Diplogastrellus gracilis ( Bütschli, 1876 )

Mumtaz, Sabia, Bashir, Ishrat, Ahmad, Irfan & Tahseen, Qudsia, 2025, New insights into Diplogastrellus Paramonov, 1952 (Nematoda: Rhabditida: Diplogastroidea) with three novel and three known species from India, European Journal of Taxonomy 1008, pp. 1-50 : 22-27

Diplogastrellus gracilis ( Bütschli, 1876)

Figs 9–11 , 17–19 ; Tables 4 , 7–8

Emended diagnosis

Diplogastrellus gracilis is characterised by a stoma longer than wide; cuticle with transverse and longitudinal striations; elliptical amphidial aperture, at the base of cheilostom; massive dorsal tooth with ventrally directed apex, anterio-ventral margin serrated; small tooth on each subventral wall; pharynx well-developed, muscular oblong metacorpal bulb with valve plates, narrow isthmus and a pyriform basal bulb; mono-prodelphic reproductive system; spicules thin, long, attenuated, strongly arcuate with oval manubrium, smoothly arcuate to a pointed distal end; gubernaculum 33 – 40% of spicule length, with lateral sleeve at distal end surrounding terminal region of spicules and a prominent, keel-like proximal part. and nine pairs of genital sensilla – constituting two precloacal, two adcloacal and five postcloacal pairs.

Material examined

INDIA • 10 ♀♀, 10 ♂♂; Uttar Pradesh, District Aligarh ; 27°54′24″ N, 78°4′36″ E; extracted from rotting banana rhizome; slide reference number AMU/ZD/NC/ Diplogastrellus gracilis / 1–10 .

Description

Adult

Body slender, medium-sized, less than 1 mm long; almost straight after fixation, tapering only very slightly anteriorly, but more posteriorly forming a filiform tail. Cuticle with fine transverse and longitudinal striations. Cuticular punctations fine, transversely arranged. Lateral fields with two conspicuous spaced ridges about 8.6–12.0% of maximum body width. Lip region continuous with body contour. Lips six, amalgamated, bearing a small papilla each. Amphidial apertures elliptical, 3 µm from anterior end of stoma, at the base of cheilostom. Stoma longer than wide, about 8–11 µm in depth. Cheilostom longer than wide, cheilorhabdions straight, cheilorhabdial flaps six, protruding above labial contour, gymnostom anisotopic, dorsal wall shorter than subventrals. Stegostom anisotopic and anisomorphic, dorsal metastegostomal wall with a large dorsal tooth, bulging into stoma, apex ventrally directed almost reaching the base of the ventral gymnostomal wall. Posterio-ventral aspect of tooth strongly cuticularised, concave; anterio-ventral aspect not cuticularised with an irregular surface. Subventral walls with small tooth each. Pharynx with slender 58–79 µm long, muscular corpus of uniform diameter; median bulb set off from corpus, oblong, 17–22 µm long with strong valve plates. Isthmus 23–40 µm long, narrow, conspicuously differentiated from median bulb. Basal bulb small, pyriform, glandular, 14–17×10–13µm, only slightly expanded from isthmus without any valve plate or grinder. Nerve ring encircling isthmus in anterior half, located at 70–84% pharyngeal length. Excretory pore and hemizonid inconspicuous. Deirids at the level of basal bulb. Cardia small, 3–4 µm long, consisting of three flaps, one dorsal and two ventro-sublateral. Intestine composed of dark granulated cells with prominent nuclei intestinal lumen uniformly 11–13 µm wide, without any bacterial pouch. Rectum 1.0–1.6 times anal body diameter long; rectal glands distinct.

Female

Reproductive system mono-prodelphic. Ovary reversed on right side of intestine, distal part of ovary not reaching the level of vulva. Oocytes with large nuclei, arranged in multiple rows in germinal zone and single row in maturation zone. Oviduct long, narrow, connecting spermatheca and ovary. Spermatheca expanded, generally filled with sperm, continuous with oviduct but separated by a constriction from uterus. Uterus divisible into a distal smaller muscular part and proximally placed longer glandular part made up of large cells and narrow lumen. Vagina tubular, inclined anteriorly, 11–13 µm long about half of the corresponding body diameter long. Vulval opening circular, vulval lips slightly protuberant. Post-uterine sac absent. Vulva-anus distance 1.0–1.7 times vulval body diameter. Phasmids located at about 1.3–2.1 anal body diameter posterior to anus. Tail long, filiform 4.8–7.8 times vulva-anus distance.

Male

Similar to females in general morphology but smaller in size. Reproductive system monorchic, testis reflexed laterally, on right side of intestine. Spermatocytes arranged in two rows in anterior reflexed part, well-developed spermatocytes in anterior half of non-reflexed part, as multiple rows in next half and containing small sperm in remaining gonad. Vas deferens a long tube tapering to an ejaculatory duct. Spicules long, thin, attenuated, strongly arcuate, 2.6–2.9 times cloacal body diameter long. Capitulum oval, calamus/lamina smoothly attenuated towards a pointed distal tip. Gubernaculum 33–40% of spicule length, with lateral sleeve and a prominent, proximal keel-like part. Tail divisible into two parts, a short conoid part and a longer filamentous part. Genital sensilla nine pairs; two pairs precloacal, two pairs adcloacal and five pairs postcloacal. Genital sensilla formula: v1, v2d, v3 / v4, ad, ph, (v5, v6, v7), pd. Precloacal pair v1 located more than one cloacal body diameter anterior to cloaca; v2d slightly anterior to cloaca; v3 and v4 adcloacal; ad less than one cloacal body diameter posterior to cloaca; pd far posterior to v7. Phasmids pore-like, at the level of v5, 0.7–0.9 anal body diameter posterior to cloacal opening.

Remarks

The original description of D. gracilis was given by Bütschli (1876) and further described or reported by Goodey (1929), Paramonov (1952), Weingärtner (1955), Timm (1961) and Kiontke & Sudhaus (1996). Later, Khan et al. (2008) provided the detailed description of the species collected from compost of mushroom, India. Our specimens’ descriptions and morphometric measurements concur well with those of the original specimens of D. gracilis described by Bütschli (1876). However, differences were observed in total length of body in both sexes (L = 735–817 µm vs 1350–1390 µm in females and 536–733 µm vs 1000–1070 µm in males), longer pharynx (b = 4.9–6.4 vs 7.3) in females, longer tail (c = 4.8–5.7 vs 7.1) in males, and structure of dorsal tooth (massive tooth with serrated anterior-ventral margin vs smaller tooth lacking serration). The population reported by Khan et al. (2008) indicates a wide range of values (L = 666–750 µm, a = 26.8–32.6, b = 5.2–5.9, c = 3.5–3.8, c’ = 11.1–12.0, V = 67.3–68.9% in females; spicule = 50–57 µm, gubernaculum = 20–25 µm) which nearly overlapped with the values of our population.

Figures

Fig. 9. Diplogastrellus gracilis (Bütschli, 1876).A, C–F. ♀ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). B, G–H. ♂ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). A. Entire female. B. Entire male. C. Anterior region showing stoma (dorsoventral view). D. Pharyngeal region. E. Female reproductive system. F. Female posterior region. G. Male posterior region. H. Spicule and gubernaculum.

Fig. 10. Diplogastrellus gracilis (Bütschli, 1876). A–I. ♀ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). J–L. ♂ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). A. Pharyngeal region showing procorpus and median bulb. B. Anterior region showing stoma (lateral view). C. Anterior region showing amphids (dorsoventral view). D. Reflexed part of ovary. E. Uterus (glandular part). F. Vulval region. G. Female posterior region. H. Lateral lines. I. Cuticular punctations. J. Genital papillae (v5–7). K–L. Male posterior region showing spicules and gubernaculum. The arrowheads in C, H–J and L indicate amphidial aperture, lateral lines, fine punctations, grouped genital papillae and attenuated spicular distal end, respectively. Scale bars: A–B, E–G = 20 µm; C–D, H–L = 10 µm.

Fig. 11. Diplogastrellus gracilis (Bütschli, 1876). A–D, G. ♀ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). E–F. ♂ (AMU/ZD/NC/Diplogastrellus gracilis/1–10). A. Anterior region showing labial papillae and cheilorhabdial plates.B. Anterior region showing amphid. C. Pharyngeal region showing cuticular striations. D. Vulval region. E–F. Male posterior region showing genital papillae. G. Female posterior region. The arrowheads in E–F indicate genital papillae. Scale bars = 10 µm.

Fig. 17. Map showing the worldwide geographical locations of the holotypes of species of Diplogastrellus Paramonov, 1952.

Fig. 18. Cladogram (constructed manually) showing the relationships of the species of Diplogastrellus Paramonov, 1952. Apomorphic morphological traits are designated by black squares and plesiomorphic traits by white squares.

Fig. 19. Cladistic analysis of the species of the genus Diplogastrellus Paramonov, 1952, indicating the position of the new species D. didelphis sp. nov., D. longipharyngis sp. nov., and D. robustus sp. nov. The phylogenetic tree was constructed for nineteen species using PAUP ver. 4.0. (Swofford 2002).