Rodentanema aenigma, Smales, 2016

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 : 18-20

3.6.1 Analysis of data and difficulties encountered Rodentanema aenigma

3.6.1.1 Head

Illustrations analyzed herein are proximal extremity in lateral (Fig. 27/6A) and apical (28/6B) views. Buccal capsule (Fig. 27/6A) and five lips (Fig. 28/6B), illustrated.

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

Sections analyzed herein are at midbody: male (Figs. 31/6C) and female (32/6D). Lateral cords not illustrated; ridges not numbered.

At midbody: in both sexes, careen absent and ridges subequal, medium-sized. Ridges irregularly spaced, separated by ridge-free spaces (arrowheads).

Figure 6C (male) six ridges separated by three ridge-free spaces (arrowheads): two ridges mid- dorsal oriented from right to left, one ridge right-ventral, three ridges left-ventral; all these latter with unclear orientation.

Figure 6D (female) seven ridges separated by two ridge-free spaces (arrowheads): one ridge mid-dorsal oriented to left, six ventral ridges (three right-ventral, two left-ventral); tips of these two latter groups divergent.

3.6.1.3 Bursa (number of worms studied not specified, illustrated in [ 38]: Figs. 30, 33 and 34)

Figure 30: distal extremity including closed bursa, left lateral view, only rays 3-8 illustrated, rays 4-6 joined up to extremities. Figure 33: bursa “partially unrolled in left lateral and dorsal aspects”, only dorsal ray and left rays 4-8 illustrated, extremities of left rays 4-6 diverging. Figure 34: dorsal lobe, orientation not specified. Right lobe not illustrated. From generic definition [ 38], bursa dissymmetrical with right lobe larger; whereas from description, left lobe larger. From generic definition, pattern of type 1-4.

3.6.2 Comments

3.6.2.1 Head

In the original written description, the cephalic vesicle is indicated as present but is not illustrated. On the other hand, lips and teeth are indicated as absent, but the illustration in apical view shows clearly five lips (Fig. 28 in [ 38]), which is undoubtedly a drawing flaw since these structures appear in number of six.

3.6.2.2 Synlophe

The position of the ridges and the inclination of the axis are very different between both sexes.

In Figure 6C (male), the tip of the only ridge situated on right-ventral quadrant is perpendicular to the body surface but clearly divergent from the tips of the dorsal ridges. The remaining ventral ridges are also oriented perpendicularly to body surface, there are no convergent tips and the inclination of the axis of orientation remains uncertain.

Figure 6D (female); if the section is reversed on its sagittal axis, then turned about 75° counterclockwise we obtain a section whose synlophe is similar to that of other Heligmosomoidea in which the axis is subfrontal ( Fig. 6D’ ).

Based on these observations, two types of synlophe could be described: Type I ( Fig. 6C ) characterized by 6 ridges at midbody grouped into three sets with inclination of axis of orientation uncertain. Type II ( Fig. 6D’ ) characterized by 7 ridges at midbody grouped into two sets with inclination of axis of orientation perhaps subfrontal.

The presence of a cephalic vesicle, a developed buccal capsule, and six lips indicate that the specimens studied do not belong to the Heligmonellidae but should rather be assimilated with the Herpetostrongylidae : Herpetostrongylinae (parasitic in reptiles, Australian marsupials and exceptionally in rodents). The Herpetostrongylinae possess the same cephalic characters described above, plus 1-3 oesophageal teeth (not observed by the author in Rodentanema ). Besides the cephalic characters, the Herpetostrongylinae possess a synlophe with an axis of orientation oblique or subfrontal, bursae of different types including the type 1-4, females didelphic or monodelphic, and female tails with or without a spine.

Among the Herpetostrongylinae, only two genera are characterized by females which are monodelphic and without a caudal spine: Dessetostrongylus Humphery-Smith, 1981 , parasitic in Dasyuridae (Marsupialia) in Australia, and Papuastrongylus Smales, 2010 parasitic in Muridae from Papua New Guinea. The two genera are differentiated from the specimens described as Rodentanema by having well-developed buccal capsules and a different synlophe pattern.

3.6.2.3 Bursa

According to [ 38], Figures 30 and 33 illustrate the left lobe. But both figures are clearly different, particularly concerning left ray 8, which in Figure 33 is seen mostly parallel to ray 6 and in Figure 30 it diverges proximally from it. Figures 30 and 33 correspond clearly to different bursae, which may imply the presence of two different species among the type material. In addition, the right lobe is not illustrated, the description of the bursa is very brief and ambiguous and in the absence of an illustration of ray 2, the pattern cannot be determined.

3.6.3 Conclusion

There seem to be two taxa concerned in the description of this species (each characterized by a different synlophe): “ R. aenigma ” and a Herpetostrongylidae i.s. The uncertain orientation of the ridges, the incomplete description of the bursa, plus the fact that we do not know what type of synlophe the holotype corresponds to, Rodentanema aenigma is considered a species inquirenda. Being the type and unique species of the genus, it is impossible to give a precise definition of it. We thus consider Rodentanema a genus inquirendum.

Figures

Figure 6. Genus Rodentanema Smales, 2016. A–D’. Rodentanema aenigma Smales, 2016. A–B’ head. A lateral or median view showing buccal capsule. B, B’ apical view. C, D sections at midbody. C male, D, D’ female. Abbreviations: bc buccal capsule. Source: A–D redrawn from [38]. B’, D’ modified figures: B’ six lips instead five. D’ rotated 90° counterclockwise with respect to the original.