Diplogastrellus monhysteroides ( Bütschli, 1874 )

Diplogastrellus monhysteroides ( Bütschli, 1874) View in CoL

Figs 14–19 View Fig View Fig View Fig View Fig View Fig View Fig ; Tables 6–8 View Table 6 View Table 7 View Table 8

Diplogaster minor Goodey, 1929: 27–62 View in CoL , figs 36–37.

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

Emended diagnosis

Diplogastrellus monhysteroides is characterised by a broad stoma longer than wide; elliptical amphidial aperture, at the base of stoma; strong, dagger-like dorsal tooth, anteriorly-directed and small tooth on both subventral walls; pharynx well-developed, muscular ovoid metacorpal bulb with valve plates, narrow isthmus and an oval basal bulb; mono-prodelphic reproductive system with a post-uterine sac; spicules slender with rounded manubrium, strongly arcuate to a curved and pointed distal end; shoe-like gubernaculum, distal end with a rectangular sleeve and nine pairs of genital sensilla.

Material examined

INDIA • 10 ♀♀, 10 ♂♂; Uttar Pradesh, District Bulandshahr ; 28°16′22″ N, 78°1′29″ E; extracted from farmyard manure; slide reference number AMU/ZD/NC/ Diplogastrellus monhysteroides / 1–10 GoogleMaps .

Description

Adult

Body slender, medium-sized, less than 1 mm long; almost straight after fixation, tapering at both extremities. Cuticle with fine transverse striations, longitudinal ridges faint. Lip region round, continuous with body contour. Lips six, amalgamated, each bearing a setose papilla. Amphidial apertures oval, 7–9 µm from anterior end of stoma, at the base of dorsal tooth. Stoma broad, 9–11 µm long. 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 strong, dagger-like, anteriorly-directed tooth, 3–4 µm long; subventral walls provided with small tooth each. Pharynx with slender 54–62 µm long, muscular corpus of uniform diameter; median bulb set off from corpus, ovoid, 15–16 µm long with strong valve plates. Isthmus 29–37 µm long, narrow, conspicuously differentiated from median bulb. Basal bulb oval, glandular, 13–16 ×11–14 µm, only slightly expanded from isthmus without any valve plate or grinder. Nerve ring encircling isthmus in anterior half, located at 69–72% pharyngeal length. Excretory pore and hemizonid not visible. Cardia well-developed, 5–6 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, 5–7 µm without any bacterial pouch. Rectum 1.4–1.7 times anal body diameter long, three rectal glands, one dorsal and two subventral, observed at intestine–rectum junction

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, with distinctly narrower walls, containing sperm. Uterus divisible into a distal small muscular 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, 11–14 µm long about one-third of corresponding body diameter. Vulval opening circular. Post-uterine sac 27–40 µm long, sometimes filled with sperm. Vulva-anus distance 4.1–5.2 times vulval body diameter. Phasmids located at 1.3–1.8 anal body diameter posterior to anus. Tail long, filiform 2.7–3.6 times vulva-anus distance.

Male

Similar to females in general morphology but smaller in size. Anterior region with four cephalic papillae present posterior to circlet of six labial papillae. Reproductive system monorchic, testis reflexed ventrally, 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 paired, slender, ventrally arcuate, 1.7–1.8 times cloacal body diameter long. Manubrium rounded, calamus / lamina complex slightly expanded and smoothly tapering to pointed and curved distal tips. Gubernaculum shoe-like, 45–52% of spicule length, proximally pointed and arcuate, distal end provided with a large rectangular 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, v2, v3d / v4, ad, (v5, v6, v7), phasmids, pd. Precloacal pair v1 located anterior to the spicular range, more than one cloacal body diameter anterior to cloaca; v2 at the level of the spicule head; v3d about one cloacal body diameter anterior to cloaca; v4 just posterior to cloacal aperture; v5–7 clusters greatly separated from each other with left subventral group at the level of ad and right subventral group just anterior to pd. Phasmids pore-like, slightly posterior to left subventral v5–v7 group, 1.3–1.8 anal body diameter posterior to cloacal opening.

Remarks

The original description of D. monhysteroides was given by Bütschli (1874). The values of morphometric characters of D. monhysteroides of our sample overlap with those of Bütschli (1874). Our population also resembles the type population in the shape of lip region, structure of stoma, pharynx, position of nerve ring and shape and size of gubernaculum. However, it differs in shape of spicules and number and arrangement of genital papillae. Spicules in our specimen bear curved distal end ( Fig. 14I View Fig ) while in the type population, they are smoothly arcuate with straight distal end. Bütschli (1874) mentions 12 pairs of genital papillae in which group v5–7 was in two pairs. Both clusters of first pair are situated at the level of ad and both clusters of second pair just anterior to pd while in our population, only one pair of v5–7 is evident. As clearly seen in the SEM images ( Fig. 16F, H View Fig ), the two clusters are separated from each other. The discrepancy in numbers (12 pairs vs 9 pairs) appears to have arisen because of the anteriorposterior segregation of the cluster of v5–7 group which may have resulted in the unusual configuration of the genital sensilla in the type population.

Our population of D. monhysteroides resembles the closely related species D. cerea . However, it differs in position of amphids (at the base of dorsal tooth vs at the level of gymnostom), size of dorsal tooth (dagger-like vs medium-sized), subventral armature (small tooth on both walls vs small ridges on both walls), post-uterine sac (longer than vulval body diameter vs shorter than vulval body diameter), shape of spicules (curved distal end vs smoothly tapering to a distal end), shape of gubernaculum (shoe-like with rectangular sleeve vs keel-like, proximally notched without distal sleeve) and arrangement of genital sensilla (v1 and v2 closely placed; both cluster of v5–7 at the same level vs v2 far posterior to v1, situated near cloaca; v5–7 separated, first pair at the level of ad and second pair just anterior to pd).

Bionomics

The nineteen species of Diplogastrellus are distributed worldwide. Seven species have been recorded from Asia, six from Europe, three from North America, two from Oceania, and one from Africa. Most species, e.g., D. didelphis sp. nov., D. indicus , D. latigubernacula , D. longipharyngis sp. nov., D. robustus sp. nov., D. sikorai , and D. thoubalicus , have been described from India, whereas D. gracilis , D. monhysteroides , and D. stammeri have been reported from Germany, and D. cerea , D. metamasius , and D. prodelphis from the USA. The rest of the species, viz., D. graciloides , D. mikuschi , D. secundus , D. heynsi , D. parvus , and D. pulcher , were described from Russia, The Netherlands, Denmark, South Africa, Fiji, and New Guinea, respectively. The species of Diplogastrellus have been predominantly reported from farmyard manure, rotting banana rhizome, decaying cactus, decay leaves of Iris L., rotting barks, wet humus, soil, compost of mushroom as well as from frass of beetle. However, two species ( D. metamasius and D. monhysteroides ) were reported to be associated with insects. Diplogastrellus metamasius was phoretically associated with sugarcane weevil (Metamasius hemipterus ), recovered as dauer from the abdominal intersegmental folds and grown on xenic culture of bacteria. Diplogastrellus monhysteroides isolated from genitalia of male and female beetles ( Onthophagus taurus ).