dorsally to U81, larger and thick, different scales are located with very long and strong spines (Figs 16, 20, 22). The first of the different, larger scales from each longitudinal dorsal and dorsolateral row are triangular in shape, their central lobes are short, wide and pass seamlessly into posterolateral lobes that are directed very wide apart. The posterior edge of this scale is almost straight and only very narrowly notched. Its keel starts from the half-length of the central lobe and is very pronounced and high, strongly triangular in shape (scale 11; Fig. 17K). The subsequent large scales (located from U41 to U73) are triangular in shape, with rounded edges, and their central lobes are longer and have longer keels. The posterolateral lobes of these scales are more rounded, directed slightly more downward and create a wide V-shaped posterior scale notch (scale 12; Fig. 17L). The posteriormost scale of the dorsal and dorsolateral large scales with long, strong spines is located in the central longitudinal row of scales at U78 to U81 (Figs 17A, 19A, 22B). This scale is wide and its central and posterolateral lobes are rounded. The posterior edge of this scale is almost straight and only very narrowly notched. Its keel is very pronounced and high, strongly triangular in shape (scale 13; Fig. 17M). Anteriorly to the double keeled scales with trunk dorsal sensory bristles, on the dorsal and dorsolateral trunk region, three pairs of keeled and spineless scales are located at U73–U77. Two of these three pairs are located more anteriorly and laterally than the third pair and are triangular in shape, their posterolateral lobes are weakly separated, and their keels are strong and reach from the anterior part of the central lobes to the ends of the posterolateral lobes. The posterior notches of these scales are shallow and semicircular (scale 14; Fig. 17N). The third pair of these scales, located at U75–U77, is wider and possesses shallower posterior notches (scale 15; Fig. 17O). On the lateral surface of the posterior trunk region, one pair of the second to last trunk scales is located at U69–U75. These scales are large and have a long, wide, and anteriorly clearly pointed central lobes with strongly rounded lateral edges. Their posterolateral lobes are clearly separated from the central lobes, are long and have sharp edges. These posterolateral lobes are directed diagonally downward (scale 16; Fig. 17P). The scales have strong keels and strong, long spines. Posteriorly to them, on the posterior trunk region and furcal base, the last pair of trunk lateral scales is situated at U76–U82. This pair of scales is large (7.4–11.7 ×5.3–8.9 μm); its scales have a long, wide and anteriorly strongly pointed central lobes and straight posterolateral lobes that are triangular. The posterolateral lobes of these scales are directed diagonally wide apart, downward and laterally, creating a wide and shallow V-shaped posterior scale notch. These scales have a very strong keel and strong, long spines (scale 17; Fig. 17Q). One pair of small (2.2–7.0 ×1.6–4.5 μm) three-lobed scales, shaped like triangles with strongly rounded anterior lobes and with straight, narrow and long posterolateral lobes, is located diagonally on the dorsal surface of the furcal base (at U81–U83). These scales have long, thin keels and are spineless. Their posterior edge notches are V-shaped and very deep (scale 18; Fig. 17R). Two pairs of three-lobed, elongated and narrow scales are located on the dorsal surface of the furcal base and furcal appendages (at U82–U86). These scales have wide and rounded central lobes and straight, narrow posterolateral lobes located diagonally downward which create narrow, deep V-shaped posterior scale notches. Their keels are long and thin and the scales are spineless (Fig. 22B). The scales are diagonally arranged and directed towards the central body axis (scale 19; Fig. 17S). One pair of slightly three-lobed, narrow, asymmetrical scales is located on the dorsal surface of the furcal appendages. These scales are shaped like strongly elongated ovals, with a slightly triangular posterior notch. This pair of scales has long keels running along their length and does not have a spine (scale 20; Fig. 17T). They are located at U86–U88, slightly diagonally to the central body axis. Dorsolaterally at the furcal appendages, one pair of scales with two keels is located (at U86–U89). These scales are oval in shape and do not have any posterior notches or spines. Their keels are long and slightly bent (scale 21; Fig. 17U). The edges of the furcal appendage scales are slightly overlapping (Fig. 22). The size of the scales gradually decreases slightly from the dorsal, dorsolateral, lateral, ventrolateral and ventral surfaces towards the ciliary bands (head: from 3.2–5.2 × 3.2–6.2 to 2.2–4.1 × 2.1–3.9 μm; neck: from 4.5–6.4 ×4.1–5.9 to 2.8–4.6×2.4–4.1 μm, trunk: from 5.3–9.7 ×4.1–8.4 to 3.0–5.5 ×2.1–4.6 μm) (Table A3). Furthermore, the edges of the dorsolateral, lateral, ventrolateral and ventral scales gradually become slightly more rounded towards the ciliary bands as compared to the edges of the dorsal scales (Figs 16, 20). Scales arranged in the ventral longitudinal row located closest to the ciliary bands are smaller than the scales of the other rows, and their anterior edge is oriented towards the bands at an angle of ca 20°.
SPINES. In this species, five main types of spines may be distinguished (Fig. 18). The first type of spine bends slightly along its entire length and tapers towards the end, without lateral denticles. This type of spine emerges from the anteriormost head dorsal scales (Fig. 18A). The second type of spine is basally bent, tapering towards their ends, with a weak lateral denticle. These spines emerge from the dorsal, dorsolateral, lateral and ventrolateral head, neck and anterior trunk region scales and laterally and ventrolaterally on the remaining scales of the trunk part (Fig. 18B). The length and thickness of the spines gradually increase from the head towards the widest body region (ca U59) (from 1.8–13.7 to 7.9–19.6 μm). Moreover, their length gradually increases towards the ventrolateral surface (head: from 0.4–5.6 to 0.7–6.1 μm; neck: from 2.5–8.3 to 3.4–10.1 μm; trunk: 5.0–11.1 to 5.7–17.0 μm) (Table A3). The third type of spine is very long and thick, straight, with a prominent, deeply notched lateral denticle. The spines emerge from large (scales 11, 12 and 13), thick dorsal and dorsolateral trunk scales (from ca U37 to ca U73), are the longest (18.9–35.5 μm) and thickest body spines and have the most prominent lateral denticle (Fig. 18C). From scales 13, located on the posterior trunk region (at U78–U81), arise the last long dorsal and dorsolateral long spines (Fig. 21). These spines are slightly shorter than the preceding long spines and their lateral denticle is less prominent (18.9–27.2 μm). The fourth type of spine is long, thick, slightly bent and with a clearly marked lateral denticle (Fig. 18D). This type of spine arises from the second to posteriormost trunk pair of lateral scales located at U69–U75 and from the posteriormost trunk pair of lateral scales located at U76–U82 (Fig. 22 A–B). The posteriormost pair of trunk spines is longer (13.9–20.1 μm) and thicker than the second to posteriormost pair of lateral spines (11.6–16.7 μm) (Table A3), and their lateral denticles are more prominent and deeply notched (Fig. 22 A–B). The fifth type are long (7.2–19.5 μm), thin, hair-like spines with narrow, delicate lamellae along their entire length. These spines arise on the ventral surface, from scales arranged in one pair of longitudinal rows located closest to the ciliary bands (Fig. 18E). The lamellae are the widest here, ca one-third of the length of the spine, and taper towards the end of the spines (Fig. 21B).
DORSAL SENSORY BRISTLES. This species has three pairs of dorsal sensory bristles (Fig. 16A). The first, anterior pair is located on the dorsal surface of the head at U5, beyond the dorsolateral cephalion edges, whereas the second pair of sensory bristles is located on the dorsal surface of the posterior neck region at U27. The first and the second pairs emerge from small, spherical papillae. The third, posterior pair of sensory bristles is located dorsally and dorsolaterally on the posterior trunk and emerges from the three-lobed, double-keeled scales at U76–U79. The keels of these scales are connected in the centre of the scales, and the scales are shaped like double, sharp triangles with long, narrow posterolateral lobes set very wide apart and a double, deep posterior notch (Figs 16A, 22B).
VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. On the ventral surface, the longitudinal ciliary bands begin at U8 and run back to U87 (Fig. 16C). On the head region (from ca U8 to ca U11) the ciliary bands are merged (Fig. 16C) and subsequently are divided into two separate bands arranged parallel to one another. The entire ventral interciliary field is covered by plate-like scales. They are distributed in 7 longitudinal rows with 14–23 scales in the central row (Figs 16C, 19C, 22D). The ventral interciliary field anterior scales are partially recessed on the cuticle and isolation from the cuticle increases towards the posterior body part. The anterior scales are rounded to inverted egg-shaped (scale 22; Figs 17V, 20B), and towards the posterior body region the scales become gradually larger and more elongated (scales 23–24; Fig. 17 W–X). The posterior ventral interciliary field region scales (at U73– U79) are elongated, oval in shape, and have straight and thin keels (Figs 20F, 22D). From the anterior to posterior body region, the distances between the scales decrease, and beyond half the trunk length the scales start to overlap (Fig. 20D, F). Three pairs of ventral interciliary field terminal scales are present. The first pair (at U79–U85) is elongated and rectangular, with rounded anterior edges (scale 25; Fig. 17Y). They have a long, narrow keel and a long, thin and straight spine extending beyond the internal furcal indentation. The second and third pairs (at U86–U89) are elongated and rectangular, with rounded anterior edges (scale 26; Fig. 17Z). These pairs have long, narrow keels and possess short, rudimentary spines that only slightly extend towards the posterior scale edge (Fig. 22D).
INTERNAL MORPHOLOGY. The pharynx (from U2 to U30) is wide and has distinct, marked, rounded anterior and posterior dilatations. The posterior dilatation is wider than the anterior one (Fig. 24A). The pharynx is connected through the pharyngeal–intestinal junction to a straight intestine, running from U30 to U84. The pharyngeal–intestinal junction is clearly demarcated, short and narrow (U31). The X-organ of this species (observed in five specimens) is located at U83–U86 near the terminal part of the intestine. It is bilobed, built from two extensions enveloped in a thin coat and connected by a thinner band located below the intestine, at the ventral side. The extensions and the thin coat and the cellular bridge connecting the extensions have a grain-like structure (Fig. 25C). The pair of sperm packets of this species are circular in shape and contain spermatozoids (8–16 per packet) in the form of a short rod. The pair is located at U60–U62 on both sides, juxtaposed to the intestine. When only a single sperm pocket is present, it is irregular in shape, less compact and contains 8–16 spermatozoids. Unpaired sperm pockets, when present, are located at U64–U66, very near the internal trunk wall (Fig. 25C).
Remarks
The total body length of juvenile specimens of Chaetonotus (Hystricochaetonotus) horridus sp. nov. varied from 88.8 to 122.9 μm; length of pharynx between 27.6 and 34.2 μm; length of intestine from 36.4 to 58.2 μm; there were 15–21 total longitudinal rows of scales (3D +2–4DL+4–6L+4LV+2– 4V), with 11–15 scales in the central row. Out of 69 adults, nine had a large, developing egg, one had a developing egg, an X-organ and a single sperm packet, one had an X-organ and a single sperm packet, whereas two others had an X-organ and two sperm packets and the next one only had a single sperm packet; one had large, crescent-like formations inside the integuments (Fig. 25B) and another had diffuse formations (in both case probably some kind of parasitic structures).
Differential diagnosis
Of all 32 species belonging to the subgenus Hystricochaetonotus Schwank, 1990, Chaetonotus (H.) horridus sp. nov. most closely resembles C. (H.) acanthophorus Stokes, 1888, C. (H.) balsamoae Kisielewski, 1997, C. (H.) euhystrix Schwank, 1990 and C. (H.) novenarius Greuter, 1917 (Table A4). Chaetonotus (H.) acanthophorus shares the following characters with C. (H.) horridus sp. nov.: long and strong spines on the dorsal and dorsolateral trunk surfaces; two strong and long anteriormost lateral trunk spines. Chaetonotus (H.) balsamoae and C. (H.) novenarius were selected for comparison with the new species due to their similarity in possessing very long and strong spines with strong, prominent lateral denticles on the dorsal trunk surface. Chaetonotus (H.) euhystrix was selected for comparison with the new species due to its similarity in possessing very long and strong spines with strong, prominent lateral denticles on the dorsal and dorsolateral trunk surfaces; a large mouth ring; a similar number of scales in the central longitudinal row of scales; and type of covering of the ventral interciliary field. Despite the fact that among all of the hitherto known species in this subgenus, those listed above have the highest number of common features with C. (H.) horridus sp. nov., they are significantly different from it – most strikingly by scale type and shape, spine length variation, as well as arrangements of the long trunk dorsal spines and lateral denticle type. In order to avoid any doubts in comparisons with the new species, only the original descriptions of these species and three of the most detailed papers with morphological data were used (Balsamo 1983; Schwank 1990; Kisielewski 1997a). Comparisons between the new species and the most morphologically similar taxa have been summarised in Table A4.
description: Published as part of Kolicka, Małgorzata, 2019, Gastrotricha - not only in sediments: new epiphytic species of Chaetonotida from the Jubilee Greenhouse of the Botanical Garden in Kraków, pp. 1-100 in European Journal of Taxonomy 511 on pages 23-35, DOI: 10.5852/ejt.2019.511, http://zenodo.org/record/2626854