Stilestrongylus Freitas, Lent & Almeida, 1937

Digiani, María Celina & Serrano, Paula Carolina, 2024, Synonymy, redescription, molecular characterisation, and new distribution data of species of Stilestrongylus and Guerrerostrongylus (Nematoda, Heligmonellidae) parasitic in sigmodontine rodents from Argentina and Uruguay: a collection-based survey, Zoosystematics and Evolution 100 (4), pp. 1315-1331 : 1315-1331

publication ID	https://doi.org/ 10.3897/zse.100.125466
publication LSID	lsid:zoobank.org:pub:DE37DFA9-F0D9-41AD-B021-7F990C241FA3
DOI	https://doi.org/10.5281/zenodo.13834231
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scientific name	Stilestrongylus Freitas, Lent & Almeida, 1937
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Genus Stilestrongylus Freitas, Lent & Almeida, 1937

Figs 1 View Figure 1 , 2 View Figure 2 , Table 4 View Table 4

Stilestrongylus azarai Durette-Desset & Sutton, 1985

Redescription.

Based on type material (see Material and Methods) and 27 voucher specimens from the same sampling event (14 males, 13 females).

General. Worms small to medium-sized, varying from loosely to tightly coiled, usually with 2–3 spires in anterior portion of body.

Head. Observed in two voucher specimens. Rounded buccal opening surrounded by thin ring; 2 amphids; 4 externo-labial (2 dorsal, 2 ventral); and 4 cephalic papillae visible; lateral externo-labial papillae probably fused with amphids; each cephalic papilla connected with its contiguous externo-labial papilla by thickening, shaped as arc of circle (see description in Digiani and Durette-Desset 2003 c).

Synlophe. Studied in 1 male and 1 female. Identical to that illustrated by Durette-Desset and Sutton (1985). With 25 subequal ridges in both sexes. Double axis of orientation of ridges: right axis inclined at 60 ° to sagittal axis, left axis at 80 °. Twelve dorsal and 13 ventral ridges with respect to axis of orientation (Fig. 1 A, B View Figure 1 ).

Males. Measurements in Table 4 View Table 4 . Bursa large, bell-shaped, and dissymmetrical, with dorsal lobe well developed and right lobe markedly larger than left one. Prebursal papillae not observed. Bursa characterised by papillae 2 (ventral) very close (45–50 μm) to each other (Fig. 1 C View Figure 1 ), implying that lobes were studied separately because spreading out the bursa would break them. Right lobe (Fig. 1 D View Figure 1 ): pattern of type 1-4, with ray 2 arising first from long common trunk of rays 3–6. Ray 3 arising at mid-length of common trunk, but distance between papillae 2 and 3 larger than that between papillae 3 and 4. Rays 4–6 diverging nearly at same level at distal quarter of common trunk, forming the characteristic “ lateral trident ”. Ray 6 curved posteriorly, may be slightly longer than rays 4 and 5. Rays 3, 4, 5, and 6 reaching bursal margin. Left lobe (Fig. 1 E View Figure 1 ): pattern of type 2-2 - 1. Rays 2 and 3 diverging in ‟ V ” proximally. Very short common trunk of rays 4–6, with rays 3 and 6 diverging at same level. Rays 4 and 5 diverging last. All rays reach bursal margin. Distance between papillae 2 and 3 slightly larger than that between papillae 5 and 6. Papillae 3, 4, and 5 approximately equidistant from each other. Rays 2 thickest and 6 thinnest. Dorsal lobe well developed, displaced to the left, compensating the reduced size of left lobe. Dorsal ray very long, divided at about its distal quarter into two branches, each one bifurcated distally into two papillae, external rays 9 and internal rays 10. Arising and path of rays 8 markedly dissymmetrical (Fig. 1 F View Figure 1 ). Left ray 8 arising proximally from dorsal ray, nearly at its base; then running close and parallel to left trunk, approaching to and ending near left papilla 6. Right ray 8 arising more distally on dorsal ray, at about its proximal quarter, running between right trunk and dorsal ray, then heading distally towards right ray 6 but ending far from it. Genital cone long, well developed, bulbous at base, strongly curved ventrally in distal part. Distal half of cone with sclerotised walls. Dorsal lip bearing two rounded conspicuous papillae 7; ventral lip with single lappet-shaped papilla 0 (Fig. 1 G View Figure 1 ). Gubernaculum conspicuous. Spicules thin and alate, ending in single sharp tip.

Females. Measurements in Table 4 View Table 4 . Reproductive tract monodelphic. Uterus less than 20 % of body length; eggs few (3–9). Infundibulum slightly longer than vestibule. Posterior extremity straight or barely curved. Slight cuticular inflation from level of distal uterus up to vulvar aperture. Tail short and stout, ending in mucron (Figs 2 A, B View Figure 2 ). Posterior end moderately retractile.

Voucher material examined.

Argentina • 2 ♂♂, 2 ♀♀; Buenos Aires Province, Balcarce ; 1977–1978; Sutton leg.; Akodon azarae ; MLP-He 0674-1 • 3 ♂♂; same collection data as for preceding; MLP-He 0675-1 • 1 ♂, 1 ♀; same collection data as for preceding; MLP-He 0676-1 • 5 ♂♂, 6 ♀♀; same collection data as for preceding; MLP-He 0683-1 • 3 ♂♂, 4 ♀♀; same collection data as for preceding; MLP 0686-1 View Materials .

Prevalence and mean intensity.

P = 100 % (n = 6), MI = 42.8 (range 5–187) (Table 1 View Table 1 ).

Remarks.

Worms of the type series showed strong contraction and curvature of the anterior body (Fig. 2 C View Figure 2 ). Indeed, the body portion between the cephalic vesicle and the oesophageal-intestinal junction often appeared considerably wrinkled, hindering measurements of soft organs in this region (Table 4 View Table 4 ). On the contrary, the posterior body was relaxed, stretched, and easily accessible for measurements. The scarcity of material led us to include additional specimens from other A. azarae hosts collected in the same sampling event. We examined a total of five complete helminth sets, all of which were composed of worms assignable to S. azarai . Among these, we selected worms with relaxed and stretched anterior ends (Fig. 2 D View Figure 2 ) to take measurements of the proximal part.