General

Females (figs 1, 2, 3 and table 1): body medium-sized, stout, tapering at both extremities, more at posterior end. Cuticular framework provided with heavily sclerotized, transverse bars having branched ends, forming hexagonal blocks (fig. 2D–G) arranged in eight longitudinal rows. Ends of transverse bars of cuticle ramifying into 2, 3 or 4 finer processes that interlock with processes of adjacent bars to form rhomboids with a zigzag pattern, longitudinally (figs 2D, 3L). Dot-like punctations interspersed with transverse bars (fig. 2H). Left side without discernible ridges. Right and left sides of body annulated; annuli 2.0–2.5 μm wide in different body regions. Lip region offset, 10–11 μm in diameter; three distinct lobe-like lips on right side (fig. 2B), three lips with frilled margins on left side (fig. 2C); lips provided with minute inner labial sensilla, raised outer labial sensilla, four long setose cephalic sensilla (fig. 2B, C). Amphid apertures not seen. Stoma prismatic, rhabditoid type, about one-fifth to one-sixth of pharyngeal length or 2.3–2.6 times labial diameter. Cheilostom tubular, weakly cuticularized (figs 1C and 2B, C); gymnostom cuticularized, with parallel walls, stegostom surrounded by pharyngeal collar for about 25–35% of stoma length (fig. 1C); metastegostom with a fine denticle on each plate (fig. 1C). Telostegostom obscure. Glottoid apparatus absent (fig. 2B, C). Pharynx with weakly swollen or cylindroid corpus, 85–107 μm long, 4.0–5.5 times isthmus length or 59.7–65.3% of pharyngeal length. Isthmus 25–32 μm long. Basal bulb strong, oblong to square-shaped, 30–42 μm ×  22–27 μm, with grinder and single-chambered haustrulum. Nerve ring surrounding pharynx at 70–78% of pharyngeal length from anterior end. Secretory–excretory pore not visible. Body width at pharyngeal end 3.8–4.1 times labial diameter. Cardia 4–7 μm long with conical flaps. Intestinal cells large with prominent nuclei, boundary of intestinal lumen thin. Rectum length 3.0–3.5 times anal body diameter, terminating as a tube formed by external cuticular sheath. Reproductive system didelphic, amphidelphic. Ovaries dorsally reflexed with 2–3 tiers of oocytes in germinal zone. Anterior genital branch 2.6–2.8 times longer than posterior one. Posterior genital branch greatly reduced with small ovary having oocytes. Eggs not observed in utero. Vagina 15–23 μm long, with cuticularized lumen, anteriorly directed occupying a third to a half of corresponding body diameter. Vulva slit-like, post-equatorial. Distance between vulva and anus 3.2–4.4 times tail length. Tail 3.0–4.5 times anal body diameter long, uniformly tapering into a fine, usually dorsally curved, tip.

Fig. 1

Pterygorhabditis punctata n. sp.: (A) entire female; (B) entire male; (C) anterior end; (D) pharyngeal region; (E) female reproductive system; (F) male posterior region; (G) female posterior region.

Fig. 2

Pterygorhabditis punctata n. sp.: (A) anterior body region showing transverse cuticular bars (smooth and ramified ones); (B) anterior end with labial sensilla and stoma (right side); (C) anterior end with labial sensilla and stoma (left side); (D–G) body region (right side) showing cuticular pattern; (H) body region showing punctations; (I) male reflexed testis and a part of vas deferens; (J) female posterior region with anal cuticular sleeve; (K, L) male posterior region (lateral); (M) male posterior region (ventral) (scale bars = 10 μm).

Fig. 3

Comparison of anterior body region, cuticular ornamentation and male posterior region in species of Pterygorhabditis Timm, Reference Timm1957. (A, G, M) P. hungarica (after Andrássy, Reference Andrássy1982); (B, H, N) P. panopla (after Bernard, Reference Bernard1979); (C, I, O) P. superbus (after Huseni, Ahmad & Firdausi, Reference Huseni, Ahmad and Firdausi1997); (D, J, P) P. pakistanensis (after Timm, Reference Timm1957); (E, K, Q) P. saprophila (after Khan & Tahseen, Reference Khan and Tahseen2005); (F, L, R) P. punctata n. sp. (scale bars = 10 μm).

Table 1

Morphometric characteristics (measurements in μm) of Pterygorhabditis punctata n. sp. and Aspidonema formosa n. sp.; mean ± standard deviation (range).

a= body length/body diameter; b= body length/pharynx length; c= body length/tail length; c′ = tail length/anal body diameter; V= (distance from anterior region to vulva/body length) × 100; T= (length of testis/body length) × 100; G1 = (length of anterior gonad/body length) × 100; G2 = (length of posterior gonad/body length) × 100.

Males (figs 1, 2, 3, table 1): body slender, almost straight upon fixation. Similar to female in general morphological characters except smaller body size. Testis single, dorsally reflexed; reflexed part 38–67 μm long. Spicules long, slender, 3.0–3.2 times longer than cloacal body diameter with slightly differentiated capitula, fused distally (figs 2L, M, 3R). Gubernaculum small, spatula–shaped, about 20–27% of spicule length. Bursa reduced, open, pseudopeloderan type, leaving small tail spike free. Bursal papillae setose, nine pairs, pre-cloacal pair not seen; post-cloacal papillae in 3+3+P+1+2 configuration (figs 1F, 2K, M). Papillae GP1, GP2 and GP3 less spaced, robust; GP4 smaller and thinner, separated from robust GP5 and GP6; phasmids anterior to dorsally directed GP7; GP8 and GP9 closely placed near tail tip.

Type habitat and locality

Samples containing P. punctata n. sp. were collected from the shore of a canal at Bulandshahr (geographical coordinates: 28.40 296°N, 77.85 824°E), Uttar Pradesh, India.

Type specimens

Holotype female, five paratype females and two paratype males on slide, Pterygorhabditis punctata n. sp. no. NOSR/1–4 deposited in Nematode Collection, Department of Zoology, Aligarh Muslim University, Aligarh, Uttar Pradesh, India.

Diagnosis and relationships

Pterygorhabditis punctata n. sp. is characterized by a medium-sized body; presence of flattened hexagonal blocks arranged in eight longitudinal rows in both sexes, three lobe-like lips on the right side and three reduced lips with frilled margins on the left side; a weakly cuticularized cheilostom; each metastegostomal plate with a minute denticle, pharyngeal corpus uniformly wide; female reproductive system with a greatly reduced posterior branch and males with long, slender, distally fused spicules, a spatula-shaped gubernaculum, a reduced, pseudopeloderan bursa and nine pairs of prominently setose, post-cloacal genital papillae.

Pterygorhabditis punctata n. sp. most closely resembles P. pakistanensis Timm, Reference Timm1957 in morphometric and morphological details, but differs in having greater a (body length/body diameter: 13.5–16.3 vs. 11.0–13.1) and c (body length/tail length: 11.0–14.7 vs. 8.3–9.4) values; a lesser number (8 vs. 10–12) of flattened hexagonal cuticular blocks in the female; lips on left side frilled (vs. indistinct); each metastegostomal plate with one denticle (vs. denticle not reported); males with conspicuous spatula-shaped (vs. blunt) gubernaculum; GP1 and GP2 post-cloacal (vs. pre-cloacal) and only the fourth pair (vs. sixth and seventh pairs thin and smaller) and the bursa reduced (vs. moderately developed).

Pterygorhabditis punctata n. sp. resembles P. superbus Huseni, Ahmad & Firdausi, Reference Huseni, Ahmad and Firdausi1997 in most morphometric characteristics but differs in having a longer body (0.6–0.7 mm vs. 0.3–0.5 mm); greater V value ((distance from anterior region to vulva/body length) × 100: 65–67 vs. 57–60); left side with indiscernible ridges (vs. six longitudinal ridges); cheilostom simple (vs. cuticularized); posterior genital branch greatly reduced (vs. equal to anterior genital branch); vagina anteriorly directed (vs. at right angle to main body axis); and males with longer (79–86 μm vs. 51–60 μm) spicules; larger (21–23 μm vs. 13–15 μm), proximally spatula-shaped (vs. attenuated) gubernaculum and pre-cloacal papillae absent (vs. four pre-cloacal pairs).

The new species also resembles P. saprophila Khan & Tahseen, Reference Khan and Tahseen2005 in most morphometric details but differs in having a longer body (0.6–0.7 mm vs. 0.41–0.51 mm) with cuticle tightly applied (vs. forming wing) in anterior region; greater V value (65–68 vs. 53–54); left side with indiscernible ridges (vs. two faint longitudinal lines); faint (vs. conspicuous) cheilostom; lips on right side conspicuous, lobe–like (vs. indistinct); pharyngeal corpus weakly swollen or cylindrical (vs. strongly swollen); posterior genital branch greatly reduced (vs. equal to anterior genital branch) and males with longer (79–86 μm vs. 55–57 μm) spicules; larger (21–23 μm vs. 14–15 μm), proximally spatula-shaped (vs. attenuated) gubernaculum and nine pairs of genital papillae with pre-cloacal papillae absent (vs. four pre-cloacal pairs).

Etymology

The species epithet ‘punctata’ denotes the presence of fine yet conspicuous scattered punctations besides the ridges and a rhomboid system of markings.

Remarks

The morphological feature, e.g. metacorpus, could have been taken as a character of comparison with P. superbus Huseni, Ahmad & Firdausi, 1997; however, it has been stated to be cylindrical in the original description (p. 46 para. 1) but illustrated to be prominently swollen (fig. 3C) apud Huseni et al. (Reference Huseni, Ahmad and Firdausi1997). The new species seems to be a close relative of P. pakistanensis Timm, Reference Timm1957 in many aspects; however, there are few noticeable differences: besides the lesser number of cuticular blocks in females, the interlocking of transverse cuticular bars seems to be more complex (fig. 3L vs. 3J) in the present species. Even if the differences of metastegostomal tooth and allometric ratios (a and c) are overlooked, the other characters, namely a conspicuous spatula-shaped gubernaculum and a fairly reduced bursa with dissimilar configuration of papillae, make P. punctata distinct from P. pakistanensis. It further appears that in the original illustrations of P. pakistanensis Timm, Reference Timm1957, Figures 1B and 1D are not indicated with appropriate scale bars and Figures B, C, D and H seem to have been drawn at the same scale.

Andrássy (Reference Andrássy2005) raised the genus Pterygorhitis for those species of Pterygorhabditis that have 1–3 head shields, a markedly swollen corpus and relatively thicker spicules, and transferred Pterygorhabditis panopla and Pterygorhabditis hungarica to the former genus. The presence of the shield is a character that poses ambiguity. Pterygorhitis panopla has a single head shield as also confirmed by Holovachov et al. (Reference Holovachov, Esquivel and Bongers2003). The shield, in our opinion, can also be due to an artefact that may occasionally appear during the fixation or dehydration process. Therefore, it can be a supplementary character but not the differentiating one. Another feature, the swollen corpus, is too flimsy a character to have a diagnostic value on its own. Spicules which are equally long in Pterygorhitis only differ on account of thickness but that, too, is a comparative feature. Spicules as illustrated in the Costa Rica population of P. panopla (Holovachov et al., Reference Holovachov, Esquivel and Bongers2003, Figure 2F) look slightly different, with a ventral triangular process similar to that of some species of Rhabditidae. Therefore, instead of grouping these species into two genera separated merely on very minor characters, we prefer placing the two species P. panopla Bernard, Reference Bernard1979 (fig. 3B, H, N) and P. hungarica Andrássy, Reference Andrássy1982 (fig. 3A, G, M) under the ‘panopla’ species group, while the others are placed under the ‘pakistanensis’ species group (fig. 3D, J, P).

Amended diagnosis

Pterygorhabditis is characterized by small to medium-sized individuals with a relatively plump body; a cuticle with conspicuous transverse annulations, with the right side adorned with 6–12 longitudinal blocks having a rhomboidal pattern, demarcated by ridges; the left side bearing 2–6 longitudinal lines or ridges; the lip region bearing setose appendages; small amphids; stoma rhabdtitoid type usually with inconspicuous metastegostomal denticles; glottoid apparatus absent; pharyngeal collar absent or very small; pharyngeal corpus weakly developed to strongly swollen; female reproductive system didelphic, amphidelphic with vulva equatorial to slightly post-equatorial; males with very long spicules with variable thickness, usually fused at the tip, bursa generally reduced, asymmetrical, with 7–9 pairs of genital papillae.

The species of genus Pterygorhabditis can be differentiated on the basis of the type of longitudinal cuticular patterns on the right side, the number of the lines/ridges on the left side, the presence or absence of an oval shield in the anterior region, the shape/thickness of spicules and also the number and arrangement of male genital papillae. The other features, namely labial sensilla, metastegostomal structure, nature of the pharyngeal corpus, length of female gonad, position of vulva, etc. are the features that show considerable variation, hence they cannot be relied upon exclusively for species identification.

General

Female (figs 4, 5, 6 and table 1): body 0.28–0.32 mm long, plump, ventrally curved upon fixation, tapering at both extremities. Right side of body bearing two striated ridges, two rows of reticulate network, two rows of warts and a single mid-lateral row of round to ovoid shields (fig. 5I). Warts forming 35–48 pairs with smooth (fig. 5F) or bifid apices (fig. 5G); 2.5–5.0 μm high having faint, weakly developed skeletal rods within a few specimens (fig. 5H, I). Each two consecutive warts placed 5–8 μm apart with 4–6 fine ribs in between. Anterior warts up to level of gymnostom, and posterior ones slightly beyond rectum, are smaller. Striated ridges (figs 4E, 5E) form the outermost border of reticulate networks of hexagonal or polygonal pattern that surround the rows of warts and shields. Shields represent rounded, smooth membranous structures loosely fitting into large hexagonal/polygonal sockets/depressions alternate to wart pairs (fig. 5I). Shields are displaced from their position (fig. 5I) with a slight pressure or friction in a few specimens. Five longitudinal ridges present on left side of body (fig. 5K). Lip region set-off from adjoining body; inner and outer labial sensilla not distinct; cephalic sensilla with leaf-like bases, 6–8 μm long. Amphid apertures not seen. Cuticular fold at neck base not observed. Stoma rhabditoid-type, length about one-fourth of pharyngeal length or 2.5–3.0 times labial width. Cheilostom conspicuous, rod-like; gymnostom occupying more than 50% of stomal length; metastegostom anisomorphic (figs 4B, C, 5C), without armature. Telostegostom distinct. Pharynx with strongly swollen corpus having thickened lumen, narrow isthmus and ovoid, basal bulb 12–14 × 10–12 μm, with grinder and single-chambered haustrulum. Pharyngeal corpus 1.4–1.9 times longer than isthmus and basal bulb together. Body width at pharyngeal end 2.7–3.8 times labial width. Nerve ring encircling isthmus at 67–75% of pharyngeal length. Secretory–excretory pore and hemizonid not seen. Cardia conoid, 2–3 μm long. Intestine with wide lumen. Rectum 2.6–4.5 times anal body diameter long, extending into tube formed by external cuticle. Reproductive system didelphic, amphidelphic. Both genital branches equally developed. Ovaries large, dorso-laterally reflexed, with two rows of oocytes in germinal zone. Anterior ovary on right and posterior ovary on left side of intestine, both their apices crossing each other. Spermatheca and crustaformeria not distinguishable. Neither eggs nor spermatozoa observed in genital tract. Vagina length one-third of corresponding body diameter; vulva a transverse slit with an ovoid rim, slightly post-equatorial. Vulva–anus distance 4.9–6.6 times tail length. Tail conoid, uniformly tapering to a fine terminus.

Fig. 4

Female Aspidonema formosa n. sp.: (A) entire body; (B) anterior end; (C) pharyngeal region; (D) vulval region (ventral); (E) body region (left side) showing longitudinal ridges; (F) body region (right side) showing shields surrounded by warts; (G) reproductive system (anterior branch); (H) posterior region.

Fig. 5

Female Aspidonema formosa n. sp.: (A) anterior end showing rectangular cuticular shields; (B) anterior region showing the level of first wart pair with respect to stoma; (C) anterior end showing labial sensilla; (D) pharyngeal region; (E) body region (left side) showing striated ridge; (F, G) body region (right side) showing warts; (H, I) body region showing dot-like pattern and shields; (J) reproductive system; (K) posterior region (scale bars = 10 μm).

Fig. 6

Cuticular ornamentation in species of Aspidonema (Sachs, Reference Sachs1949) Andrássy, Reference Andrássy1958: (A) A. stammeri (after Meyl, Reference Meyl1961); (B, C) A. scheucherae (after Meyl, Reference Meyl1961; Holovachov & Bongers, Reference Holovachov and Bongers2001); (D) A. ruehmi (after Meyl, Reference Meyl1961); (E) A. weingartnerae (after Meyl, Reference Meyl1961); (F) A. formosa n. sp. (scale bars = 10 μm).

Male: unknown.

Type habitat and locality

Aspidonema formosa n. sp. was obtained from a small ditch (alluvium soil rich in organic matter) at Sikandra Rao, Aligarh, Uttar Pradesh, India.

Type specimens

Holotype female and eight paratype females on slide Aspidonema formosa n. sp. NOA/1–6, deposited in the Nematode Collection, Department of Zoology, Aligarh Muslim University (geographical coordinates: 27.9108°N, 78.0797°E), Aligarh, Uttar Pradesh, India.

Diagnosis and relationships

Aspidonema formosa n. sp. is characterized by a small body with the right side having two rows of 35–48 conical to bifid warts, circular in outline, flanking a median row of oval to round, smooth membranous shields and flanked by a well-developed network on the sides; warts with faint or indiscernible skeletal rods; anisomorphic metastegostom without discernible armature, swollen pharyngeal corpus, female genital branches equal-sized, reflexed parts of ovaries crossing each other, vulva slightly post-equatorial and males unknown.

Aspidonema formosa n. sp. most closely resembles A. ruehmi (Sachs, Reference Sachs1949) Goodey, 1963 in most morphometric and morphological characteristics, but differs in having a relatively greater c value (12–18 vs. 11–13); warts circular (vs. transversely oval) in outline, greater number of wart pairs (35–48 vs. 30–34) supported by no, or a weakly developed, skeletal rod (vs. two distinct internal rods) and in the absence of males (vs. males present in A. ruehmi apud Andrássy, Reference Andrássy1983).

The new species differs from closely related A. stammeri (Sachs, Reference Sachs1949) Andrássy, Reference Andrássy1958 in having greater c (12–18 vs. 9–12) and smaller V values (54–56 vs. 59–64); fewer pairs of warts (35–48 vs. 50–59); middle row of weak and membranous (vs. cuticularized) shields with those at anterior and posterior extremities large and rectangular (vs. small, rounded) in shape; and in the absence of males (vs. males present).

Etymology

The species name is derived from the Latin word (formosus =  beautiful) denoting its beautiful cuticular ornamentation.

Remarks

The genus Aspidonema is recorded for the first time from India. All five previously described species were reported from Germany, Hungary and Turkey, and were extracted from compost (Sachs, Reference Sachs1949; Andrássy Reference Andrássy1983), horse and cow dung (Andrássy, Reference Andrássy2005) or rotting material (Holovachov & Bongers, Reference Holovachov and Bongers2001).

Aspidonema formosa n. sp. was collected from a ditch; however, it was in close proximity to a farmyard manure storage pit. The species is represented by a population of females only. Amixis could be the probable mode of reproduction, although this is subject to verification. It is a fact that the morphometrics of all the congeners do not vary significantly, except for very few attributes. Hence, the differentiation has to be based entirely on the morphological characters that are relatively consistent and reliable. The shape of the labial sensilla, metastegostomal structure, nature of pharyngeal corpus, length of female gonad, position of vulva, etc., all have considerable intra-population variation and hence are not reliable for differentiation of species. The types of cuticular ornamentation, i.e. the number and structure of warts, shields and networks, besides the number of longitudinal ridges on the left side, form important characters for differentiation. Figure 6 compares the cuticular ornamentation in different species so as to draw the line of distinction. The species A. stammeri, A. ruehmi and A. formosa n. sp. show a more or less similar nature of ornamentations. However, besides their number and pattern, the proportionate sizes of the warts and shields also have distinctive value. The other congeners, namely A. sheucharae and A. weingartnerae, differ significantly on account of dissimilar warts and shields. Holovachov & Bongers (Reference Holovachov and Bongers2001) gave a comprehensive description of A. sheucharae with detailed scanning electron microscopy to reveal finer details of the cuticle. Aspidonema formosa markedly differs from A. sheucherae in the shape of warts (rounded vs. triangular), shape of shields (rounded to oval vs. ellipsoidal) and the nature of the network (polygonal vs. elongate/rectangular type).

Amended diagnosis

Aspidonema is characterized by small-sized nematodes with the right side ornamented with paired warts flanking a median row of larger, usually round to oval, membranous shields and surrounded by a punctated network latero-dorsally and latero-ventrally; the left side bearing lines or thin ridges; the lip region expanded with setose cephalic sensilla; stoma rhabditoid, usually with sclerotized cheilostom, metastegostom usually without denticles, occasionally anisomorphic; pharyngeal collar short; pharyngeal corpus usually swollen; female reproductive system didelphic, amphidelphic with reflexed ovaries; vulva equatorial or post-equatorial in position; rectum long; males with long, slender spicules; bursa asymmetrical and tail forked distally in males.

The genus has four known species besides A. formosa n. sp. The species A. sachsi has not been considered among the valid species of the genus as it is based on a single male specimen. A species needs to sustain itself and, in order to produce its progeny, the female is required, which is unknown in this case, hence the status of the species is uncertain. Also, a number of morphological characters are not shown by males or have disparity with female characters; therefore, A. sachsi is not considered to be a valid species.