Syringolaimus elegans, Tchesunov, 2017

Tchesunov, Alexei V., 2017, Free-living nematodes of the genus Syringolaimus de Man, 1888 (Nematoda, Enoplida, Ironidae) from the Angola Basin, South-East Atlantic Abyss, Zootaxa 4306 (4), pp. 478-500 : 494

Syringolaimus elegans sp. n.

( Figures 7–9 )

Material: DIVA 1 , M 48/1, st 325/4, Muc 8. Holotype male and paratype juvenile with vestigial ovaries. The slides are deposited in Senckenberg Museum (Frankfurt am Main, Germany) under the inventory numbers SMF 17055 (holotype) and SMF 17056 (paratype).

Male. Body slender, filiform. Body length 2718 µ m, a=98.8, b=8.47, c=11.8, c’=8.41. Body diameter at the level of: anterior sensilla 17 µ m, nerve ring 34.5 µ m, cardia 35.8 µ m, midbody 27.5 µ m, cloaca 24.1 µ m. Cuticle smooth along the entire body except numerous irregular transversal fissures or chaps like in cervical region. No metanemes found. Anterior sensilla hardly discernible as six papillae or pores. Amphidial aperture a transverse slit; fovea poorly visible. Width of the amphidial aperture 5.9 µ m or 31% of the corresponding body diameter, distance from anterior apex to aperture 11.5 µ m. No somatic sensilla along the body. Apical cuticle around the mouth opening widened and its internal sublayer sclerotized. There are three equal doubled cheilostomatal teeth about 4.6 µ m long. The teeth joined movably to the sclerotization of the internal layer of the apical cuticle. Each tooth consists of two parts (subteeth) fused basally; both parts isomorphic claw-like, one part somewhat bigger than another. Dorsal tooth consists of left bigger and right smaller parts. Pharyngostom 79 µ m long and 3.4 µ m wide, tubular, with sclerotized walls, but flexible. Pharyngostom enveloped by a cuff (manchette) with obliquely directed muscular striation. Pharynx evenly muscular throughout its length, with distinct thick internal cuticular lining. Posterior part of the pharynx slightly enlarged into an elongate ovoid bulb 70 µ m long and 32 µ m wide; however, its internal cuticular lining not modified. Cardia conical, with radial striation. Intestine with glycocalyx layer detached. Nerve ring distinct, at the middle of the pharynx. No clear indication of a ventral gland; however, a ventral pore and a thin intracuticular canal present at a distance of 36 µ m anterior to the nerve ring. Male monorchic, male genital branch 1156 µ m long, situated to the right of the intestine. Spermatozoa (or spermatids?) fiber-like. Vas deferens consists of anterior slender and posterior thicker portions. Spicules slender, arcuate, 32 µ m long, weakly sclerotized, their anterior (proximal) knobs not pronounced (underdeveloped?). Gubernaculum vestigial, hardly visible. There is one midventral precloacal supplementary papillum with a thin internal canal located at a distance of 8 µ m anterior to the cloacal opening; two other supplements situated a bit closer to the cloaca, are questionable and may actually represent cuticular folds. No other sensilla in pericloacal region. Tail long, its proximal conical part gradually transforms to thin whip-like part constituting about 67% of the total tail length. No indication of spinneret and caudal glands.

IV juvenile stage (slightly compressed). Body length 2786 µ m, a=68.0, b=8.55, c=11.9, c'=8.1. Body diameter at the level of: anterior sensilla 12 µ m, nerve ring 38 µ m, cardia 51 µ m, midbody 48 µ m, cloaca 30 µ m. Width of the amphidial aperture 3.5 µ m or 24% of the corresponding body diameter, distance from anterior apex to aperture 9.3 µ m. Buccal cavity 61 µ m long. Replacing teeth present just posterior to the functional teeth. Terminal bulb 60 µ m. Vestigial female branches present but no vagina could be found. Posterior cylindrical portion of the tail 69% of the total tail length.

Diagnosis. Body length of male 2718 µ m, a=98.8, b=8.5, c=11.8, c'=8.4. Distance from head apex to the amphidial aperture 11.5 µ m. Buccal cavity 79 µ m. Basal pharyngeal bulb 70 µ m long and 32 µ m wide. No ventral gland. Monorchic with single anterior outstretched testis. Spicules arcuate, very weak, 32 µ m. A single evident midventral precloacal supplementary organ as a papillum with an axial canal. Tail with cylindrical posterior portion constituting 67% of the entire tail. No evident spinneret and caudal glands.

Differential diagnosis. Syringolaimus elegans sp. n. differs from all other species of Syringolaimus by slimmer body (a 99 vs. 30–73) and from all species except S. ingens by its greater body length (2718 µ m vs. 760– 1750 µ m), longer buccal cavity (79 µ m vs. 28–58 µ m), and longer terminal pharyngeal bulb (70 µ m vs. 29–53 µ m). S. elegans sp. n. differs from S. ingens nom. nud., the largest species within the genus, by smaller and slimmer body (L=2718 µ m versus 3735 µ m, a=99 vs. 43), relatively longer tail (c'=8.4 vs. 4.0), smaller spicules (32 µ m vs. 70 µ m) and by presence of a precloacal supplementary papillum (not mentioned for S. ingens ).

Figures

FIGURE 7. Syringolaimus elegans sp. n., entire. A: holotype male; B: paratype juvenile. Scale bars: A – B = 500 µ m.

FIGURE 8. Syringolaimus elegans sp. n., anterior body. A: holotype male, anterior end; B: juvenile, anterior end. C: holotype male, pharyngeal region. Scale bars: A – B = 20 µ m; C = 100 µ m.

FIGURE 9. Syringolaimus elegans sp. n. posterior body. A: holotype male, tail; B: holotype male, spicules and precloacal region; C: juvenile, tail. Scale bars: A, C = 100 µ m, B = 20 µ m.