Plectus magadani Kuzmin, 1979

Tahseen, Qudsia & Mustaqim, Malka, 2012, Descriptions of six known species of Plectus Bastian, 1865 (Nematoda, Plectida, Plectidae) from India with a discussion on the taxonomy of the genus, Zootaxa 3205, pp. 1-25 : 15-19

Plectus magadani Kuzmin, 1979

( Figs. 9 , 10 )

Measurements: Table 1.

Description. Adult: Body small to medium-sized, curved upon fixation, almost ‘C’-shaped, tapering towards posterior end. Cuticle 1.0–1.5 µm thick; outer cuticle with fine striations nearly indiscernible in LM, inner cuticle smooth. Somatic setae very few and sparse; 3 pairs in cervical region, projecting perpendicular to body surface. Lip region slightly elevated, continuous with adjoining body. Lips amalgamated; inner labial sensilla inconspicuous, outer labials papilliform not distinct in LM. Cephalic sensilla setose, 3 µm long, anteriorly directed, parallel to longitudinal body axis. Amphidial fovea ovoid with prominent ductus amphidialis, about 3 µm in diameter, located at 11 µm from anterior end. Stoma plectoid-type, tubular. Cheilostom weakly cuticularised, arched; gymnostom longer, cuticularised, slightly arched. Stegostom tapering posteriorly, broader at the anterior end, gradually narrowing towards base. Pharynx comprising of a cylindrical corpus continuous with isthmus. Basal bulb elongate to ovoid, moderately muscular, 20x15 µm in dimension having a parietinus -like grinder with six pairs of denticulate ridges; post-bulbar extension offset from basal bulb, 8 µm long. Cardia inconspicuously separated from post-bulbar extension. Body at pharyngeal end ca 2.5 times lip diameters wide. Nerve ring located at about 53% of pharyngeal length. Secretory-excretory pore posterior to nerve ring or at about 59% of pharyngeal length with the duct forming a single loop before joining the renette cell. Intestine transparent, with wide lumen. A pair of oval- shaped pseudocoelomocytes of slightly less than corresponding body diameter in length, present posterior to cardia. Rectum with heavily cuticularised walls, 0.9 times anal body diameter long. Anus a crescent-shaped slit.

Female: Reproductive system didelphic, amphidelphic, ovaries reflexed antidromously on the dorsal side. Spermatheca absent; crustaformeria not distinguishable. Vagina ca 1/3rd of corresponding body diameter in length with folded inner walls forming epiptygmata; two pairs of sphincter muscles. Vulva nearly equatorial, vulval lips slightly protruded. Vulva-anus distance 215 µm. Tail 68 µm long, curved, about 5 times as long as the anal body diameter or 32% of vulva-anus distance. Caudal setae three pairs including two subdorsal pairs and one lateral pair pointing downward. Terminal seta 10 µm anterior to tail terminus. Three linearly arranged caudal glands opening to exterior through 2 µm long spinneret; setose papillae surround the spinneret.

Male: not found.

Locality and habitat. A sample containing Plectus magadani was collected from a drain at Nainital, Uttaranchal, India.

Voucher specimens. One female on slide Plectus magadani Kuzmin, 1979 NON/ 1–6 deposited in the Nematode Collection, Department of Zoology, Aligarh Muslim University, Aligarh, Uttar Pradesh, India. [One female was used for SEM study].

Salient characters. A small species with narrow but continuous lip region; lips with simple, smooth inner ends; cephalic setae anteriorly directed, parallel to main body axis; amphidial fovea circular, at middle or posterior to middle level of stoma; secretory-excretory duct conspicuous with turns, pharyngeal bulb weak with parietinus - like grinder, vagina with epiptygmata and two pairs of sphincter muscles; tail spinneret surrounded by small papillae.

Remarks. P. magadani has been reported from Africa ( Egypt, Nigeria, Zaire, South Africa) and Europe ( Bulgaria, Czech Republic, Finland, Hungary, Poland, Romania, Russia, Spain). In the present paper, the two specimens, the first report of the species from India, show conformity to P. magadani in all morphological and morphometric characteristics (apud Zell, 1993) except the setose papillae surrounding spinneret observed by Scanning Electron Microscope which are obviously not discernible in LM.

Plectus communis B ü tschli, 1873 ( Figs. 11 , 12 )

Measurements: Table 1.

Description. Adult: Body slender, small to medium-sized, slightly arcuate upon fixation, tapering towards extremities, more towards the posterior end. Cuticle 0.8–1.2 µm thick; outer and inner cuticles finely striated. Somatic setae sparse, cervical setae 4 pairs, projecting perpendicular to body surface. Lip region slightly elevated to truncate, continuous with adjoining body. Lips amalgamated; inner labial sensilla inconspicuous, outer labials papilliform not discernible in LM. Cephalic sensilla setose, 3 µm long, directed anteriorly, parallel to main body axis. Amphidial fovea circular, 3 µm in diameter, located at 10 µm from anterior end. Stoma plectoid type, tubular. Cheilostom weakly cuticularised, with posteriorly converging walls; gymnostom parallel-walled, cuticularised. Stegostom slightly tapering with abrupt narrowing at base. Pharynx comprising of a cylindrical corpus continuous with isthmus. Basal bulb elongate to ovoid, moderately muscular, 20x15 µm in dimension having a valvular apparatus with six pairs of denticulate ridges; post-bulbar extension 10 µm long. Cardia inconspicuously separated from post-bulbar extension. Body at pharyngeal end ca 2.5 times lip diameters wide. Nerve ring encircling pharynx at 53% of pharyngeal length. Secretory-excretory pore slightly posterior to nerve ring, at 59% of pharyngeal length with the duct forming two loops before joining the renette cell. Intestine with wide lumen. The rectum is 20 µm long.. A pair of oval shaped pseudocoelomocytes ca 0.7 times corresponding body diameter long, located posterior to cardia. Rectum thin-walled, 0.8–0.9 times anal body diameter long. Anus a crescent-shaped slit.

Female: Reproductive system didelphic, amphidelphic; ovaries reflexed antidromously on the dorsal side. Anterior ovary on the left and posterior on the right side of intestine. Spermatheca absent; crustaformeria prominent. Vagina anteriorly directed, ca 30% of corresponding body diameter in length with folded inner walls forming a weak epiptygmata; provided with two pairs of sphincter muscles. Vulva nearly equatorial transverse slit, vulval lips not protruded. Vulva-anus distance 200 µm. Tail long, largely straight to slightly curved, ca 31% of vulva-anus distance long. Caudal setae five including one subventral pair and one lateral pair, pointing downward. Terminal seta 15 µm anterior to tail terminus. Three linearly arranged caudal glands opening to exterior through 2 µm long spinneret without any surrounding papilla.

Male: Not found.

Locality and habitat. A sample containing Plectus communis was collected from a small ditch at Nainital, Uttaranchal, India.

Voucher specimens. One female on slide Plectus communis Bütschli, 1873 NON1/ 1 deposited in the Nematode Collection, Department of Zoology, Aligarh Muslim University, Aligarh, Uttar Pradesh, India. [One female was used for SEM study].

Salient characters. A small, species with conspicuous cuticular striations; continuous, slightly elevated lip region; lips with simple, smooth inner ends; cephalic setae anteriorly directed, parallel to main body axis; amphidial fovea circular, at middle level of stoma; secretory-excretory duct conspicuous with turns, pharyngeal bulb weak with parietinus-like grinder, vagina with epiptygmata and two pairs of sphincter muscles, tail spinneret simple.

Remarks. The present population of P. communis , reported for the first time from India, conforms to previously described populations of P. communis in most morphological and morphometric characteristics. However, some minor differences were observed viz., absence of males [vs males reported in P. c om m u ni s apud Zell, (1993)].

Figures

FIGURE 9. Plectus magadani Kuzmin, 1979. A: Female, entire. B: Anterior end. C: Pharyngeal region. D: Female reproductive system. E: Caudal region.

FIGURE 10. Plectus magadani Kuzmin, 1979. A: En face view. B – E: Anterior end. F: Body region showing corpus-isthmus. G: Body region showing posterior pharynx. H: Body region showing lateral alae. I: Female reproductive system. J, K: Caudal region. L: Tail terminus (Scale bar = 5 µm).

FIGURE 11. Plectus communis Butschli, 1873. A: Female, entire. B: Anterior end. C: Pharyngeal region. D: Female reproductive system. E: Caudal region.

FIGURE 12. Plectus communis Butschli, 1873. A – D: Anterior end. E, F: Body region showing posterior pharynx. G, H: Body region showing lateral alae. I: Female reproductive system. J, K: Caudal region. L: Tail terminus (Scale bar = 5 µm).