Geocenamus brevidens ( Allen, 1955 ) Siddiqi, 1970

Munawar, Maria, Yevtushenko, Dmytro P. & Castillo, Pablo, 2021, Integrative taxonomy, distribution, and host associations of Geocenamus brevidens and Quinisulcius capitatus from southern Alberta, Canada, Journal of Nematology 53 (1), pp. 1-17 : 3

Geocenamus brevidens ( Allen, 1955) Siddiqi, 1970 ( Fig. 1 and Table 1 ).

Description

Female

Body straight with curved tail region or open C-shaped. The cuticle annulated, lateral field with six incisures. Cephalic region continuous, broadly rounded with 3 to 4 indistinct annuli, basal ring of head framework shallow, distinctively arched. Stylet 15 to 17 µm long with rounded basal knobs. Dorsal gland opening (DGO) 1.5 to 3.0 µm posterior to basal knobs. Median bulb spherical to oval, well-developed, central valve plates bean-shaped slightly anteriorly. Isthmus slender encircled with nerve ring. Deirids were present (observed in few specimens). Excretory pore anterior to the basal esophageal bulb. Hemizonid 2 to 3 body annuli long situated slightly anterior to the excretory pore. Cardia rounded, intestine densely globular. Ovaries outstretched, vulva with small epiptygma, which mostly appear as protruding lips, vagina inclined anteriorly covering half of the corresponding body diameter. Spermatheca rounded, scarcely filled with sperm. Tail subcylindrical, gradually tapering to a smooth broadly rounded or truncated terminus. Hyaline region of tail prominent 3.2–5.5µm long. Phasmids near or slightly posterior to mid-tail.

Male

Not found.

Remarks

Geocenamus brevidens (= Tylenchorhynchus brevidens, Allen, 1955 and Merlinius brevidens, Siddiqi, 1970 ) was originally described in the rhizosphere of grass from the USA by Allen in 1955. Since then, this species has been reported from diverse climate regions and agricultural environments ( Table 3 ). Despite its wide distribution, few morphometrical studies are available for comparison ( Table 1 ). Geocenamus brevidens was also reported from potato fields in Ontario ( Olthof et al., 1982), although no morphological and morphometric studies were presented. Hence, we consider our population of G. brevidens as a Canadian population. We observed that nematodes of the Canadian population of G. brevidens were slightly longer and wider than in the original and other reported descriptions, with the exception of those from India ( Siddiqi, 1961). The Canadian population morphometrical values were in good agreement with the Indian population, except for the stylet length, which was longer in the Canadian population, 15.0 to 17.5 vs 13.0 to 15.0µm. The other morphological characteristics, i.e., lip and tail morphology, overall body habitus, and vulva appearance, were consistent with the original description. Males were described in the original description and by Siddiqi (1961), but in later reports, no males were ever detected. Geraert (2011) mentioned that males were uncommon in G. brevidens ; the Canadian population was also found devoid of males. In the original and subsequent descriptions, the authors did not observe the presence of spermatheca in G. brevidens ( Allen, 1955; Alvani et al., 2017; Tzortzakakis et al., 2018). On the other hand, round-shaped spermathecae were found in the Canadian and Indian populations. The other characteristics noted by Siddiqi (1961) in the Indian population were tightly closed stylet knobs, indistinct anus, and rather cylindrical tail. In the Canadian population, the anus was prominent, stylet knobs were rounded, and the tail was cylindrical with a broadly rounded, somewhat truncated terminus. We consider these small differences between G. brevidens populations to be due to intraspecific geographic variation.

Figures

Figure 1: Light photomicrographs of GeOCenamUS BrevidenS. (A) Entire female, (B) Esophageal region, (C) Lip region, (D) Posterior esophageal region, (E) Deirids, (F) Posterior region with complete reproductive system, (G) Lateral lines, (H-J) Vulval region, (K-O) Female tails. Scale bars: (A) 50μm; (B-D, E, H-O) 20μm, (F) 50μm, (G) 5μm. Arrows point to (a) anus, (d) deirids, (exp) excretory pore, (ph) phamsid, and (v) vulva.