Diplogastrellus graciloides ( Skwarra, 1921 )

Diplogastrellus graciloides ( Skwarra, 1921) View in CoL

Figs 12–13 View Fig View Fig , 17–19 View Fig View Fig View Fig ; Tables 5, 7–8

Diplogaster microstoma Goodey, 1929: 27–62 View in CoL , figs 25–27.

Diplogaster inaequidens Paesler, 1946: 87–128 View in CoL .

Emended diagnosis

Diplogastrellus graciloides is characterised by a narrow stoma longer than wide; elliptical amphidial aperture, posterior to the base of stoma; massive dorsal tooth with ventrally directed apex, 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 with a post-uterine sac; spicules slender with oval manubrium, smoothly arcuate to a curved distal end; globose gubernaculum with serrated proximal part and pointed distal tip and eight pairs of genital sensilla – with three precloacal and five postcloacal pairs and v7 absent.

Material examined

INDIA • 10 ♀♀, 10 ♂♂; Uttar Pradesh, District Muzaffarnagar ; 29°31′27″ N, 77°38′38″ E; extracted from rotting banana rhizome; slide reference number AMU/ZD/NC/ Diplogastrellus graciloides / 1–10 GoogleMaps .

Description

Adult

Body slender, medium-sized, less than 1 mm long; almost straight after fixation, tapering only very slightly anteriorly, but more conspicuously posteriorly to a long filiform tail. Cuticle with fine transverse striations, lateral fields inconspicuous. Lip region round, continuous with body contour. Lips six, amalgamated, each bearing a small papilla. Amphidial apertures elliptical, 13–14 µm from anterior end, just posterior to the base of stegostom. Stoma narrow, 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 large tooth, having ventrally directed apex. Posterio-ventral aspect strongly cuticularized, smooth. Anterio-dorsal aspect not cuticularized. Each subventral wall provided with a small tooth. Pharynx with slender 74–89 µm long, muscular corpus of uniform diameter; median bulb set off from corpus, elongate, 22–30 µm long with strong valve plates. Isthmus 38–48 µm long, narrow, conspicuously differentiated from median bulb. Basal bulb small, pyriform, glandular, 13–21× 9–12 µm, only slightly expanded from isthmus without any valve plate or grinder. Nerve ring encircling isthmus in anterior half, located at 66–71% of pharyngeal length. Hemizonid posterior to nerve ring, 67–72% of pharyngeal length. Excretory pore just posterior to hemizonid, 70–74% of pharyngeal length. Cardia well-developed, 3 µm long, consisting of three flaps, one dorsal and two ventro-sublateral. Intestine composed of dark granulated cells with prominent nuclei, intestinal lumen 6–8 µm wide, without any bacterial pouch. Rectum 1.0–1.4 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, tubular, connecting spermatheca and ovary. Spermatheca expanded, not set off from uterus but 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. Vagina narrow, tubular, almost at right angle to longitudinal body axis, 5–6 µm long, about one-fifth of corresponding body diameter. Vulval opening circular. Post-uterine sac 33–51 µm long, more than one vulval diameter long, sometimes filled with sperm. Vulva-anus distance 6.4–7.0 times vulval body diameter. Phasmids located at about 1.7–2.2 anal body diameter posterior to anus. Tail long, filiform 1.7–2.2 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 distally followed by single row proximally. Vas deferens a long tube containing spermatocytes transforming into sperm, tapering to an ejaculatory duct. Spicules paired, ventrally strongly arcuate, 1.3–1.4 times cloacal body diameter long. Manubrium oval, calamus/ lamina complex smoothly tapered to a curved distal end. Gubernaculum globose, 45–50% of spicule length, proximal part serrated, caudally projected keel-like with pointed distal tip. Tail divisible into two parts, a short conoid part and a longer filamentous part. Genital sensilla eight pairs; three precloacal and five postcloacal pairs. Genital sensilla in configuration v1, v2d, v3 / v4, ad, ph, (v5, v6), pd. Precloacal pair v1 located anterior to the spicule range, almost one cloacal body diameter anterior to cloaca; v3 just anterior to cloaca; v2d slightly anterior to v3; v4 more than one cloacal body diameter posterior to cloaca and slightly anterior to ad; v5, v6 posterior to ad, v7 absent. Phasmids pore-like, 1.8–2.3 anal body diameter posterior to cloacal opening.

Remarks

The original description of D. graciloides was given by Skwarra (1921) collected from farmyard manure, Kaliningrad, Russia. The morphometric measurements of D. graciloides of our sample concur well with that of Skwarra (1921). However, minor differences were observed in body size (L = 769–865 µm vs 1000–1670 µm in females; 699–857 µm vs 860–1220 µm in males), position of amphids (just posterior to the base of stoma vs far posterior to the base of stoma) and shape of spicules (distally curved vs not curved).

Our population of Diplogastrellus graciloides shows resemblance with its closely related species D. gracilis . However, it differs in having longer tail (c = 2.6–3.1 vs 3.5–3.8 in females; 2.7–3.1 vs 5.3–7.6 in males), position of amphids (at the base of cheilostom vs posterior to the base of stoma), post-uterine sac (present vs absent), size and shape of spicules (19–20 µm; strongly arcuate, smoothly tapered to a curved distal end vs 50–57 µm; long, thin, slender, attenuated to a pointed distal end), size and shape of gubernaculum (9–10 µm; globose with pointed distal tip vs 20–25 µm; keel-like proximal end with a distal sleeve).