Paramelomystrongylus dessetae, Smales, 2020

Smales, Lesley, 2020, Gastrointestinal nematodes of Paramelomys levipes and P. mollis (Rodentia Muridae) from Papua, Indonesia and Papua New Guinea with the descriptions of three new genera and nine new species (Nematoda), Zootaxa 4861 (4), pp. 544-572 : 563-565

Paramelomystrongylus dessetae n. sp.

( Figs 8 A–K)

Type host. Paramelomys mollis (Thomas)

Site in host. Small intestine.

Type specimens. Holotype male SAMA AHC 49059, allotype female SAMA AHC 49060, paratypes 5 males, 8 females SAMA AHC 49061 from Paramelomys mollis from Kosipe , Papua New Guinea (8° 27´S 147° 13´E); coll. T. Flannery, 1982.

Other material examined. From P. mollis, From Indonesia, Papua, pieces 3 worms, Bichate, Arfak Mountains AM W. 53150.

Etymology. The species name is in recognition of the very significant contribution Dr Marie-Claude Durette- Desset has made to the study of the Trichostrongylina .

Description. General: Tiny, usually straight, nematodes. Cephalic vesicle prominent with about 6 transverse annulations. Buccal capsule vestigial, mouth opening triangular with rudimentary lips; cephalic and labial papillae not seen, 2 lateral amphids. Oesophagus claviform, nerve ring excretory pore and deirids not seen.

Synlophe: (sections of 2 males, 2 females) Longitudinal ridges extend from posterior margin of cephalic vesicle to anterior to bursa or vulva. Dorsal ridges continuous, ventral ridges interrupted; 13–16 ridges, with a type A carene on left lateral side supported by 2 hypertrophied ridges 1, 1’; ridge 1’ larger; 14 ridges in anterior, 14–16 in mid body. Axis of orientation of ridges sub frontal, 6 –7 ridges dorsal side, 9–10 ventral side. Ridges unequal in size; left ridges very large, ridge 1’ larger than ridge 1; dorsal right ridge 6/7 ventral ridge 9´/10´medium sized; other ridges smaller, about same size.

Male: (measurements of 10 specimens) Length 1.3–1.9 (1.6) mm, maximum width 43–60 (48). Cephalic vesicle 20–24 (21) long. Oesophagus 200–300 (257) long; nerve ring, deirids and excretory pore not seen. Bursa dissymmetrical, left lobe slightly larger, pattern of rays 2–3, dorsal lobe shorter than laterals. Dorsal trunk symmetrical divided at about 2/3 its length, dorsal rays 9, 10 symmetrical, rays 8 arising from dorsal trunk at slightly different levels, not reaching margin of bursa; lateral rays 6, 5, 4 all about same size, rays 2, 3 arise together from common trunk, rays 2 short, not reaching margin of bursa. Genital cone not prominent. Spicules equal, filiform, 210–280 (242) long, spicule to body length ratio 15%, Gubernaculum 17–22 (19) long.

Female: (measurements of 12 specimens) Length 1.6–2.0 (1.9) mm, maximum width 40–60 (45). Cephalic vesicle 20–26 (23) long. Oesophagus 250–400 (326) long; nerve ring, deirids, excretory pore not seen. Vulva opens 60–110 (91) from tail tip; tail flexed ventrally. Ovejector monodelphic, infundibulum longest element, 30–40 (35) sphincter shortest element 10–20 (15), vestibule 25–35 (30), vagina 15–20 (18) long. Tail conical with pointed tip, 22–30 (28) long. Eggs thin shelled, ellipsoidal, 4 eggs in utero 59.5–68.0 (63.3) long, 27.2–33.0 (27.2) wide.

Remarks. As noted above these specimens were not in the best condition, their thin fragile cuticle and tiny size made them difficult to handle. Nevertheless, sufficient morphological information could be gathered to characterise the new genus and species. The key of Beveridge et al. (2014) places Paramelomystrongylus n. gen. in the family Heligmonellidae and the subfamily Nippostrongylinae . Using the key of Durette-Desset & Digiani (2015) for the Nippostrongylinae from the Australian region the new genus comes closest to the genus Hasegawanema Durette- Desset & Digiani, 2015 in having 13 –16 ridges with a carene supported by 2 ridges, and the ridges associated with the carene and right lateral side largest ( Durette-Desset & Digiani 2015). Paramelomystrongylus dessetae n. sp. differs from the genus Hasegawanema in having ridges 1, 1´hypertrophied, ridge 1´and right lateral ridges larger than dorsal and ventral ridges. Although P. dessetae has a synlophe with discontinuous ventral ridges and the genus Hasegawanema does not, this character occurs also in the genera Odilia (Mawson, 1961) and Sanduanensis Durette-Desset & Digiani, 2015 and therefore may not be useful for differentiation at the generic level.

The characteristics of those genera that are not restricted to New Guinea or have been described since the key was constructed are listed earlier. Paramelomystrongylus can be distinguished from the genus Mawsonema the only other genus with a Type A carene as follows: Mawsonema has right dorsal ridges larger than right lateral ridges and a sub frontal axis of orientation compared with Paramelomystrongylus which has ridges 1, 1´hypertrophied and right lateral ridges larger than right dorsal ridges ( Smales & Heinrich 2010; Smales 2017).

Figures

FIGURE 8. Paramelomystrongylus dessetae gen. n., sp. n. In all illustrations of the synlophe in transverse section the dorsal aspect of the body is oriented towards the top of the page and the left side of the nematode to the left of the page. The dorsal and ventral (numbers with superscripts) ridges are numbered, as are the lateral rays of the bursa (right rays with superscripts). A. Female, anterior end lateral view showing discontinuous ventral ridges; B. Female, posterior end lateral view showing ovejector; C. Male, mid body transverse section; D. Male, spicules, anterior ends; E. Female, anterior body transverse section; F. Female, mid body transverse section; G. Female, posterior section mid body transverse section; H. Male, spicule lateral view showing gubernaculum and tips; I Male, bursa left lobe; J. Male, bursa dorsal lobe: K. Male, bursa right lobe. Scale bars in µm: a, b, 50; C– K 25.