Paramelomystrongylus dessetae, Smales, 2020

Durette-Desset, Marie-Claude & Digiani, María Celina, 2023, Revision of the genera of Heligmonellidae (Nematoda, Heligmosomoidea), parasitic in Muridae from New Guinea, Parasite (Paris, France) 30 (63), pp. 1-34 : 28-30

3.11.1 Analysis of data and difficulties encountered Paramelomystrongylus dessetae

3.11.1.1 General

There are two numbering mistakes in [ 43]. In Figure 8 , the reference “D” is employed twice, whereas “G” is absent from the plate (though present in the Captions). We interpret therefore that captions E, F, G (which are successive in the Captions) correspond to body sections D, E and F, which are successive in the plate (proximal, mid-body and distal), respectively. On the other hand, caption “G” refers to a female “posterior section midbody transverse section”. We assume that it concerns a section within the distal part of the body. Due to this labelling confusion of the original, we only use herein our own numbering for the body sections.

3.11.1.2 Synlophe (based on sections from two males and two females)

Sections analyzed herein are those within proximal body: female ( Fig. 11A ), and at midbody: male ( Fig. 11B ) and female ( Fig. 11D ); within distal part of female ( Fig. 11C ). No lateral hypodermal cords shown in any section; ridges numbered in Fig. 11B .

In all sections, careen present supported by two ridges of which ventral one largest. In Figures 11A and 11C ventral ridges exceed edge of external line of cuticle except ridge 2 of Figure 11C which does not reach this latter. From Smales [ 43], the dorsal ridges are continuous, the ventral ones discontinuous, and the axis of orientation is described as subfrontal.

Within proximal body: in Figure 11A (first female section in [ 43]), 16 ridges; ridges irregularly spaced with four gaps: two on left side and two on right side (arrowheads); dorsal ridges medium- to small-sized, oriented from right to left; six ridges grouped mid-ventrally, regularly spaced, subequal and small, oriented from right to left. On right side, two divergent ridges (curved arrows), of which ventral one small.

At midbody: in Figure 11B (male), 16 ridges irregularly spaced with two gaps, one on each side of careen (arrowheads); dorsal and ventral ridges small and regularly spaced, ventral ones more serried than dorsal ones. Ridge 10’ oriented perpendicularly to body surface. Ridges 6 and 9’ oriented in opposite directions (curved arrows).

Figure 11D (second female section in [ 43]): 18 ridges including careen. Presence of 2 large ridges opposite to careen, strongly directed ventrally and clearly diverging with respect to dorsal ridges (curved arrows). Remaining ridges small, regularly spaced, mainly oriented perpendicularly to body surface.

Within distal body: in Figure 11C (third female section in [ 43]), 15 ridges irregularly spaced with two gaps, one on each side of careen (arrowheads); dorsal and ventral ridges regularly spaced, dorsal ridges medium-sized, ventral ridges smaller and more serried than dorsal ones; presence of minute ridge at base of ventral ridge of careen (straight arrow). Opposite to careen, tips of two ridges pointing in opposite directions (curved arrows).

3.11.1.3 Bursa (illustrated in [ 43]: Figs. 8I, 8J, 8K )

Figure 8I , left lobe, orientation not specified, with no link with left ray 8, rays 2-6 illustrated. Figure 8J , dorsal lobe, orientation not specified, with no links to rays 6. Figure 8K , right lobe, orientation not specified, rays 2-6 and right ray 8 illustrated. From the text [ 43], the bursa is dissymmetrical with left lobe larger, dorsal lobe is shorter than lateral ones, pattern of type 2-3.

3.11.2 Comments

3.11.2.1 Synlophe

In all figures, the presence of a careen allows the numbering of the ridges ( Figs. 11A’ and 11C’). The presence of: (1) careen, (2) two groups of ridges (dorsal and ventral) pointing in opposite directions, and (3) right ridges with divergent tips, allow us to determine an axis of orientation that is the same in all sections. In the absence of the lateral cords as a reference, the inclination of this axis with respect to the sagittal axis remains uncertain. For the other characters, three sections are similar: female within proximal body (11A’), male at midbody (11B) and female within distal body (11C’).

In Figure 11D , the two large ridges opposite the careen are considered as right ridges. They are strongly directed ventrally and clearly diverge with respect to the dorsal ridges. This could indicate the start of an oblique axis of orientation, on the right side, inclined from right-dorsal to left-ventral. Such an inclination has never been observed among the Nippostrongylinae , and we propose that Figure 11D be slightly rotated clockwise so that this axis becomes perpendicular to the sagittal axis ( Fig. 11D’ ). However, on the left side the careen is determining another axis with a different inclination, oblique from right-ventral to left-dorsal side. The result is a double axis whose inclination has never been observed because usually, among the Nippostrongylinae , the left axis is more inclined on the sagittal axis that the right one. In addition, the orientation of the remaining ridges is uncertain.

Under Paramelomystrongylus we are in the presence of two types of synlophe sharing the presence of a large careen:

Type I (11A–11C’) with careen plus 14 ridges at midbody probably in both sexes; ridges (excluding careen) medium-sized to small, irregularly spaced, with many gaps and 2 medium-sized right ridges with divergent tips. Axis of orientation probably subfrontal.

Type II (11D/11D’), with careen plus 16 ridges within proximal body in female (unknown in male). Ridges (excluding careen) small, subequal and regularly spaced, right ridges very large with parallel tips oriented downwards. Axis of orientation possibly double.

The scales corresponding to the first and third section are the same (25 µm). This would mean that the female body diameter at the distal part is smaller than at the proximal body, which is at least unusual. The figures, from the text, correspond to two females, enlarging the possibility that they come from different taxa.

3.11.2.2 Bursa

The right lobe is in right latero-dorsal view, the left lobe is in left lateral view, the dorsal lobe is in dorsal view. The pattern is 1-4 in both lobes; right lobe with ray 3 diverging first from common trunk, then rays 4-6 at same level; left lobe with rays 3-4 diverging at same level and ray 6 proximally to these.

3.11.3 Conclusion

The specimens described as Paramelomystrongylus dessetae seem to be a composite of two different taxa, both belonging to the Nippostrongylinae and possessing synlophes with careen. Type I synlophe evokes the male section of the genus Helgenema ( Figs. 10B, 10B’ ) with a weakly developed careen. However, the available data are too limited to conclude that it is the same taxon.

Type II does not resemble any described synlophe and the orientation of the right ridges is unique among the Nippostrongylinae .

Concerning the bursa, we have no elements to attribute the illustrated bursa to a given type of synlophe.

Since we do not know what type of synlophe the holotype corresponds to, Paramelomystrongylus dessetae is considered a species inquirenda. Being the type species of the genus, it is impossible to give a proper definition of this latter. We thus consider Paramelomystrongylus a genus inquirendum.

The two types of synlophe recognized seem to be distributed into two different taxa as follows: “ Paramelomystrongylus dessetae ” (male section at midbody and female sections within proximal and distal body) (with synlophe of Type I); Nippostrongylinae i.s. 6 (female section at midbody) (with synlophe of Type II).

Figures

Figure 8. Genus Missimstrongylus Smales, 2018. A-A” Missimstrongylus oweni Smales, 2018, section at midbody, male. Source: A redrawn from [41]. A’, A” modified figures: A’ rotated 90° clockwise with respect to the original, A” further reversion of A’ on its frontal axis.

Figure 10. Genus Helgenema Smales, 2020. Body sections. A–C’ Helgenema keablei. A, A’ within proximal body, female. B–C’ at midbody. B, B’, male. C, C’ female. D–F’ Helgenema lamia Smales, 2021. D within proximal body, male. E–F’ at midbody. E, E’ male, F, F’, female. Sources: A–C redrawn from [43]. D–F redrawn from [44]. A’–C’, E’, F’ modified sections: A’ reversed on its frontal axis with respect to the original, B’ reversed on frontal axis then rotated ca. 15° clockwise with respect to the original. C’, E’, F’ re-numbering of ridges.

Figure 11. Genus Paramelomystrongylus Smales, 2020. Body sections. A–D’ Paramelomystrongylus dessetae Smales, 2020. A, A’ within proximal body, female. B at midbody, male. C, C’ within distal part, female. D, D’ at midbody, female. A, B, C: Synlophe of type I. D: Synlophe of type II. Source: A–D redrawn from [43]. A’, C’, D’ modified sections: A’, C’ numbering of ridges. D’ rotation clockwise and numbering of ridges with respect to the original.