Pogonomystrongylus, Smales, 2014

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 : 15-17

3.4 Genus POGONOMYSTRONGYLUS Smales, 2014 ( Fig. 4 )

Type and sole species: Pogonomystrongylus domaensis Smales, 2014 .

Hosts: Muridae , Murinae ( Rodentia ).

Host site: small intestine.

Distribution: Papua New Guinea.

Original diagnosis: Nippostrongylinae . Synlophe well developed with 7-10 continuous pointed longitudinal ridges, single left ventral ridge hypertrophied: axis of orientation of ridges sub frontal. Bursa asymmetrical, right lobe larger. Pattern of bursal rays 2-3, dorsal ray divided distal to branching of rays from dorsal trunk. Parasites of hydromyine murids [ 36].

3.4.1 Analysis of data and difficulties encountered

3.4.1.1 Synlophe (number of worms studied not provided)

Sections analyzed herein are those within proximal body: male (Fig. 37/4A) and female (Fig. 38/4B), and at midbody:

male (Fig. 40/4C) and female (Fig. 41/4D). Lateral cords illustrated and ridges numbered only in Figure 40/4C.

In all sections, careen absent and ridges grouped into three sets alternating with three ridge-free spaces, indicated by arrowheads. Ridge sets are numbered herein (as set 1, set 2, set 3) starting from left and clockwise. In all sections, position of the sets and ridge-free spaces the same: ridge set 1 situated on left side and made up of sole large ridge whose tip directed to ventral side ( Figs. 4A, 4B, 4C ) or perpendicular to body surface ( Fig. 4D ). Ridge set 3 made up of four small ridges regularly spaced and subequal, oriented from right to left. In all sections, axis of orientation described as subfrontal in [ 36].

Within proximal body: in Figure 4A (male), ridge set 2 made up of three medium-sized ridges regularly spaced oriented from right to left. Figure 4B (female), ridge set 2 made up of four ridges (two small, two medium-sized) oriented from right to left.

At midbody: in Figure 4C (male), ridge set 2 made up of five small ridges, ridges 4 to 1 showing decreasing size gradient and oriented from right to left plus minute ridge 5 perpendicular to body.

Figure 4D (female), ridge set 2 made up of six small to minute ridges oriented from right to left with decreasing size gradient from right to left.

3.4.1.2 Bursa (number of worms studied not provided,

illustrated in [ 36]: Figs. 42, 44 and 45)

Figure 42: dorsal ray and rays 8, orientation not specified. Figure 44: left lateral lobe and Figure 45: right lateral lobe. Genital cone developed (though “not prominent” from the written description). From the generic definition, bursa

dissymmetrical with right lobe slightly larger and pattern of type 2-3.

3.4.2 Comments

3.4.2.1 Synlophe

In sections 4A and 4B, the ridges determine, in spite of the interpretation of Smales [ 36], an oblique axis of orientation directed from the right-dorsal to the left-ventral quadrant, and this is mainly due to the fact that the tip of ridge 1’ is directed to the ventral side. By definition, the axis of orientation of the Heligmosomoidea is directed from the right-ventral to the left-dorsal quadrant; in addition, in the Heligmonellidae , the tip of ridge 1’ is always directed to the dorsal side. If the sections are reversed on their frontal axis, then slightly rotated clockwise ( Figs. 4A’ , 4B’), the inclination of the axis of orientation becomes oblique (and not subfrontal), directed from the right-ventral to the left-dorsal quadrant.

In section 4C, the axis is not subfrontal since it does not pass through the lateral cords. If the section is reversed on its frontal axis, then slightly rotated clockwise, the tip of ridge 1’ is directed dorsally and the axis becomes oblique ( Fig. 4C’ ).

In section 4D, it is sufficient to turn the section clockwise 45° to obtain a new interpretation ( Fig. 4D’ ) which is congruent with the re-oriented sections 4A’–4C’.

3.4.2.2 Bursa

Captions and drawings contradict each other. In Figure 44, the genital cone is illustrated above the rays, which means that the lobe is seen in ventral view, and it is actually the right lobe.

M.-C. Durette-Desset and M.C. Digiani: Parasite 2023, 30, 63 17 In Figure 45, the dorsal lobe is clearly visible and at the right side of the figure is folded ventrally which means that the bursa is seen in dorsal view and the illustrated lobe is actually the left lobe. Figure 42 is clearly in dorsal view. The genital cone is clearly prominent since its length attains 50% of the bursal length. Judging from the illustrations, the pattern is 1-4 in both lobes. In right lobe, ray 2 very short, ray 3 diverging first from common trunk to rays 3-6, then ray 6. In left lobe, rays 2 and 3 very long, rays 3 and 6 diverging at same level from their common trunk.

3.4.3 Conclusion

If our interpretation of the synlophe and bursa are accurate, we consider Pogonomystrongylus a valid genus. However, due to the ambiguous descriptions of both the synlophe and bursa, further studies either on the type material or on new material would be necessary to provide a new definition of the genus. Pogonomystrongylus shares with Melomystrongylus , Hasanuddinia and Montistrongylus Smales, 2010 the following features: (1) careen absent and (2) alternation of ridge sets with ridge-free spaces. Pogonomystrongylus is distinguished from the three mentioned genera by the absence of ventral comaretes and by the presence of a large left ridge.

3.4.4 Emended diagnosis

Pogonomystrongylus . Synlophe without careen. Ten ridges in male, 11 in female. Ridges irregularly spaced, grouped into three sets alternating with three ridge-free spaces. Ridge 1’ largest, flanked on both sides by ridge-free spaces. Other ridges small to medium-sized. Slight decreasing gradient in ridge size from right to left on both dorsal and ventral sides. Axis of orientation oblique. Bursal characteristic pattern of type 1-4 in both lobes.

Figures

Figure 4. Genus Pogonomystrongylus Smales, 2014. Body sections. A–D’ Pogonomystrongylus domaensis Smales, 2014. A–B’ within proximal body. A, A’ male, B, B’ female. C–D’ at midbody. C, C’ male, D, D’ female. Source: A–D redrawn from [36]. A’–D’, modified figures: A’–C’ reversed on their frontal axes with respect to the originals, then slightly rotated clockwise. D’ rotated 45° clockwise.