Pomponema proximamphidum, Tchesunov, Alexei V., 2008

Tchesunov, Alexei V., 2008, Three new species of free­living nematodes from the South­East Atlantic Abyss (DIVA I Expedition) *, Zootaxa 1866, pp. 151-174 : 163-169

Pomponema proximamphidum sp. nov.

Figs 7–9

Type material: Holotype male N1, two paratype males NN2 & 3 mounted in glycerin on glass slides. Type specimens are deposited in the DIVA nematode collection.

Type locality: DIVA I, Meteor 48/1, Station 346/2, Multicorer 3: South­east Atlantic Ocean, 16°17.0'S & 005°27.0'E, depth 5389 m. 27 July 2000.

Etymology: The species name reflects the position of amphids close to the labial position.

Morphometric data: Table 3.

Description. Body cylindrical, slender. Cuticle annulated and punctated with dots. Cuticle heterogeneous: thick, light­refracting, brownish in colour cuticle with sharp annules in the anterior body while thinner, lighter in colour cuticle with less sharply defined annules from about 0.4 pharynx length onwards. Anterior end characterized by large, distinct dots arranged in regular transversal rows becoming smaller towards the midpharynx and fusing thereafter into transversal lines. Lateral differentiations of the body cuticle begin just posterior to the amphidial fovea. Lateral differentiation expressed in a pattern of a sequence of paired big light­refractive dots sharply set off other lateromedian dots of the respective transversal row. The big dots in pairs joined by narrow dots. Space between big lateral dots about 7 µ m at the level of the nerve ring and 4 µ m on the midbody.

TABLE 3. Morphometry of Pomponema sp. nov.

Character Specimens & labels

1 (holotype)* 2 (paratype) 3 (paratype)

Box A N3(7) Box A N9(3) Box A N9(4)

DIVA I, M 48/1, DIVA I, M 48/1, DIVA I, M 48/1,

346/2, MuC3 346/2, MuC3 346/2, MuC3 *The specimen was slightly flattened while being measured. **Anteriormost – posteriormost supplement

***lateral + lateromedian sensilla

Inner labial sensilla indistinct. Outer labial and cephalic sensilla constitute together a common circle. Six outer labial setae differ notably to one another: lateral setae much shorter than lateromedian outer labial setae. Four cephalic setae a little shorter than the outer labial lateromedian setae. Cervical and somatic setae not found. There are few fuzzy cuticular pores in the pharyngeal region and no visible pores farther posteriad. Amphidial fovea very large multispiral groove, ventrally coiled, with about five turns. It is half shifted to the apical surface of the head.

Buccal cavity differentiated into two compartments. Cheilostoma shaped as a truncate cone; its walls armoured with twelve stick­like ternary (three­storyed) rugae. Stegostoma provided with a big and acute dorsal tooth as well as two smaller subventral acute teeth. At the level of each side of the subventral teeth, a lateroventral row of six to eight tiny two­storyed dentlicles.

Pharynx evenly muscular throughout its length, slightly widening posteriorly but not forming a well defined bulb. Nerve ring well visible at the midpharynx. Terminal ampulla of the dorsal pharyngeal gland discernible at the base of the dorsal tooth. Cardia indistinct. There are rather large swallowed particles inside the intestine lumen.

Renette ampulla transparent and voluminous; ventral pore situated at a distance of about one third pharynx length from the anterior end.

Reproductive system diorchic. Both anterior outstretched and posterior reflected testes situated to the left of the intestine in all the specimens. Vas deferens consists of several parts (from anterior end caudad): medium granulated, finely granulated, homogeneous, and coarsely granulated.

Spicules short, arched, distally pointed and proximally widened. Gubernaculum as paired slightly curved plate distally adjoined to spicules. There is a small funnel­like structure with an indented sclerotized rim at each lateral side of the spicule distal tip.

Thirteen to fourteen midventral preanal supplementary organs. Each organ consists of a stout cylindrical body and a flat cover with a central opening. The supplementary organs may or may not be elevated above the body cuticle depending on the body curvature. There a small midventral sensilla just anterior to the cloacal opening.

Tail relatively long, consisting of proximal conical and slender cylindrical parts. A short terminal spinneret tube at the tail end. There are a few small setae laterally on the conical part.

Diagnosis. Male body length 911–1203 µ m. Cuticle heterogeneous: anteriormost cuticle thicker, brownish, with sharp annules in the anterior body while more posterior cuticle thinner, light, with less sharply defined annules. Lateral differentiation expressed in a pattern of a sequence of paired light­refractive dots sharply set off other much smaller lateromedian dots. Inner labial sensilla as conical papillae. Six outer labial sensilla differ notably to one another: labial sensilla as minute setae much shorter than lateromedian sensilla looking like true short setae. Four cephalic setae a little shorter than outer labial lateromedian setae. Amphidial fovea very large, multispiral, with about five turns; half shifted to the apical surface of the head. Stegostoma armoured by a big acute dorsal tooth, two smaller subventral acute teeth and two lateroventral rows of denticles at the level of the subventral teeth. Ventral pore situated at a distance of about one third pharynx length from the anterior end. Diorchic, posterior testis reflexed. Spicules short, arched, distally pointed and proximally widened. Gubernaculum as paired slightly curved plate with a small funnel­like structure with an indented sclerotized rim at each lateral side of the spicule distal tip. Thirteen to fourteen midventral preanal supplementary organs. Tail length 7.45–8.12 anal diameters; its distal cylindrical part 52–62% of the entire tail.

Differential diagnosis: P. proximamphidum sp. nov. share the subapical position of the amphidial fovea and distinct lateral differentiation of the somatic cuticle with five other species: P. concinnum Wieser, 1954 , P. corniculata Gourbault, 1980 , P. mirabile Cobb, 1917 , P. multipapillatum Filipjev, 1922 and P. stomachor Wieser, 1954 .

P. proximamphidum sp. nov. differs from P. concinnum ( Chile, 70–80 m) with the index c’ (7.45–8.12 versus 6), longer posterior cylindrical part of the tail (52–62% versus 41%), relative width of the amphidial fovea (55–59% c.b.d. versus 40% c.b.d.), lesser number of supplementary organs (13–14 versus 20).

P. proximamphidum sp. nov. differs from P. corniculata , a geographically close species ( Angola Basin, 2063–3615 m) with much longer tail (index c 4.00–6.03 versus 11.4–13.5 and c’ 7.45–8.12 versus 2.3–2.5) with longer posterior cylindrical part of the tail (52–62% versus 21%), more anterior position of the ventral pore at about half the distance from the cephalic apex to the nerve ring versus just at the nerve ring (54–60 µ m and 105 µ m, respectively), bigger amphidial fovea (width 9–11.5 µ m versus 7 µ m), lesser number of supplementary organs (13–14 versus 20).

The original description of P. m i r a b i l e (no locality indicated by Cobb) misses some significant details and any indication on locality, hence the relation of the new species to P. m i r a b i l e remains unclear. However P. proximamphidum sp. nov. is distinctly separated from P. mirabile in the body length (911–1203 µ m versus>1800 µ m), smooth versus jonted setae of the cephalic ring, smaller amphidial fovea (55–59% c.b.d. versus 93% c.b.d.), lesser number of supplementary organs (13–14 versus 20).

P. multipapillatum is known from two thorough descriptions of Filipjev (1922, Black Sea, sublittoral silt) and Lorenzen (1972, Helgoland in the North Sea, 30–34 m). P. proximamphidum sp. nov. differs from P. multipapillatum with much longer tail (index c 4.00–6.03 versus 7.3–10 and c’ 7.45–8.12 versus 3.7–4.5) with longer posterior cylindrical part of the tail (52–62% versus 28–44%), position of the ventral pore (respectively 54–60 µ m and 15–38 µ m from the cephalic apex to the ventral pore), shorter setae of the cephalic ring (2–4.5 µ m versus 4–8 µ m), lesser number of supplementary organs (13–14 versus 15–19).

P. proximamphidum sp. nov. differs from P. stomachor ( Chile, tidal exposed sand) by smaller body (911– 1203 µ m versus 1950–2170 µ m), longer tail (index c 4–6.03 versus 7.1–8, c’ 7.45–8.12 versus 7), much shorter setae of the cephalic crown (2–5.5 µ m versus 3–18 µ m), smaller amphidial fovea (9–11.5 versus 20 µ m), shorter distance from the cephalic apex to the ventral excretory pore (width 54–60 µ m versus 110–150 µ m), smaller spicules (33–44.5 µ m versus 75 µ m), lesser number of supplementary organs (13–14 versus 15– 19).

Figures

FIGURE 7. Pomponema proximamphidum sp. nov., anterior ends. A: male N 1 (holotype), depicted right row of denticles; B: male N 3 (paratype), surface view; C: male N 3 (paratype), optical section, depicted left row of denticles. Scale bars: 10 µ m.

FIGURE 8. Pomponema proximamphidum sp. nov., details of the holotype male. A: anterior body; B: posterior end; C: copulatory apparatus. Scale bars: A, B 50 µm; C 10 µm.

FIGURE 9. Pomponema proximamphidum sp. nov., details. A: male N 1 (holotype), entire; B: male N 3 (paratype), cloacal region. Scale bars: A 100 µ m; B 10 µ m.