Geocenamus brevidens ( Allen, 1955 )

Rybarczyk-Mydłowska, Katarzyna, Sikora, Grzegorz & Kubicz, Magdalena, 2022, Morphological and molecular characteristics of Geocenamus longus and the first report of G. brevidens from a karst cave (Nematoda: Merliniidae Siddiqi, 1971), Zootaxa 5134 (3), pp. 383-398 : 390

Identification of Geocenamus brevidens ( Allen, 1955) in the Piekło pod Skibami Cave

After the extraction from the sediment obtained from the Piekło pod Skibami Cave, and subsequent preparation of the permanent slides and microscopic observations, the nematodes were identified as representatives of Geocenamus brevidens ( Allen, 1955) by use of the morphological keys ( Brzeski, 1998 and Geraert, 2011). The morphology and morphometry ( Fig. 3 and Tab. 4 ) of this population were in agreement with the literature as well as with the most recent publications about this species ( Bharti et al., 2020; Munawar et al., 2021; at most to Shokoohi et al., 2022). The herein reported G. brevidens population was for the first time localized in a cave and consisted mostly of females (9 of them were analyzed morphologically and morphometrically) and two male specimens.

Due to a quite difficult origin (cave sediment mixed with plant roots) and the possible presence of some PCR inhibiting substances within the sampled material, of the eight G. brevidens individuals, all genes were sequenced from a single specimen. Multiple 18S and 28S rDNA ( OM618609 and OM618607 ) sequences were obtained from the same DNA whereas mtCOI sequencing failed several times, therefore, only a single mtCOI sequence was obtained in the present study ( OM615894 ). Since various attempts were made to obtain mtCOI sequence, we recommend verification and confirmation of this genetic marker in future studies. Additionally, from each of the other seven nematodes at least one part of the 18S rDNA fragment was acquired. Neither 28S rDNA nor mtCOI additional data was gained from those nematodes. There was no intraspecific variability observed within the independently obtained 18S rDNA sequences except two indels (1 and 2 nucleotide) within one 18S-II sequence ( OM618610 ). The obtained full length 18S rDNA sequence (nearly 1,7 kb) showed the highest percent identity (99,88%; 1 nt difference) with the Merlinius brevidens ( KX789708 ) sequence from Iran. Both sequences were of similar length. The 28S rDNA (1 kb) G. brevidens from this study showed the highest percent identity to the G. brevidens ( MW029449 ) sequence from Canada (100% identity, 71% query coverage), a population which was suggested as the reference population for this species ( Munawar et al., 2021).

Figures

FIGURE 3. Light microscopy images of Geocenamus brevidens, female and male. Female: A) Entire body; B) Pharyngeal region; C) Vulval region; D) Lateral field; E) Tail region; Male: F) Entire body; G) Pharyngeal region; H–I) Tail region with visible spicules and bursa. Scale: 10 µm.