Halicephalobus termitis, Mahboob, M. & Tahseen, Q., 2022

Mahboob, M. & Tahseen, Q., 2022, Description of a new and a known insect-associated species of the genus Halicephalobus Timm, 1956 (Panagrolaimidae: Rhabditida) along with intrageneric relationship, Journal of Natural History 55 (39 - 40), pp. 2549-2567 : 2551-2556

Halicephalobus termitis sp. nov.

( Figures 2 (a-e), 3 (a-h), 4 (a-h), 7, 8)

Measurements

See Table 1 .

Description

Female

Body small,stout,tapering at both extremities and slightly curved at ventral side upon fixation. Cuticle 0.5 μm thick at mid-body, cuticle finely striated. Lateral field with two ridges occupying 18–20% of mid-body diameter, extending from metacorpus to the phasmids and single ridge extending beyond the phasmids. Lip region wider than high, slightly offset from adjoining body. Cephalic plates sclerotised. Lips small, six in number, well separated; each lip with a minute labial sensilla, not discernible under LM. Amphids labial with round to elliptical opening. Oral aperture hexagonal, six lips, separated. Stoma well developed, 8–9 μm long or 13.1–13.2% of total pharyngeal length, divided into distinct cheilo-, gymno- and stegostom. Cheilostom weakly cuticularised, nearly as long as wide. Gymnostom longer than cheilostom with highly cuticularised parallel walls, about 2 times longer than wide. Stegostom slightly narrower than gymnostom, with pro-meso- and metastegostom distinct on ventral side. Dorsal wall of metastegostom conically projected inward without discernible tooth, telostegostom narrowing in to pharyngeal lumen.Pharynx well developed,about 24.2–28.9% of total body length, divided into long, slender 24–29 μm longer corpus, a swollen, highly muscular metacorpus of 10–12 μm × 8–9 μm in dimension, a narrow, 13–20 μm long isthmus and slightly rounded, highly muscular, well-developed basal bulb of 11–14 μm × 11–13 μm in dimension, having a grinder and haustrulum. Cardia conoid, 2–3 μm long. Nerve ring surrounding posterior region of isthmus at ca 68.2–77.0% of total pharyngeal length from anterior end. Secretory–excretory duct opening just posterior to nerve ring or ca 57–65% of pharyngeal length. Deirids indistinct. Intestine with wide lumen, thin-walled; intestinal cells and nuclei not discernible. Rectum about as long as anal body diameter. Reproductive system monodelphic;ovary with double flexures extending beyond vulva.First flexure 56–73 μm long while next flexure dorsal, 17–32 μm long or 1/3 of anterior ovary with oocytes arranged in 2–3 rows followed by oocytes arranged in single row proximally. Oviduct and spermatheca not conspicuously separated.Uterus about twice corresponding body diameter long. Post-uterine sac absent. Vagina oblique with thick walls, constituting 27.8–47.4% of corresponding body diameter. Vulva far posterior in position, ca 71.2–74.9% of total body length. Vulva slit-like opening surrounded by protruded lips. Vulva–anus distance 55–68 μm or about twice tail length.Tail short, conical,possessing three prominent caudal cells present in the caudal region resembling caudal glands without any discernible terminal duct or opening; a minute cuticularised terminal mucro present. Phasmids located at mid-level of tail.

Male

Not found.

Dauer/phoretic juveniles

Body smaller, slightly ventrally arcuate upon fixation. Cuticle smooth, thin, ca 0.1–0.2 μm. Lateral field with single ridge. Lip region twice its height, continuous with body contour. Stoma long, narrow, ca 5–6 times longer than wide. Pharynx well developed with slender, 16–19 μm long procorpus, with metacorpus swelling of 6–8 μm × 4–67 μm in dimension and a much narrower, 13–14 μm long isthmus, expanded posteriorly into an ovoid basal bulb of about 7–8 μm × 56 μm in dimension. Nerve ring encircling mid-region of isthmus. Secretory–excretory duct inconspicuous, occasionally seen just behind nerve ring. Cardia short, conoid. Intestine thick-walled, granular. Rectum about as long as anal body diameter. Tail short, conical, ending with sharp pointed tip.

The dauer larvae were isolated from the head of excised adult Rhinotermes lucifugus , while other life stages of nematodes could be found on the termite mound and adjoining rotting wood. The nematodes were cultured on NGM seeded with bacteria. No males could be found in the culture, indicating parthenogenesis was the only mode of reproduction.

Type habitat and locality

Halicephalobus termitis sp. nov. was isolated from the head of Rhinotermes lucifugus and collected from the termite mound in the hollow of a Pongamia pinnata (Fabaceae) tree (commonly known as Karanj) from Aligarh Fort, Uttar Pradesh, India, at coordinates 27.5534° N 78.0429°E

Type material

Twelve females (the holotype and 11 paratypes) of Halicephalobus termitis sp. nov. on slides Q1/1-8 were deposited in the Nematodes Collection, Department of Zoology, Aligarh Muslim University, Aligarh, Uttar Pradesh, India. Two paratype females were deposited in the Nematode Collection Unit, Indian Agricultural Research Institute, Pusa, New Delhi.

Diagnosis and relationships

Halicephalobus termitis sp. nov. is characterised by small body size; lateral field with two ridges terminating into one ridge posterior to phasmids;lips small,arranged around a hexagonal oral aperture; stoma with weakly cuticularised cheilostom; longer strongly cuticularised gymnostom; dorsal wall of metastegostom conically projected without a discernible tooth; secretory– excretory pore located at level of basal bulb; ovary with double flexures with posterior dorsal flexure about 1/3 of anterior flexure and the distal tip reaching anterior level of vulva; vagina oblique with protruded vulval lips; vulva–anus distance about twice tail length; tail short, conical with three conspicuous caudal cells, tapering into a minute mucro.

Halicephalobus termitis sp. nov. resembles H. similigaster ( Andrássy, 1952) Andrássy, 1974 in most morphological and morphometric characters but differs in having smaller a (10.6–13.2 vs 17.7–25.0) and c’ (2.6–3.2 vs 4.0–10.0) and greater V (71.2–74.9 vs 49.0– 67.6) values; lip region with (vs without) sclerotised cephalic plate; posterior flexure extending anterior to vulva (vs up to or at posterior level of vulva); and tail short conical (vs elongate conoid in H. similigaster apud Andrássy, 1952 ; Körner 1954; Köhler 2011).

The new species differs from H. brevicauda (Mavljano, 1976) Andrássy, 1984 in relatively smaller a (10.6–13.2 vs 13–17) and c (6.6–8.1 vs 11–14) values;lip region offset (vs continuous); shorter stoma (8–9 μm vs 16 μm); nerve ring surrounding posterior region of isthmus (vs anterior region of isthmus); secretory–excretory pore at level of basal bulb (vs at mid-level of isthmus); vulva relatively posterior (V = 71–75 vs 56–60); and anal body diameter (11–13 μm vs 4–11 μm in H. brevicauda apud Andrássy, 1984 ).

Halicephalobus termitis sp. nov. is a plump species that, besides showing a difference in habitat, differs from the closely related H. laticauda Geraert et al., 1988 in its relatively smaller body (211–260 μm vs 255–347 μm); smaller a (10.6–13.2 vs 24–29) and c’ (2.6–3.2 vs 4.1–6.2) values; nerve ring surrounding posterior region of isthmus (vs anterior region of isthmus); secretory–excretory duct opening at level of basal bulb (vs mid-level of isthmus); reproductive system larger, occupying 48–67% (vs 26–33%) of the body; relatively posterior vulva (V = 71–75 vs V = 52–63); eggs wider (35–40 × 15–18 μm vs 40 × 6 μm); tail uniformly tapering (vs abruptly tapering); and tail tip without a sclerotised string (vs sclerotised string present in H. laticauda apud Geraert et al., 1988 ).

The new species differs from H. gingivalis ( Stefanski, 1954) Andrássy, 1974 in its relatively smaller body size (211–260 μm vs 250–430 μm); smaller a (10.6–13.2 vs 15–23) and c’ (2.6–3.2 vs 5.4–5.5) values; vulva situated more posteriorly (V = 71–75 vs 56–65); metastegostom without any discernible tooth (vs with a minute tooth); nerve ring surrounding posterior region of isthmus (vs anterior region of isthmus); secretory–excretory duct opening at level of basal bulb (vs mid-level of isthmus); rectum as long as anal body diameter (vs longer than anal body diameter); and tail short conical (vs long conoid in apud Anderson and Bemrick, 1965).

Halicephalobus termitis sp. nov. differs from H. persicus Shokoohi et al., 2007 in having smaller a (10.6–13.2 vs 21–26) and c’ (2.6–3.2 vs 6.9–12.3) values; greater c (6.6–8.1 vs 4.4–5.2) and V (71–74 vs 54–61) values; stegostom about as wide as gymnostom (vs narrower than gymnostom); nerve ring surrounding posterior region of isthmus (vs anterior region of isthmus); secretory–excretory duct opening at level of basal bulb (vs mid-level of isthmus); and greater vulva–anus distance (55–68 μm vs 43–54 μm in H. persicus apud Shokoohi et al., 2007 ).

The new species differs from H. mephisto Borgonie et al., 2011 in its relatively smaller body (211–260 μm vs 520–560 μm); smaller a (10.6–13.2 vs 32.9–34.6), b (3.5–4.1 vs 5.4–5.6) and c’ (2.6–3.2 vs 9–10) values; greater c (6.6–8.1 vs 4.3–4.7) and V (71–75 vs 53–57) values; gonad with double flexure (vs single flexure); rectum as long as (vs shorter than) anal body diameter; and tail short conical (vs long filliform in H. mephisto apud Borgonie et al., 2011 ).

Etymology

The specific epithet is based on the termite host that yielded the nematodes.

Figures

Figure 2. Halicephalobus termitis sp. nov. female. (a) Entire body; (b) anterior end; (c) pharyngeal region; (d) reproductive system; (e) posterior region.