Diplogastrellus robustus, Mumtaz & Bashir & Ahmad & Tahseen, 2025

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 : 15-21

Diplogastrellus robustus sp. nov.

urn:lsid:zoobank.org:act:36D4BB43-EC22-481D-BE18-CDDF4784140D

Figs 6–8 , 17–19 ; Tables 3 , 7–8

Diagnosis

The new species Diplogastrellus robustus sp. nov. is characterised by a narrow stoma longer than wide; small, elliptical amphidial aperture, at the level of gymnostom; a medium-sized dorsal tooth with ventrally directed apex; pharynx well-developed, muscular ovoid metacorpal bulb with valve plates, narrow isthmus and a pyriform basal bulb; amphidelphic or mono-prodelphic reproductive system with a post-uterine sac; spicules robust, heavily cuticularized, smoothly curved to a blunt distal end; boat-like gubernaculum with a sleeve and nine pairs of genital sensilla.

Etymology

The name of the species is based on the robust spicule.

Material examined

Holotype INDIA • ♀; Kerala, District Kottayam ; 9°35′55″ N, 76°30′39″ E; isolated from soil near ginger plantation; slide reference number AMU/ZD/NC/ Diplogastrellus robustus /1.

Paratypes INDIA • 10 ♀♀, 10 ♂♂; same data as for holotype; slide reference number AMU/ZD/NC / Diplogastrellus robustus /2–9 .

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 striations. Lip region round, continuous with body contour. Lips six, amalgamated, each bearing a small papilliform labial sensilla. Amphidial apertures small, elliptical, 5–6 µm from anterior end of stoma, at the level of gymnostom. Stoma longer than wide, about 9–11 µm in depth. Cheilostom longer than wide, cheilorhabdions arched inward anteriorly, cheilorhabdial flaps six, protruding above labial contour; gymnostom anisotopic, dorsal wall shorter than subventrals. Stegostom anisotopic and anisomorphic, dorsal metastegostomal wall with a ventrally directed medium-sized tooth. Posterio-ventral aspect of dorsal tooth heavily cuticularized, supported posteriorly by cuticularised ridge. Subventral walls without armature. Pharynx with slender 78–88 µm long, muscular corpus of uniform diameter; median bulb set off from corpus, ovoid, 21–25 µm long with strong valve plates. Isthmus 33–57 µm long, narrow, conspicuously differentiated from median bulb. Basal bulb small, pyriform, glandular, 18–21× 14–17 µm, only slightly expanded from isthmus without any valve plate or grinder. Nerve ring encircling isthmus in the middle or sometimes in the anterior half, located at 64–76% of pharyngeal length. Hemizonid posterior to nerve ring, 65–85% of pharyngeal length. Excretory pore posterior to hemizonid, 69–88% of pharyngeal length. Cardia well-developed, 3–4 µm long, consisting of three flaps, one dorsal and two ventro-sublateral. Intestine composed of dark granulated cells with prominent nuclei and intestinal lumen uniformly wide, 8–10 µm without any bacterial pouch. Rectum 1.0–1.2 times anal body diameter long; rectal glands distinct.

Female

Reproductive system mono-prodelphic or amphidelphic. Anterior branch on the right and posterior on the left side of intestine. Ovary long reversed, extending beyond the level of vulva. Oocytes with large nuclei, arranged in multiple rows in germinal zone and single row in maturation zone. Oviduct narrow, tubular. Spermatheca expanded, not set off from uterus, with distinctly narrower walls, containing sperm. In most specimens, posterior genital branch appears to be reduced with sperm in the anterior part and vacuolated, degenerated cells in posterior part; sometimes posterior branch represented by a post-uterine sac. In two specimens, the posterior genital branch appeared well-developed and functional (amphidelphic). Uterus divisible into a distal smaller muscular part and proximally placed longer, glandular part made up of large cells and narrow lumen. Vagina short, at right angle to longitudinal body axis, 7–8 µm or about one-fourth of corresponding body diameter long. Vulval opening large, elliptical. Vulva-anus distance 5.6–7.9 times vulval body diameter. Phasmids located at a level 1.1–1.5 anal body diameter posterior to anus.

Males

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. Vas deferens a long tube narrowing posteriorly to form an ejaculatory duct. Spicules robust, strongly ventrally arcuate 1.2–1.5 times cloacal body diameter long. Manubrium hood-like, lamina/calamus complex expanded posterior to manubrium, and then smoothly tapering to a blunt distal tip. Gubernaculum slender, boat-shaped, 51–56% of spicule length, proximally curved, provided with a sleeve followed by a pointed distal end. Tail divisible into two parts, a short conoid part and a longer filamentous part. Genital sensilla nine pairs; three pairs precloacal and six pairs postcloacal. Genital sensilla formula: v1, v2, v3d, v4, ad, ph, (v5, v6, v7), pd. Precloacal pair v1 located just anterior to the spicule head; v2 and v3d at the same level, anterior to cloaca and v4 posterior to cloaca, ad less than one cloacal body diameter posterior to cloaca, v5–7 grouped, located just anterior to base of filiform tail spike. Phasmids pore-like, posterior to ad, 1.0–1.3 anal body diameter posterior to cloacal opening; pd slightly posterior to v7.

Remarks

Diplogastrellus robustus sp. nov. comes close to D. graciloides in most morphometric and morphological characteristics but differs in having more robust body (MBD = 27–41 µm vs 20–26 µm in females; 26–38 µm vs 18–21 µm in males), by position of amphids (at the level of gymnostom vs posterior to the base of stoma), shape of median bulb (ovoid vs oblong), length of the flexure of ovary (extending beyond the level of vulva vs not reaching the level of vulva), structure of spicules (robust, hood-like manubrium, blunt distal end vs slender, rounded manubrium, curved distal end), structure of gubernaculum (slender, boat-shaped, with distal sleeve vs globose, keel-like projection, without distal sleeve) and number of genital papillae (9 pairs; v4 less than one cloacal diameter posterior to cloaca vs 8 pairs; v4 more than one cloacal diameter posterior to cloaca, v7 absent).

The new species differs from D. metamasius in the shape of median bulb (ovoid vs oblong), position of vulva (posteriorly located, 59–64% vs anterior, 48–56%), size of post-uterine sac (longer than vulval body diameter vs shorter than vulval body diameter), shape and size of spicules (31–36 µm; hood-like manubrium, with blunt distal end, vs 23.0–30.5 µm; small rounded manubrium, with pointed distal end), shape of gubernaculum (boat-shaped with distal sleeve vs keel-like without distal sleeve) and arrangement of genital sensilla (v4 slightly less than one cloacal diameter posterior to cloaca vs v4 just posterior to cloacal slit).

Diplogastrellus robustus sp. nov. differs from the new species D. didelphis sp. nov. in the position of amphids (at the anterior part of gymnostom vs at the base of gymnostom), shape of median bulb (ovoid vs oblong), length of the flexure of ovary (extending beyond the level of vulva vs not reaching the level of vulva), uterine pouch (absent vs present), structure of spicules (robust, hood-like manubrium, calamus/ lamina complex not expanded with blunt distal end vs slender, rounded manubrium, calamus/lamina complex expanded into ventral conoid process with pointed distal end), structure of gubernaculum (boat-shaped, with distal sleeve vs proximally sickle-shaped, long curved dorsal arm and a short ventral arm with a distal sleeve) and arrangement of genital papillae (pd slightly posterior to v7 vs pd far posterior to v7).

Diplogastrellus robustus sp. nov. also differs from the new species D. longipharyngis sp. nov. in having more robust body (MBD = 26–38 µm vs 20–23 µm in males), position of amphids (at the anterior part of gymnostom vs at the base of dorsal tooth), length of stoma (10–12 µm vs 5–6 µm in females; 9–11 µm vs 6 µm in males), isthmus (shorter than corpus vs longer than corpus), length of the flexure of ovary (extending beyond the level of vulva vs not reaching the level of vulva), size and shape of spicules (31–36 µm; robust, hood-like manubrium, with blunt distal end vs 25–27 µm, slender, rounded manubrium with pointed distal end), structure of gubernaculum (boat-shaped, with distal sleeve vs triangular, proximally notched without distal sleeve) and arrangement of genital papillae (v7 grouped and pd slightly posterior to v7 vs v7 separated from v5, v6 and pd at the level of v7).

Figures

Fig. 6. Diplogastrellus robustus sp. nov. A, C–F, H. Holotype, ♀ (AMU/ZD/NC/Diplogastrellus robustus sp. nov./1). B, G, I. Paratype, ♂ (AMU/ZD/NC/Diplogastrellus robustus sp. nov./2–9). A. Entire female. B. Entire male. C. Anterior region showing stoma. D. Pharyngeal region. E–F. Female reproductive system. G. Male posterior region showing spicule and gubernaculum. H. Female posterior region. I. Spicule and gubernaculum.

Fig. 7. Diplogastrellus robustus sp. nov., paratype, ♀ (AMU/ZD/NC/Diplogastrellus robustus sp. nov./2– 9). A, C–D. Posterior branch showing reduced gonad contains sperm in the anterior part and vacuolated degenerated cells in the posterior part. B. Post-uterine sac.

Fig. 8. Diplogastrellus robustus sp. nov. A–E, G, I. Holotype, ♀ (AMU/ZD/NC/Diplogastrellus robustus sp. nov./1). F, H, J. Paratype, ♂ (AMU/ZD/NC/Diplogastrellus robustus sp. nov./2–9). A. Pharyngeal region. B. Anterior region showing stoma. C. Female posterior region. D. Female reproductive system showing anterior branch. E, I. Posterior branch (female gonad). G. Vulval opening. F, H. Male posterior region showing spicules and gubernaculum.J. Male genital papillae. The arrowheads in E and H–J indicate posterior genital branch, sleeve and genital papillae, respectively. 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).