Description of Malenchus sexlineatus n. sp., new records of three known species of Malenchus Andrássy, 1968 (Nematoda: Tylenchidae) and notes on amphidial aperture development

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A new species, Malenchus sexlineatus n. sp., discovered from the Philippines, is described based on morphological and molecular data. The new species is unusual in the genus by having six lateral lines. Malenchus sexlineatus n. sp. is distinguished from M. williamsi, the only other species in the genus with six lateral lines (based on currently available SEM data), by a shorter body of 278 (270-288) vs 452 (425-495) μm, shorter stylet (7.0 (6.2-7.5) vs 11-12 μm), narrower annulations (0.8 (0.7-0.8) vs 1.2-1.6 μm), lateral field comprising one elevated ridge in LM vs six well-separated incisures (resembling the lateral lines in Cephalenchus) in LM, the presence of S-shaped vs straight amphidial apertures, and vulval flaps absent or only one annuli long vs distinct. By having an exceptionally short body, M. sexlineatus n. sp. comes close to M. parvus, M. bryanti and M. acarayensis. However, there are significant differences in the lateral lines, annuli width and most morphometric ratios. Three known species, namely M. exiguus, M. nanellus and M. pachycephalus, all being first records and first representative from China, are characterised by morphological data. The new species was placed in a robustly supported clade containing two other Malenchus spp. and M. exiguus. Interestingly, M. pressulus was placed in a separate, unresolved phylogenetic position. However, the phylogenetic position of these clades could not be resolved within Tylenchidae. The shapes of the amphidial aperture and fovea within Malenchus are also compared and its possible developmental process is illustrated and discussed.

Description of Malenchus sexlineatus n. sp., new records of three known species of Malenchus Andrássy, 1968 (Nematoda: Tylenchidae) and notes on amphidial aperture development

in Nematology



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    LM picture of Malenchus sexlineatus n. sp. (A, E, F), M. nanellus (B, D, H) and M. pachycephalus (C, G, I-M). A-C: Female anterior end; D: Amphidial fovea; E: Lateral view of vulval region; F, G: Female habitus; H: Spicules and protruding cloacal lips; I: Vulva and spermatheca; J: Annules on female tail; K: Crenate female lateral lines; L: Ventral view of vulva; M: Female ventral view (arrow showing prophasmid). (Scale bars: A-E, H-M = 10 μm; F, G = 50 μm.)

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    Malenchus sexlineatus n. sp. from the Philippines, female holotype and male paratype (A, B, F-H, L-P) and Chinese population of M. nanellus Siddiqi, 1979 (C-E, I-K). A: Female anterior body; B: Male anterior body; C, D: Female anterior body; E: Male tail; F: Female stylet; G: Male tail showing spicule, gubernaculum and bursa; H, I: Female reproductive system, showing sunken vulva, epiptygmata, thickened vaginal wall and PUS; J: Posterior male body showing spicule, gubernaculum; K, L: Female habitus; M: Male habitus showing dorsally bent tail; N: Tail tip; O: Cross-section of body showing lateral field as single elevated ridge; P: Annules. (Scale bars: A-E, G-M = 10 μm; F = 20 μm; N-P: diagrammatic.)

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    SEM of female Malenchus sexlineatus n. sp. from the Philippines. A: Lip region; B: En face view; C: Ventral view of vulva showing epiptygmata; D: Anus (an = opening of anus); E: Tail; F: Lateral view of vulva (pp = prophasmid); G: Six incisures in lateral region; H: Hook-shaped tail tip. (Scale bars: A-D, F-H = 1 μm; E = 5 μm.)

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    Bayesian strict consensus phylogeny highlighting the phylogenetic position of M. sexlineatus n. sp. in relation with other relevant sequences from GenBank based on the D2-D3 domain of LSU rDNA sequences. Branch support is indicated in following order: PP value in BI analysis/BS value from ML analysis. New sequences generated in this study are highlighted in bold.

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    SEM of female and juvenile of Malenchus nanellus from China, and the possible development process of amphidial aperture. A: En face view of female showing oval hole in anterior part of amphidial aperture; B: Anterior part of female; C: Lateral view of female lip region; D: Lip region of juvenile; E: Possible development process of amphidial aperture. (Scale bars: A, C, D = 10 μm, B = 50 μm.)

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    LM picture of Malenchus exiguus (A, B, G, H, J, K) and Malenchus sp. (C-F, I). A, B: Female anterior body; C: Ventral view of female anterior body (arrow showing amphidial fovea); D: Female reproductive system showing sunken vulva, thicken vaginal wall; E: Female lip region (arrow showing amphidial aperture); F: Prophasmid (arrow); G: Lateral region with offset ridge; H: Female reproductive system showing part of ovary, spermatheca, uterus, vagina and sunken vulva; I: Ventral view of vulva; J, K: Female body habitus. (Scale bars: A-G, I = 10 μm; H, J, K = 100 μm.)

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    Malenchus exiguus (A, B, D, E-G, I, J, M-O, R) and Malenchus sp. (C, H, K, L, P, Q). A: Female anterior body; B: Male anterior body; C: Ventral view of female anterior body, arrow showing elevated lateral ridge; D: Male reproductive system; E: Female reproductive system; F: Spermatids from vesicula seminalis; G: Sperm cells from vesicula seminalis; H: Female reproductive system; I: Male habitus; J-L: Female habitus; M: Male median bulb showing elongated valvular apparatus; N: Female median bulb showing round valvular apparatus; O, P: Folded cuticle; Q: Lateral view of lip region showing amphidial aperture and fovea; R: Male tail. (Scale bars: A, B = 10 μm; C, D, E, H, R = 20 μm; I-L = 100 μm; M, N, Q = 5 μm; F, G, O, P = diagrammatic.)

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    Comparing alternative hypotheses using AU and SH test. The topological schemas (hypotheses) are compared with the originally obtained topology (Fig. 4). Clades containing Malenchus species are highlighted in grey. A: The hypothesis of paraphyly of Malenchus as robustly supported (BS = 99) in the analysis of Yaghoubi et al. (2015); B: The hypothesis of monophyly of Malenchus. ΔlnL: the Log likelihood difference of the two alternative hypotheses. The two hypotheses are less likely than the original topology, but only hypothesis B can be significantly rejected.

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    3D models of the lip region of the two subgenera of Malenchus. A-D: S-shaped amphidial aperture, subgenus Malenchus; E-H: Straight amphidial aperture, subgenus Telomalenchus; I: Lateral view of amphidial fovea.

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