Introduction
Nesterov (Reference Nesterov1970) proposed the genus Acromoldavicus Nesterov, Reference Nesterov1970 to accommodate the species previously described as Acrobeloides skrjabini by Nesterov and Lisetskaya (Reference Nesterov and Lisetskaya1965). Also, this author placed this genus in the subfamily Acrobelinae Thorne, Reference Thorne1937 within the family Cephalobidae Filipjev, Reference Filipjev1934. Thereafter, Andrássy (Reference Andrássy1976) proposed the new subfamily Kirjanoviinae Andrássy, Reference Andrássy1976 within the family Cephalobidae and transferred the genus Acromoldavicus to this new subfamily. Later, Karegar et al. (Reference Karegar, De Ley and Geraert1997) reported several morphological similarities between Acromoldavicus and Elaphonema Heyns, Reference Heyns1962 and therefore transferred the subfamily Kirjanoviinae to the family Elaphonematidae, which was previously suggested by Nesterov (Reference Nesterov1979).
Currently, the genus Acromoldavicus contains two valid species: A. mojavicus Baldwin, De Ley, Mundo-Ocampo, De Ley, Nadler and Gebre, Reference Baldwin, De Ley, Mundo-Ocampo, De Ley, Nadler and Gebre2001, which was only described in sandy soil from the Mohave Desert by Baldwin et al. (Reference Baldwin, De Ley, Mundo-Ocampo, De Ley, Nadler and Gebre2001), and A. skrjabini (Nesterov and Lisetskaya, Reference Nesterov and Lisetskaya1965) Nesterov, Reference Nesterov1970, which has been found in agricultural soils from several countries: Nesterov and Lisetskaya (Reference Nesterov and Lisetskaya1965) and Nesterov (Reference Nesterov1970, Reference Nesterov1979) in Moldavia, Boström (Reference Boström1989, Reference Boström1992) in Greece, Karegar et al. (Reference Karegar, De Ley and Geraert1997) in Iran and Spain, Susulovsky et al. (Reference Susulovsky, Boström and Holovachov2001) in Ukraine and Israel, Iliev et al. (Reference Iliev, Ilieva and Mitor2003) in Bulgaria, and recently in Spain, Abolafia et al. (Reference Abolafia, Hosseinvand and Eskandari2021). The genus Acromoldavicus Nesterov, Reference Nesterov1970 is an infrequent taxon belonging to the infraorder Cephalobomorpha De Ley and Blaxter, Reference De Ley, Blaxter and Lee2002, superfamily Cephaloboidea Filipjev, Reference Filipjev1934, family Elaphonematidae Heyns, Reference Heyns1962.
Acromoldavicus is characterized by having cuticle tessellated, lip region with modified lips, flattened labial probolae, primary axils broad with triangular guard processes, secondary axils narrow lacking guard processes, stoma short and tubular with reduced rhabdia, pharynx with basal bulb bearing well developed and striated transverse valves, female system monodelphic-prodelphic with vulva not prominent and rectum very long, and males infrequent.
In this study, a new species of the genus Acromoldavicus is described from two localities of the southeast Iberian Peninsula found in sand dunes and sandy soil using morphological, morphometric, and molecular characterization. Additionally, a key for the species identification of the genus Acromoldavicus is provided.
Material and methods
Nematode extraction and processing
Soil samples were collected from natural areas (Figure 1) and processed following several nematological techniques, which were described in detail by Abolafia (Reference Abolafia2022). The nematodes were extracted from sandy soil using the modified Baermann’s (Reference Baermann1917) funnel technique, killed by heat, and fixed in a 4% formaldehyde solution (except for specimens used for molecular analyses, which were not fixed). The nematodes were processed to anhydrous glycerine according to Siddiqi’s (Reference Siddiqi1964) method, using lactophenol-glycerine solutions, and were permanently mounted on glass microscope slides with the glycerine-paraffin method (de Maeseneer and d’Herde Reference de Maeseneer and d’Herde1963) somewhat modified using hot liquid paraffin.
Figure 1. Map of Spain showing landscape views of the study area: (a) Tabernas Desert and (b) Salinas de Cabo de Gata; and xerophilic vegetation associated with A. xerophilus n. sp.: (c) Nicotiana glauca Graham; (d) Limonium insigne (Coss.) Kuntze; (e) Carduus tenuiflorus Curtis; (f) Arthrocnemum macrostachyum (Moric.) C. Koch.; (g) Launaea arborescens (Batt.) Murb; (h) Ephedra fragilis Desf; (i) Helianthemum almeriense Pau; (j) Caroxylon vermiculatum (L.) Akhani and Roalson; (k) Limbarda crithmoides (L.) Dumort; (l): Salsola kali L.; (m) Onthatus maritimus Hoffmanns and Link; (n) Thymelaea hirsuta (L.) Endl.
Light microscopy (LM)
Photomicrographs were taken with a Nikon Eclipse 80i (Nikon, Tokyo, Japan) microscope provided with differential interference contrast (DIC) optics and a Euromex sCEMX-6 camera (Euromex Microscopen BV, Arnhem, The Netherlands). The micrographs were edited using Adobe® Photoshop® CS (Adobe Inc., San José, California, USA), and figures were mounted using Microsoft® PowerPoint® (Microsoft Corporation, Redmond, Washington, USA). Demanian indices (de Man Reference de Man1881) and other ratios were calculated. The terminology used for the morphology of stoma and spicules/gubernaculum follows the proposals by De Ley et al. (Reference De Ley, van de Velde, Mounport, Baujard and Coomans1995) and Abolafia and Peña-Santiago (Reference Abolafia and Peña-Santiago2017), respectively.
Scanning electron microscopy (SEM)
Specimens preserved in glycerin were selected for observation under SEM according to Abolafia (Reference Abolafia2015). The nematodes were hydrated in distilled water, dehydrated in a graded ethanol-acetone series, critical point dried, coated with gold, and observed with a Zeiss Merlin microscope (5 kV) (Zeiss, Oberkochen, Germany).
DNA extraction, PCR, and sequencing
Specimens were processed according the Abolafia and Ruiz-Cuenca (Reference Abolafia and Ruiz-Cuenca2021) methodology. Nematode DNA was extracted from single fresh specimens using the proteinase K protocol and PCR assays as described Castillo et al. (Reference Castillo, Vovlas, Subbotin and Troccoli2003), albeit somewhat modified (Archidona-Yuste et al. Reference Archidona-Yuste, Navas-Cortés, Cantalapiedra-Navarrete, Palomares-Rius and Castillo2016). The specimens were cut into small pieces using a sterilized dental needle on a clean slide with 18 ml of TE (Tris-EDTA) buffer [10 mM Tris-Cl (tris hydrochloride) + 0.5 mM EDTA (ethylene-diamine-tetra acetic acid); pH=9.0], transferred to a microtube, adding 2 μl proteinase K (700 μg/ml) (Roche, Basel, Switzerland), and stored to -80ºC within 15 min (for several days). The microtubes were incubated at 65°C (1 h), then at 95°C (15 min). For DNA amplification, 3 μl of the extracted DNA was transferred to a microtube containing: 0.6 μl of each primer (10 mM), 3 μl Master Mix Taq DNA Polymerase (5x Hot FirePol Blend Master Mix, Solis BioDyne, Tartu, Estonia), and double distilled water (ddH2O) to a final volume of 20 μl. The primers used for amplification of the region of 18S rRNA gene were the forward primer 988F (5′-CTCAAAGATTAAGCCATGC-3′) and the reverse primer 1912R (5′-TTTACGGTCAGAACTAGGG-3′) (Holterman et al. Reference Holterman, van der Wurff, van den Elsen, van Megen, Bongers, Holovachov, Bakker and Helder2006). The primers used for amplification of the D2-D3 region of 28S rRNA gene were the D2A (5’-ACAAGTACCGTGAGGGAAAGTTG-3’) and the D3B (5’-TCGGAAGGAACCAGCTACTA-3’) primers (Nunn Reference Nunn1992; De Ley et al. Reference De Ley, Felix, Frisse, Nadler, Sternberg and Thomas1999). PCR cycle conditions were as follows: one cycle of 94°C for 15 min., followed by 35 cycles of 94°C for 45 s + annealing temperature of 55°C for 45 s + 72°C for 45 s, and finally one cycle of 72°C for 5 min. After DNA amplification, 5μl of product was loaded on a 1% agarose gel in 0.5% Tris-acetate-EDTA (40 mM Tris, 20 mM glacial acetic acid and 2 mM EDTA; pH=8) to verify the amplification using an electrophoresis system (Labnet Gel XL Ultra V-2, Progen Scientific, London, UK). The bands with DNA products were stained with SYBR Green I (10,000x concentrate in DMSO; Invitrogen, Waltham, USA) and the DNA-loading buffer 6x (GeneON, Ludwigshafen, Germany). The sequencing reactions of the PCR products were performed at Sistemas Genómicos (Paterna, Valencia, Spain) according to the Sanger et al. (Reference Sanger, Nicklen and Coulson1977) method. The sequences obtained were submitted to the GenBank database. The obtained sequences were deposited in NCBI GenBank under accession numbers PP069740 and PP069741 (18S rDNA) and PP069742 (28S rDNA).
Phylogenetic analyses
For phylogenetic relationships, analyses were based on 18S and 28S ribosomal DNA (rDNA) fragments. The newly obtained sequences were manually edited using Chromas 2.6.6 (Technelysium, Queensland, Australia) and aligned with another 18S or 28S rDNA sequences available in GenBank using the ClustalW (Thompson et al. Reference Thompson, Higgins and Gibson1994) alignment tool implemented in MEGA7 (Kumar et al. Reference Kumar, Stecher and Tamura2016). Poorly aligned regions at extremes were removed from the alignments using MEGA7. The best-fit model of nucleotide substitution used for the phylogenetic analysis was statistically selected using jModelTest 2.1.10 (Darriba et al. Reference Darriba, Taboada, Doallo and Posada2012). Phylogenetic trees were generated with the Bayesian inference method using MrBayes 3.2.6 (Ronquist et al. Reference Ronquist, Teslenko, van der Mark, Ayres, Darling, Höhna, Larget, Liu, Suchard and Huelsenbeck2012). Aphelenchus avenae (JQ348399) for 18S rDNA and Teratolobus sp. (KJ652552) for 28S rDNA were chosen as outgroups. The analysis under a General Time Reversible Plus Invariant sites plus Gamma distribution (GTR+I+G) model was selected with a random starting tree and run with the Markov Chain Monte Carlo (MCMC) method (Larget and Simon Reference Larget and Simon1999) for 1 x 106 generations. The resulting trees were visualised and saved with FigTree 1.4.4 (Rambaut Reference Rambaut2018).
Results
Acromoldavicus xerophilus n. sp
Zoobank: urn:lsid:zoobank.org:act:93E003AF-1F8F-42FF-AD42-A5F0F9432294
Material examined
Twenty-one females (holotype and paratypes) from Salinas de Cabo de Gata and fifteen females from Tabernas Desert (province of Almería, Spain) were examined.
Description
Figure 2. Acromoldavicus xerophilus n. sp. (female). (a) neck; (b) lip region in ventral view; (c) reproductive system; (d) entire body; (e) tail; (f) lateral field.
Figure 3. Acromoldavicus xerophilus n. sp. (light microscopy, female). (a) lip region; (b) reproductive system; (c) lateral field at deirid level (arrow); (d) uterine egg; (e) spermatheca with spheroid structure containing small round corpuscles (arrow); (f) entire body (black arrow pointing to the vulva, white arrow pointing to the anus); (g) lateral field.
Figure 4. Acromoldavicus xerophilus n. sp. (light microscopy, female). (a–c) neck region showing the morphological variation of the isthmus and position of the excretory pore (black arrow pointing to the excretory pore, white arrow pointing to the deirid); (d–h) posterior region showing the morphological variation of the tail (arrow pointing to the cellular-cuticular limit at the rectum, black arrow pointing to the phasmid).
Figure 5. Acromoldavicus xerophilus n. sp. (scanning electron microscopy, female). (a, c) lip region in ventral view; (b) oral opening; (d–g) lip region in frontal, subdorsal, dorsal, and left lateral views, respectively. Black arrows pointing to the lateral axillar guard process; white arrows pointing to the amphids.
Figure 6. Acromoldavicus xerophilus n. sp. (scanning electron microscopy, female). (a, b) Neck region in ventral and left lateral views, respectively (white arrow pointing to the excretory pore, black arrow pointing to the deirid); (c) excretory pore in ventral view (arrow); (d) excretory pore in lateral view (black arrow) and deirid (white arrow); (e) lateral field; (f) vulva in ventral view; (g) entire body; (h, i) tail in left lateral and ventral views, respectively (arrow pointing to the left phasmid).
Table 1. Morphometrics of Acromoldavicus xerophilus n. sp. from Spain. Measurements in μm and in the form: mean ± standard deviation (range) where appropriate
Demanian indices (de Man Reference de Man1881): a = body length/body diameter; b = body length/pharynx length; c = body length/tail length; c’ = tail length/anal body diameter; V = (distance from anterior region to vulva/body length) x 100.
Female. Body stout, 0.55–0.70 mm long. Habitus sigmoid, C-shaped o slightly curved ventrally after fixation. Cuticle tessellated, 1–2 μm thickness, having transversal incisures forming annuli with 2–3 μm of thickness at mid-body and longitudinal incisures dividing the cuticle in small and rectangular blocks. Lateral field 6–7 μm wide, occupying 17–24% of mid-body diameter, with two alae limited by three longitudinal incisures, beginning at the anterior third of the neck and continuing to near tail terminus. Lip region continuous with body contour having three pairs of expanded lips, one dorsal and two subventral. Lips bearing an acute process at tip bent to the oral opening and a large expansion outwards or vexillum (pl. vexilla), acute at anterior side and with a filiform process at posterior side. Primary axils V-shaped, having a triangular guard process, larger at ventral primary axil and smaller and fused to the adjacent lateral lip at subdorsal primary axils. Secondary axils U-shaped, all of them lacking guard processes. Amphids oval, located almost apical at each lateral lip. Sensilla papilliform, appearing both labial and cephalic papillae almost apical at each lip, except the lateral ones lacking the cephalic papilla. Oral opening almost triangular, surrounded by three pentagonal labial probolae, connected at their base to each other. Stoma short and tubular: cheilostom short with small and rounded to elongated rhabdia; gymnostom reduced with very small rhabdia; stegostom robust, muscular, with prostegostom having rhabdia directed toward the stoma lumen, meso-, meta- and telostegostom with small rhabdia, scarcely visible. Pharynx cephaloboid: pharyngeal corpus subcylindrical, 2.2–3.9 times isthmus length; isthmus more slender, slightly narrower than metacorpus; basal bulb pyriform, bearing well-developed and striated transverse valves. Cardia more or less conoid. Nerve ring at 61–76% of neck length, surrounding isthmus. Excretory pore at 63–85% of neck length, at isthmus level. Deirids at 83–96% of neck length, at level of basal bulb or at posterior part of isthmus. Reproductive system cephaloboid, monodelphic-prodelphic, in dextral position to intestine: ovary long posteriorly directed, with or without flexures posterior to vulva; ovary differentiated at its junction with the junction in a diverticulum having ovoid small cells at its lumen; oviduct short; spermatheca well developed, 0.7–1.6 times body diameter, divided in two sections, a proximal tubular part with narrow lumen and a distal part swollen with a spheroid structure containing very small rounded corpuscles; uterus tubular, 1.6–3.1 times body diameter long, differentiated in a long distal tubular part with a scarce lumen and thick walls, and a short proximal swollen part with thinner walls and distinct lumen; post-vulval uterine sac reduced, 0.6–0.9 times the corresponding body diameter long, with two sections, the proximal one similar to the swollen part of the uterus, and the distal one more swollen lacking lumen; vagina slightly sigmoid, 34–45% of body width; uterine eggs elongate, about three times longer than wide; vulva a ventral slit, not prominent. Rectum very long, 1.7–2.2 times anal body diameter; three small gland-like cells are distinguishable around the intestine-rectum junction. Tail conoid, slightly curved ventrally, with terminus scarcely biacute, being the dorsal tip smaller. Phasmids located at 33–50% of tail length.
Male. Unknown.
Etymology
The specific name refers to the presence of this species in xeric or water-lacking environments [from ancient greek ξηρός (xērós, “dry”) and φίλος (philos, “love/friendship”)].
Diagnosis
Acromoldavicus xerophilus n. sp. is characterised by its body length (557–700 μm in females), cuticle tessellated, lateral fields with three longitudinal incisures, lips with a large labial expansion, primary axils with a triangular guard process with the ventral one larger, secondary axils lacking guard processes, amphids oval, labial probolae pentagonal, stoma short with prostegostom bearing prominent rhabdia directed towards the stoma lumen, pharynx cephaloboid, nerve ring surrounding the isthmus, excretory pore at isthmus level, female reproductive system monodelphic-prodelphic, spermatheca 0.7–1.6 times the corresponding body diameter, post-vulval sac reduced 0.6–0.9 times body diameter long, rectum 1.7–2.2 times anal body diameter, female tail conoid (30–38 μm long, c=15.8–22.4, c’=1.5–2.0) with biacute terminus and males unknown.
Relationships
Acromoldavicus xerophilus n. sp. is similar to other species of the genus, especially A. mojavicus, by having a lip region with very expanded lips. However, the new species differs in having cuticle with quadrangular block (vs. rectangular in general), lips with larger lobular expansion (7–9 vs. 6–8 μm long), with filiform posterior process shorter (similar in length as expanded lips part vs. visibly longer), primary axils with smaller guard process, seta-like, and fused to adjacent lateral lip (vs. large, triangular, and scarcely fused to adjacent lateral lip), labial probolae with lateral lips angular (vs. slightly conoid), amphids almost apical (vs. at lip base according the original description, although it could be more apical), longer pharynx (111–137 vs. 62–74 μm long), vulva located slightly more anterior (V=51–63 vs. V=60–63), post-vulval sac lacking lumen along most of its length (vs. with lumen occupying ca. half its length), rectum with cuticular part one third of its length (vs. more than 50%), tail terminus with smaller hyaline part (as long as wide vs. about 1.5 times longer than wide), tail tip biacute (vs. finely rounded), and males absent (vs. frequent).
On the other hand, with respect to A. skrjabini, the new species is very different and clearly distinguished by the morphology of their lip region, with lips and probolae visibly more reduced in A. skrjabini.
Type locality and habitat
Acromoldavicus xerophilus n. sp. was found in two localities from the province of Almería, Spain: i) Salinas de Cabo de Gata (GPS coordinates: latitude 36º45’53.73”N, longitude 2º13’8.10”O), in sand dunes; ii) Tabernas Desert (GPS coordinates: latitude 37º0’4.34”N, longitude 2º27’1.43”O), in sandy soil, both associated with xerophilic vegetation: Arthrocnemum macrostachyum (Moric.) C. Koch, Carduus tenuiflorus Curtis, Caroxylon vermiculatum (L.) Akhani and Roalson, Ephedra fragilis Desf, Helianthemum almeriense Pau, Launaea arborescens (Batt.) Murb, Limbarda crithmoides (L.) Dumort, Limonium insigne (Coss.) Kuntze, Nicotiana glauca Graham, Onthatus maritimus Hoffmanns and Link, Salsola kali L., and Thymelaea hirsuta (L.) Endl.
Type material
Thirty-four females (holotype and paratypes) are deposited in the Nematode Collection of the Department of Animal Biology, Plant Biology and Ecology of the University of Jaén. Two females (paratype) are deposited in the nematode collection of the Swedish Museum of Natural History (Stockholm, Sweden).
Molecular characterization
Three sequences of Acromoldavicus xerophilus n. sp. were obtained: two 18S rDNA fragments, both with 925 bp (PP069740, PP069741), and one 28S rDNA fragment with 1057 bp (PP069742). For 18S rDNA, the two sequences of A. xerophilus n. sp. show 100% similarity, in a fragment in common with 625 bp. With respect to the 28S rDNA, in a fragment in common with 519 bp, the sequence of A. xerophilus n. sp. shows 97.5% similarity (13 bp differences) compared with the sequences of A. mojavicus (DQ145626, AY027536), and 97.3% similarity (14 bp differences) with respect to the sequence of A. skrjabini (AY027535). On the other hand, the two sequences of A. mojavicus and the sequence of Acromoldavicus aff. mojavicus have 100% similarity, which shows that these taxa are probably conspecific.
Discussion
Morphological differences between Acromoldavicus species
According to the morphology of the lip region, the species of the genus Acromoldavicus (Figure 7) can be divided into two groups: a first group with less developed lip region (A. skrjabini) and a second group with more developed lip region (A. mojavicus and A. xerophilus n. sp.). Thus, the skrjabini group is characterized by having lips with acute apical process, slightly laterally curved, smaller vexilla lacking processes, axillar guard process wider at base, triangular, with short elongate tip, and more reduced probolae, almost triangular. On the other hand, the mojavicus group is characterized by having lips with apical process bent toward the oral opening (claw-like) and larger vexilla bearing an elongate process, axillar guard process narrower, triangular, with filiform tip, and larger probolae, pentagonal. In addition, the prostegostom is not expanded toward the stoma lumen in the skrjabini-group (vs. expanded in three tongue-like processes in the mojavicus-group). Comparing both species of the mojavicus group, A. xerophilus n. sp. (Figure 8) shows labial characters slightly more developed than A. mojavicus, female tail more acute (vs. finely rounded in A. mojavicus), and males absent (vs. as frequent as females). With respect to the sexual condition, A. mojavicus and A. skrjabini are amphimictic species, appearing as males frequently, while A. xerophilus n. sp. is, apparently, a parthenogenetic species where males are absent.
Figure 7. Schematic view of the lip region of the Acromoldavicus species. (a) A. skrjabini; (b) A. mojavicus; (c) A. xerophilus n. sp. Iv: ventral primary axil; Isd: subdorsal primary axil; IId: dorsal secondary axil; IIsv: subventral secondary axil; Am: amphid; LAP: lateral axillar process; Lp: lip; LP: labial probola; VAP: ventral axillar process; Vx: vexillum.
Figure 8. Schematic view of the lip region in ventral view of Acromoldavicus xerophilus n. sp. in ventral (left) and lateral (right) views.
With respect to other genera, Acromoldavicus is morphologically related to Scottnema (as reported by Boström Reference Boström1985), showing less modified lips, primary axils with two axillar guard processes (only the sublateral and one ventral process are maintained in Acromoldavicus), having similar pentagonal labial probolae (plesiomorphic condition), and Elaphonema, having lips lacking vexillum but having similar claw-like labial apical processes, axillar guard processes absent, and developing three large oral processes, probably a very modified labial probolae (apomorphic condition).
Phylogenetic position of the genus Acromoldavicus
The phylogenetic analysis based on 18S (Figure 9) and 28S rDNA (Figure 10) fragments clearly shows that the genus Acromoldavicus is monophyletic. However, its relationship with other genera is not clear, appearing in both trees as many clades with low consistency. Thus, the 18S rDNA tree, with an arrangement of genera not well distributed according to morphological relationships, placed the genus Cephalobus Bastian, Reference Bastian1865 as a sister group of Acromoldavicus Nesterov, Reference Nesterov1970, showing 96.24% similarity (25 bp differences) in a fragment in common with 665 bp, although they do not maintain close morphological similarities.
Figure 9. Bayesian inference tree from the newly sequenced Acromoldavicus xerophilus n. sp. based on sequences of the 18S rDNA region. Bayesian posterior probabilities (%) are given for each clade. Scale bar shows the number of substitutions per site.
Figure 10. Bayesian Inference tree from the newly sequenced Acromoldavicus xerophilus n. sp. based on sequences of the 28S rDNA region. Bayesian posterior probabilities (%) are given for each clade. Scale bar shows the number of substitutions per site.
The 28S rDNA tree, with genera well distributed according the morphological relationships, shows that the genus Acromoldavicus is related to species of the genera Nothacrobeles, Paracrobeles, and Spinocephalus, all of them containing species with tessellated cuticles. Thus, in the 28S tree, the closer species are Nothacrobeles abolafiai Mehdizadeh and Shokoohi, Reference Mehdizadeh and Shokoohi2013 with 94.21% similarity (58 bp differences), N. cancellatus (Thorne, Reference Thorne1925) Ruiz-Cuenca and Abolafia, Reference Ruiz-Cuenca and Abolafia2020 with 96.21% similarity (20 bp differences), N. hebetocaudatus Abolafia, Divsalar, Panahi and Shokoohi, Reference Abolafia, Divsalar, Panahi and Shokoohi2014 with 86.72% similarity (137 bp differences), Paracrobeles deserticola Abolafia, Divsalar, Panahi and Shokoohi, Reference Abolafia, Divsalar, Panahi and Shokoohi2014 with 89.53% similarity (108 bp differences), and Spinocephalus tessellatus Abolafia, Hosseinvand and Eskandari, Reference Abolafia, Hosseinvand and Eskandari2021 with 88.76% similarity (72 bp differences). However, Scottnema lindsayae Timm, Reference Timm1971, its more related genus with respect to the morphology of the lip region, appears further in the tree with respect to Acromoldavicus, showing 89.98% similarity (101 bp differences).
List of species of the genus Acromoldavicus Nesterov, Reference Nesterov 1970
The genus Acromoldavicus includes three species (Table 2).
Table 2. Morphometrics of Acromoldavicus species. Measurements in μm and in the form: mean ± standard deviation (range) where appropriate
Demanian indices (de Man Reference de Man1881): a = body length/body diameter; b = body length/pharynx length; c=body length/tail length; c’ = tail length/anal body diameter; V = (distance from anterior region to vulva/body length) x 100.
Type species
Acromoldavicus skrjabini (Nesterov and Lisetskaya, Reference Nesterov and Lisetskaya1965) Nesterov, Reference Nesterov1970
= Acrobeloides skrjabini Nesterov and Lisetskaya, Reference Nesterov and Lisetskaya1965
Other species
Acromoldavicus mojavicus Baldwin, De Ley, Mundo-Ocampo, De Ley, Nadler and Gebre, Reference Baldwin, De Ley, Mundo-Ocampo, De Ley, Nadler and Gebre2001
Acromoldavicus xerophilus n. sp.
Keys to species identification
1a – Lips with small labial expansion …………………………………………….…… skrjabini
1b – Lips with large labial expansion ……….……………………………………………‥……….2
2a – Subdorsal axillar guard processes longer; female tail acute ………………‥ mojavicus
2b – Subdorsal axillar guard processes shorter; female tail slightly biacute …………………………………………………………………………………………… . xerophilus n. sp.
Acknowledgments
The authors appreciate the assistance of technical staff (Amparo Martínez-Morales and Ricardo Oya-Aponte, respectively) and Centro de Instrumentación Científico-Técnica (CICT) from the University of Jaén for supplying equipment for obtaining SEM pictures and DNA sequences.
Financial support
The authors thank the University of Jaén/Caja Rural Jaén Foundation, Spain, for the financial support received for the project entitled “Filogeografía de nematodos rabdítidos (Nematoda, Rhabditida) en ambientes xerofíticos del sur de la peninsula ibérica” (UJA2014/03/01) and the research activities “PAIUJA 2019/2020: EI_RNM02_2019”, “POAIUJA 2021/2022: EI_RNM02_2021” and “POAIUJA 2023/2024: EI_RNM02_2023” of the University of Jaén, Spain.
Competing interest
The authors declare no conflict of interest.
Ethical standard
All procedures contributing to this study comply with the ethical standards of the relevant national and institutional guides on the care and use of laboratory animals.
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