Diplogastrellus didelphis, 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 : 4-9

Diplogastrellus didelphis sp. nov.

urn:lsid:zoobank.org:act:1B249AFA-2213-4700-A004-C4771D5BAF20

Figs 1–2 , 17–19 ; Tables 1, 7–8

Diagnosis

The new species Diplogastrellus didelphis sp. nov. is characterised by finely punctated cuticle ( Fig. 2H ); a narrow stoma longer than wide; a medium-sized dorsal tooth with ventrally directed apex; amphidial apertures small, elliptical, at the base of gymnostom; oblong median bulb with valve plates and a pyriform basal bulb; amphidelphic reproductive system, a large uterine pouch filled with sperm ( Fig. 2I ); spicules separate, strongly built, ventrally arcuate with a 90º curvature; proximally sickle-shaped or notched with a long anteriorly-directed dorsal arm and a short ventral arm, distal end thin and delicate with a sleeve and nine pairs of genital sensilla.

Etymology

The name of the species is based on the didelphic-amphidelphic gonad.

Material examined

Holotype

INDIA • ♀; Uttar Pradesh, District Muzaffarnagar ; 29°31′27″ N, 77°38′38″ E; isolated from rotting banana rhizome; slide reference number AMU/ZD/NC/ Diplogastrellus didelphis /1.

Paratypes

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

Description

Adult

Body slender, 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 ( Fig. 2H ). Lip region round, continuous with body contour. Lips six, amalgamated, each bearing a small papilliform labial sensilla. Amphidial apertures small, elliptical, 6–7 µm from anterior end of stoma, at the base of gymnostom. Stoma narrow, tubular, longer than wide, about 10–11 µm in depth. Cheilostom slightly 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 medium-sized tooth, with ventrally directed apex, subventral walls without armature. Pharynx with slender 65–78 µm long, muscular corpus of uniform diameter; median bulb set off from corpus, oblong, 23–29 µm long with strong valve plates. Isthmus 32–42 µm long, narrow, conspicuously differentiated from median bulb. Basal bulb small, pyriform, glandular, 12–15× 9–10 µm, only slightly expanded from isthmus without any valve plate or grinder. Dorsal pharyngeal gland nucleus usually prominent, located near base of basal bulb. Nerve ring encircling isthmus in anterior half, located at 73–77% of pharyngeal length. Hemizonid and excretory pore not visible. Cardia well-developed, 5 µm long, consisting of three flaps, one dorsal and two ventro-sublateral. Intestine composed of dark granulated cells with prominent nuclei, intestinal lumen uniformly wide, 5–6 µm without any bacterial pouch. Rectum 0.9–1.1 times anal body diameter long; rectal glands distinct.

Female

Reproductive system didelphic, amphidelphic, anterior gonad on right side and posterior on left side of intestine. Posterior branch usually smaller than the anterior. Ovaries long reversed, with distal part of ovaries 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, tubular. Spermatheca not set off from uterus, with distinctly narrower walls, containing sperm. Uterus divisible into a distal smaller muscular part and proximally placed longer, glandular part made up of large cells and narrow lumen. A large uterine pouch, 35–80 µm long, opens into reproductive tract at uterus-vagina junction, filled with sperm. Vagina narrow, tubular, almost at right angle to longitudinal body axis, 6–7 µm long about one-fourth of corresponding body diameter. Vulval opening small, elliptical, flushing with body contour. Vulva-anus distance 7.2–9.1 times vulval body diameter. Phasmids located at a level 1.3–1.7 of anal body diameter posterior to anus. Tail long, filiform 0.8–1.1 times vulva-anus distance, divided into two parts, an anterior short conoid part and a posterior longer filamentous part.

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 distally followed by single row proximally. Vas deferens a long tube containing spermatocytes transforming into spermatozoa, tapering to an ejaculatory duct. Spicules paired, separate, strongly built, ventrally arcuate with a 90º curvature, 1.4–1.7 times cloacal body diameter long. Manubrium round connected to calamus/lamina complex expanding into ventral conoid process, posteriorly tapering to a pointed distal tip. Gubernaculum stout, 58–61% of spicule length, proximally sickle-shaped or notched with a long anteriorly-directed dorsal arm and a short ventral arm, distal end thin and delicate with a sleeve. 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, v2d, v3 / v4, ad, ph, (v5, v6, v7), pd. Precloacal pair v1 located more than one cloacal diameter anterior to cloaca; v2 and v3 closely placed; v3 just anterior and v4 closely posterior to cloaca; ad less than one cloacal body diameter posterior to cloaca, v5–7 grouped; pd far posterior to v7. Phasmids pore-like, 0.7–1.1 anal body diameter posterior to cloacal opening.

Remarks

Diplogastrellus didelphis sp. nov. comes close to D. gracilis in most morphometric and morphological characteristics but differs in the shape of stoma (narrow, tubular vs comparatively broader), structure of dorsal tooth (anterio-ventral margin lacking serration vs serrated anterio-ventral margin), position of amphids (at the base of gymnostom vs at the base of cheilostom), female reproductive system (amphidelphic vs mono-prodelphic), uterine pouch (present vs absent), size and shape of spicules (30– 31 µm; strongly built, calamus/lamina complex expanded into ventral conoid process vs 42–58 µm; long, attenuated, calamus/lamina complex not expanded), shape of gubernaculum (proximally notched with a long dorsal arm vs keel-like proximal part) and in the arrangement of genital sensilla (v3 anterior to cloaca vs v3 adcloacal).

The new species differs from D. monhysteroides in the shape of dorsal tooth (ventrally directed apex vs anteriorly directed apex), shape of median bulb (oblong vs ovoid), female reproductive system (amphidelphic vs mono-prodelphic), uterine pouch (present vs absent), shape of spicules (strongly arcuate with a 90º curvature to a pointed distal end vs smoothly arcuate to a curved distal end), structure of gubernaculum (proximally notched with a long dorsal arm, distal part thin with a sleeve vs proximally curved, distal part with a large rectangular sleeve) and arrangement of genital sensilla (v2 anterior to cloaca far away from v1 vs v2 more anterior near the spicule head, close to v1).

The new species resembles D. metamasius in most morphometric characters but differs in having more slender body (a = 26.0–31.6 vs 16.1–22.2 in females), female reproductive system (amphidelphic vs mono-prodelphic), by uterine pouch (present vs absent), shape of spicules (strongly arcuate with a 90º curvature vs slightly curved), structure of gubernaculum (proximally notched with a long dorsal arm, distal sleeve present vs proximally notched, sleeve absent) and arrangement of genital sensilla (v2 anterior to cloaca within the spicular range vs v2 more anterior beyond the spicule head).

Diplogastrellus didelphis sp. nov. differs from D. graciloides in the position of amphids (at the base of gymnostom vs posterior to the base of stoma), female reproductive system (amphidelphic vs mono-prodelphic), uterine pouch (present vs absent), size of spicules (30–31 µm vs 24.5 µm), structure of gubernaculum (proximally notched with a long dorsal arm, distal sleeve present vs caudally projected keel-like without sleeve) and arrangement of genital sensilla (9 pairs; v1 beyond the spicular range vs 8 pairs; v1 located near the spicule head; v7 absent).

Diplogastrellus didelphis sp. nov. resembles Acrostichus medius Tahseen et al., 2016 in having didelphic reproductive system in females amphidelphic, and by presence of uterine pouch and stomal morphology. Acrostichus medius shows features common to both Diplogastrellus and Acrostichus ; however, Diplogastrellus didelphis markedly differs from it in the structure of spicules (strongly arcuate with about 90º curvature vs robust spicules with hood-like capitula, appearing deeply forked distally with fine extensions and a ventral attenuated arm) and gubernaculum (proximally notched with a long dorsal arm, distal sleeve vs curved and tapering proximal end and distal end with slight protuberances), bursa (absent vs with rudiments confined to posterior four genital pairs) in addition to other morphometric characters.

Figures

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

Fig. 2. Diplogastrellus didelphis sp. nov. A–F, H–I. Holotype, ♀ (AMU/ZD/NC/Diplogastrellus didelphis sp. nov./1). F–G, J. Paratype, ♂ (AMU/ZD/NC/Diplogastrellus didelphis sp. nov./2–9). A. Pharyngeal region. B. Anterior region showing stoma (lateral view). C. Anterior region showing amphid. D. Female reproductive system showing anterior branch. E. Female posterior region. F. Male genital papillae. G, J. Male posterior region showing spicules and gubernaculum. H. Cuticular punctations. I. Uterine pouch. The arrowheads in C, F and I indicate amphidial aperture, genital sensilla and uterine pouch, 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).