Helgenema keablei, 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 : 553-555

Helgenema keablei n. sp.

( Figs 3 A– K)

Type host. Paramelomys levipes (Thomas)

Site in host. Small intestine.

Type specimens. Holotype male AM W. 53156, allotype female AM W. 53157, paratypes 2 males, 2 females AM W. 53148, from Paramelomys levipes from Munimum Village , Milne Bay Province, Papua New Guinea (9° 53´S 149° 23´E); coll. P. German, 7. viii. 1992.

Etymology. The species name is in recognition of the work of Stephen Keable, curator of the helminth collection at the Australian Museum, Sydney.

Description. General: Small slender worms, may be coiled. Cephalic vesicle prominent with about 4 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 pointed ridges extend from posterior margin of cephalic vesicle to anterior to bursa or vulva; with 13–14 ridges in males, 11–15 in females; 13 ridges in males, 9–11 in females in anterior body; 14 ridges in males, 15 in females in mid body; 15 ridges in females in posterior body. Cuticular dilatation of left side, supported anteriorly by large ridge 1’ becoming smaller posteriorly; other ridges small without size gradient at mid body. Axis of orientation of ridges sub frontal; 7–8 ridges dorsal side, 7–8 ventral side males and females.

Male: (measurements of 5 worms) Length 2.5 – 3.4 (2.7) mm, maximum width 30–66 (46). Cephalic vesicle 17–20 (19) long. Oesophagus 270, 310 (2 measurements) long; nerve ring, deirids and excretory pore not seen. Bursa relatively small, dissymmetrical, left lobe larger; pattern of rays 2–3. Dorsal lobe shorter than laterals; dorsal trunk symmetrical divided at about ½ its length, terminal divisions rays 9, 10, not reaching margin of bursa; lateral rays 6, 5, 4 about same size, reaching margin of bursa, rays 3, 2 arise together from common trunk, reaching margin of bursa. Genital cone simple. Spicules equal, filiform, tips curved, 170–210 (190) long; spicule to body length ratio 7.2 %. Gubernaculum 18, 19 (2 measurements) long.

Female: (measurements of 5 specimens) Length 2.4 –3.0 (3.6) mm, maximum width 47–60 (55). Cephalic vesicle 23–26 (25) long. Oesophagus 210–380 (294) long; nerve ring, deirids, excretory pore not seen. Vulva opens 90–110 (103) from tail tip, posterior end reflexed ventrally. Ovejector monodelphic, infundibulum longest element, 80 long, sphincter 30, vestibule 50, vagina 25 long. Tail conical with pointed tip, 40–50 (45) long. Eggs thin shelled, ellipsoidal, 2–4 in utero, 63 long, 33 wide.

Remarks. Using the key of Beveridge et al. (2014) the new genus can be placed in the family Heligmonellidae and the subfamily Nippostrongylinae . From the key to the genera of Australasian Nippostrongylinae of Durette- Desset & Digiani (2015) Helgenema n. gen. differs from all other genera in having a synlophe with a left cuticular dilatation supported anteriorly by a left lateral ridge 1’. Helgenema keablei n. sp., with a synlophe of 13 – 15 ridges with a sub frontal orientation and a left cuticular dilatation can be distinguished further from the 20 genera that have been reported in or described from the Sahul and Malaysian regions and were not included in the key of Durette-Desset & Digiani (2015) as follows: Flannerystrongylus, Smales, 2019 , Montistrongylus Smales & Heinrich, 2010 , Sabanema Ow-Yang, Durette-Desset & Obayashi, 1983 and Parasabanema Smales & Heinrich, 2010 lack a left cuticular dilatation of the syniophe. The cosmopolitan genus Nippostrongylus, Lane, 1923 has a synlophe with a carene supported by a single hypertrophied ridge; Hasegawanema Durette-Desset & Digiani, 2015 and Odilia Durette- Desset, 1973 have synlophes with type A carenes (see Smales & Heinrich 2010); Heligmonoides Baylis, 1928 and Maxomystrongylus Hasegawa & Syafruddin, 1997 have type B carenes (see Smales & Heinrich 2010); Orientostrongylus Durette-Desset, 1970 has a primitive arrangement of the synlophe. Hasanuddinia Hasegawa & Syafruddin, 1994 has a synlohe with left ventral and right dorsal ridges largest; Malaistrongylus Ow-Yang , Durette- Desset & Obayashi, 1983 has left and right dilatations of the synlophe; Rattustrongylus Ow-Yang, Durette-Desset & Obayashi, 1983 has 18–19 synlophe ridges with the left dorsal ridges smallest. Bunomystrongylus Hasegawa & Mangali, 1996 has rounded as well as pointed longitudinal ridges; Melomystrongylus Smales & Heinrich, 2010 , has the anterior portion of the ventral ridge hypertrophied; Mawsonema Smales & Heinrich, 2010 has a type A carene with sub frontal ridges and ridge 1 larger than ridge 1´; Krishnasamyos Digiani & Durette-Desset, 2014 has 19–20 ridges, ridge 1´forming a comarete and the right ridge minute; Syafruddinema Digiani & Durette-Desset, 2014 has small to minute unevenly sized ridges; Nugininema Smales 2016 has 17 ridges mid body, the ventral and ventral right ridges hypertrophied; Parvinema Smales, 2017 has a synlophe with a carene supported by the hypertrophied ridges 1, 1´and ventral right ridges larger than dorsal right ridges; Missimstrongylus Smales, 2018 has a synlophe with the ventral ridge 5´the largest ( Lane 1923; Baylis 1928; Durette-Desset 1970; Ow-Yang et al. 1983; Hasegawa & Syafruddin 1994, 1997; Hasegawa & Mangali 1996; Smales & Heinrich 2010; Digiani & Durette-Desset 2014; Durette-Desset & Digiani, 2015; Smales 2016, 2017, 2018a, 2019).

Figures

FIGURE 3. Helgenema keablei 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. Male, transverse section mid body; B. Female, anterior body transverse section; C. Female, anterior end lateral view; D. Spicules, anterior ends; E. Female, mid body transverse section; F. Male, gubernaculum and spicule tip, lateral view. G. Female, posterior body transverse section; H. Female, posterior end lateral view; I. Male, bursa left lobe; J. Male, bursa dorsal lobe; K. Male, bursa right lobe. Scale bars in µm: A, B, E, G, I, J, K, 25; H, 50; D, F, 12.5.