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Mountainous millipedes in Vietnam. II. A conspicuous Tylopus species from Northern Vietnam (Diplopoda, Polydesmida, Paradoxosomatidae)
expand article infoAnh D. Nguyen§, Katsuyuki Eguchi|
‡ Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, Hanoi, Vietnam
§ Graduate University of Science and Technology, Hanoi, Vietnam
| Tokyo Metropolitan University, Hachioji-shi, Japan
Open Access

Abstract

A conspicuous Tylopus species is described from Northern Vietnam, namely T. helicorthomorphoides sp. nov. The new species is clearly diagnosed by the gonopodal solenophore completely sheathing the solenomere, both being coiled three times, and the absence of spine z and process h of the gonopod. Fragments of the COI and 16S rRNA genes were extracted, and the phylogenetic analysis also supports the new species.

Keywords

Biodiversity, COI, 16S rRNA, mountain fauna, taxonomy

Introduction

The genus Tylopus was established by Jeekel (1968) with type species Agnesia sigma Attems, 1953. Jeekel (1965, 1968) diagnosed this genus by having well-developed paraterga, first pair of legs without modifications, the presence of tibial and tarsal brushes and adenostyles (= ventral tubercles on the podonomeres), gonopod with somewhat distally enlarged femorite, a distinctly laterally demarcated postfemoral region, postfemorite with 1–3 processes, and both lamina medialis and lamina lateralis well developed. The genus was extensively revised, and morphological terms for the genus Tylopus were standardized by Golovatch and Enghoff (1993) and updated by Likhitrakarn et al. (2010, 2016).

Tylopus is considered the most species-rich genus within the family Paradoxosomatidae Daday, 1889. Currently, it contains 77 species (Golovatch and Semenyuk 2021; Likhitrakarn et al. 2021; Sierwald and Spelda 2021) distributed from Southern China down to Indonesia and Malaysia, and from Myanmar to Vietnam. They are seemingly dominant in Southeast Asia, especially in Thailand, Laos, and Vietnam, although this may be due to research bias. In Vietnam, 21 species were recorded so far (Attems 1938, 1953; Golovatch 1984; Korsós and Golovatch 1989; Golovatch and Enghoff 1993; Nguyen 2012; Golovatch and Semenyuk 2018, 2021), all of which completely agree with the typical diagnosis for the genus.

As a continuation of our contributions to the millipede fauna of mountainous regions of Vietnam, this work aims to describe a conspicuous Tylopus species from northern Vietnam and to discuss relationships between Vietnamese Tylopus species.

Materials and methods

Material was collected from two localities in Northern Vietnam, Tam Dao National Park and Bac Me Natural Reserve (Fig. 1), and preserved in 90% ethanol. Specimens were observed under an Olympus SZX10 microscope. Images were taken at various focal planes using a Nikon imaging system (Nikon-Br) coupled with a SMZ800N Nikon stereomicroscope. Images were stacked using Helicon Focus version 7.0 and assembled in Adobe Photoshop CS6.

Figure 1. 

Distribution of Tylopus helicorthomorphoides sp. nov. Tam Dao (Red triangular); Bac Me (Red circle)

Total DNA was extracted from several midbody legs using the QIAGEN DNeasy Blood & Tissue Kit. Fragments of the mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA genes were amplified using two pairs of primers: COI-1F (5’-ACTCTACTAATCATAAGGAT-3’) and COI-1R (5’-TAAACCTCCGGGTGACCAA-3’), 16S-1F (5’-CCGGTTTGAACTCAGATCA-3’) and 16S-1R (5’-TGACTGTTTAGCAAAGACAT-3’). The amplification protocol followed a previously published method by Nguyen et al. (2017). Each successfully amplified and sequenced fragment was assembled using ChromasPro v.2.1.8 and confirmed by BLAST 2.6.0+ searches (Zhang et al. 2000).

All confirmed sequences were aligned using Cluster X ver.2.0 (Larkin et al. 2007), and ambiguous nucleotide sites and gaps were removed using MEGA X (Kumar et al. 2018). The COI sequences were translated into amino acids for confirmation using transversion code in MEGA X. The concatenated dataset (COI+16S) was created from the COI dataset and 16S rRNA dataset using the software GBLOCK 0.91b.

The nucleotide frequencies were statistically calculated using MEGA X. The final dataset contains 956 bp, including 586 bp of the COI gene and 370 bp of the 16S rRNA gene. It has nucleotide frequencies of 26.1, 38.3, 17.5, and 18.0 for A, T, G, and C, respectively. The GC content accounts for 35.5% of total nucleotides. The dataset has 324 parsimony-informative and 403 variable sites.

The phylogenetic tree was reconstructed using the Maximum Likelihood (ML) analysis with the best model resulting the ModelFinder (Kalyaanamoorthy et al. 2017), performed in IQTREE ver.1.6.2 for Windows (Minh et al. 2020). Models with the lowest BIC scores (Bayesian Information Criterion) are considered to describe the best substitution pattern. As a result, the model TIM3+F+G4 was selected (BIC score of 12506.102; -LnL = 6033.252).

All specimens, including holotype and paratypes and DNA vouchers, have been deposited in the Department of Soil Ecology, Institute of Ecology and Biological Resources (IEBR), Vietnam Academy of Science and Technology, Hanoi, Vietnam. A total of 24 new sequences were deposited in GenBank, with accession numbers as presented in Table 1.

Table 1.

Analyzed species, locality data, deposition voucher numbers, and GenBank accession numbers. Accession numbers in bold font are new sequences.

No Species Locality Voucher 16S rRNA COI
1 Tylopus crassipes Golovatch, 1984 Sapa, Lao Cai IEBR- Myr 92 OM978927 KX096920
2 Tylopus hilaroides Golovatch, 1984 Cuc Phuong, Ninh Binh IEBR- Myr 543 OM978921 MW384914
3 Tylopus hilaroides Golovatch, 1984 Cuc Phuong, Ninh Binh IEBR- Myr 198 KX755588 MW384918
4 Tylopus hilaroides Golovatch, 1984 Cuc Phuong, Ninh Binh SVE- Myr 149 OM978930 MW384905
5 Tylopus hilaroides Golovatch, 1984 Cuc Phuong, Ninh Binh SVE- Myr 173 OM978931 MW384904
6 Tylopus hilaroides Golovatch, 1984 Tam Dao, Vinh Phuc SVE- Myr 55 OM978932 MW384903
7 Tylopus nodulipes (Attems, 1953) Huong Son, Ha Tinh IEBR- Myr 105 OM978913 MW384919
8 Tylopus nodulipes (Attems, 1953) Minh Hoa, Quang Binh IEBR- Myr 557 OM978924 MW384912
9 Tylopus roseiparaterga Nguyen, 2012 Ba Vi, Ha Noi SVE- Myr 70 OM978933 MW384902
10 Tylopus sapaensis Nguyen, 2012 Sa Pa, Lao Cai IEBR- Myr 93 OM978928 MW384908
11 Tylopus spinisternus Nguyen, 2012 Bi Doup – Nui Ba, Lam Dong IEBR- Myr 234 OM978915 MW384916
12 Tylopus sp.1 Ba Vi, Ha Noi SVE- Myr 73 OM978934 MW384901
13 Tylopus sp.1 Ba Vi, Ha Noi SVE- Myr 74 OM978935 MW384900
14 Tylopus sp.2 Phong Nha – Ke Bang, Quang Binh IEBR- Myr 210 OM978914 MW384917
15 Tylopus sp.2 Phong Nha – Ke Bang, Quang Binh IEBR- Myr IPE6 OM978929 MW384907
16 Tylopus sp.3 Sa Pa, Lao Cai IEBR- Myr 556 OM978923 MW384913
17 Tylopus sp.4 Son Dong, Bac Giang IEBR- Myr 509 OM978919 MW384915
18 Tylopus helicorthomorphoides sp.nov. Tam Dao, Vinh Phuc IEBR- Myr 603 OM978925 MW384910
19 Tylopus sp.7 Muong Nhe, Dien Bien IEBR- Myr 617 OM978926 MW384909
20 Oxidus gigas (Attems, 1953) Sapa, Lao Cai IEBR-Myr 113 KX755581 KX096921
21 Oxidus gigas (Attems, 1953) Duc Xuan, Ha Giang IEBR-Myr 516 OM978920 KX096928
22 Oxidus riukiaria (Verhoeff, 1940) Ryukyu, Japan IEBR-H500 OM978918 KX096926
23 Oxidus riukiaria (Verhoeff, 1940) Ryukyu, Japan IEBR-H500J KX755583 KX096927
24 Oxidus gracilis (C.L. Koch, 1847) Taiwan IEBR- Myr 549 OM978922 KX096931
25 Oxidus gracilis (C.L. Koch, 1847) Ryukyu, Japan IEBR- Myr 466 OM978916 KX096924
26 Oxidus gracilis (C.L. Koch, 1847) Ryukyu, Japan IEBR- Myr 471 OM978917 KX096925
27 Oxidus gracilis (C.L. Koch, 1847) USA IEBR-Myr USA KX096919 KX096931
28 Sellanucheza grandis (Golovatch, 1984) Xuan Son, Phu Tho IEBR-Myr 177 KX755584 KR818296
29 Sellanucheza hoffmani Nguyen, 2011 Phong Nha – Ke Bang, Quang Binh IEBR- Myr 182 KX755585 KR81829
30 Sellanucheza variata (Attems, 1953) Duc Xuan, Ha Giang IEBR- Myr 515 KX755586 OM919709
Antheromorpha pumatensis Nguyen, 2018 Pu Mat, Nghe An IEBR- Myr IPE3 MG669559 MG669372

Taxonomy

Order Polydesmida

Family Paradoxosomatidae Daday, 1889

Genus Tylopus Attems, 1953

Tylopus helicorthomorphoides sp. nov.

Figs 1, 2, 3, 4, 5

Material examined

Holotype. Vietnam • 1 male; Vinh Phuc Province, Tam Dao National Park, on the way to Tam Dao 2; 1,100 m a.s.l.; 25 Feb. 2017; Anh D. Nguyen leg.; natural forests; IEBR-Myr 603H.

Paratypes. Vietnam • 2 females; same data as for holotype; IEBR-Myr 603P • 1 male; Vinh Phuc Province, Tam Dao National Park, on way to TV tower; 21.46065°N, 105.64863°E; 1,081 m a.s.l.; 10 Dec. 2019; Hoang Quang Duy leg.; natural forests; IEBR-Myr 876.

Non-type. Vietnam • 1 male; Ha Giang Province, Bac Me Natural Reserve, Minh Ngoc commune, Lung Can village; 22.71814°N, 105.17997°E; 361 m a.s.l.; 12–13 Dec. 2018; Anh D. Nguyen leg.; bushes (IEBR-Myr 809).

Diagnosis

The new species distinctly differs from its congeners in having a three-times spiraled solenophore of the gonopods and postfemoral lamella l present while spine z and process h totally absent. The new species is slightly similar to its congener T. strongylomoides (Korsórs & Golovatch, 1989), from the same locality (Tam Dao National Park), in having a twisted solenophore and solenomere. However, the new species obviously differs from T. strongylosomoides in having a more strongly coiled solenophore and solenomere (3× vs 1.5×).

Regarding the gonopod conformation, the new species is somewhat similar to species of the genus Helicorthomorpha in the twist of both the solenophore and solenomere. However, the postfemoral region of Helicorthomorpha members is more elaborate, twisted, and carries no additional processes, whereas that of the new species is spiraled or coiled rather than twisted, and has a postfemoral lamella.

Etymology

The species epithet, helicorthomorphoides, is used to emphasize the similarity of the gonopod solenophore between the new species and those of the genus Helicorthomorpha.

Description

Body length ~ 14.4 mm (male) and 14.9 mm (female). Width of midbody pro- and metazona ~ 1.2 mm (male), 1.6 mm (female) and 1.6 mm (male), 1.9 mm (female), respectively.

Body generally brownish yellow or darkish yellow except antennomere 7 and metaterga with a darker, median, V-shaped region (or median triangular-shaped area on metaterga) (Figs 24).

Figure 2. 

Tylopus helicorthomorphoides sp. nov. Holotype (IEBR-Myr 603H). Anterior part of body, lateral view (A) dorsal view (B) ventral view (C) midbody segments, lateral view (D).

Head (Fig. 2B, C) slightly smaller than collum, labroclypeous region densely setose. Epicranial suture clearly distinct, dividing frons into two equal parts, with 2+2 setae along suture. Frons convex. Antenna (Fig. 2A–C) short, reaching to approximately tergum 2 laterally. Antennomere 1=7<2=3=4=5<6; antennomere 6 largest, obviously clavate.

Collum (Fig. 2B) oval-shaped, surface smooth, without granulates or tubercles, but with 2+2 setae near anterior margin and 2+2 setae in intermediate area. Paratergum well developed, subtriangular, with broad corner.

Body segments 3<4<2=5–17, thereafter gradually tapering towards telson. Prozonae and metazonae clearly divided by deep, striated waists. Prozonae smooth, shining, yellowish brown, with a median, broad, longitudinal yellow stria (Figs 2B, 3A). Metazonae (Figs 2B, 3A) smooth, shining, with 2+2 setae near anterior margin, two lateral spotted areas, and 2+2 or 3+3 oblong knobs near posterior margin. These knobs more obvious on posterior segments.

Figure 3. 

Tylopus helicorthomorphoides sp. nov. Holotype (IEBR-Myr 603H). Midbody segments, dorsal view (A) posterior part of body, lateral view (B) dorsal view (C) ventral view (D).

Metatergal sulcus starting on segment 4 but clearly present from segment 5, nearly reaching base of paraterga (Fig. 2B). Axial line distinct.

Paraterga (Figs 2A, B, D, 3A–C) well developed, wing-shaped, with at least one setiferous incision near anterior, broadly round corner; caudal corner acute, more pointed from mid-body segment onwards, but never reaching following segment. Caudal corner of paraterga 17–19 very pointed, spine-like (Fig. 3C, D).

Ozopores located inside round hollows at the caudolateral sides of paraterga 5, 7, 9, 10, 12, 13, and 15–19 (Figs 2A, D, 3B).

Pleurites (Figs 2A, D, 3B) smooth, not granulated. Pleurosternal carinae (Fig. 2A) present until segment 8, with a small tubercle-like projection, then gradually reduced or missing on subsequent segments.

Telson (Figs 3C, D, 4A). Epiproct strongly concave, forming two long lateral tubercles. Hypoproct sub-trapeziform, with two separated distolateral setiferous knobs.

Sterna. Cross impression distinct. Sternum 5 with a large rectangular lamina between coxae 4 (Fig. 4B).

Figure 4. 

Tylopus helicorthomorphoides sp. nov. Holotype (IEBR-Myr 603H). Epiproct, paraproct and hypoproct (A) sternal process between coxae 4, ventral view (B) leg 6 (C) gonopods, ventral view (D).

Leg short, ~ 1.5× as long as midbody height. Prefemora swollen dorsally. Tarsal brushes present till legs 21, then gradually thinner and absent on subsequent legs. Adenostyles present on postfemora and tibiae, each with a small knob/tubercle (Fig. 4C).

Gonopod suberect, simple (Figs 4D, 5, 6). Coxite short, with sparsely setose distoventral part. Telopodite long and erect. Prefemorite densely setose, separated from femorite by an oblique sulcus laterally. Femorite somewhat enlarged distally and slightly twisted, without modifications or additional processes. Postfemoral region consisting of a solenomere and a solenophore, both completely coiled 3×; lamina l present, spine z and process h missing. Seminal groove running entirely on mesal side of femorite, then entering flagelliform solenomere completely sheathed by solenophore. Tip of gonopod strongly bifid.

Figure 5. 

Tylopus helicorthomorphoides sp. nov. Holotype (IEBR-Myr 603H). Right gonopod, mesal view (A) ventral view (B) dorsal view (C) lateral view (D). Scale bar: 0.1 mm. co = coxite, pfe = prefemorite, fe = femorite, sl = solenomere, sph = solenophore, sg = seminal groove, l = lamella l.

Genetic distance

The COI Kimura 2-Parameter (K2P) distance between the new species and other Tylopus species was reported in Anh et al. (2021). The distance was from 12.2% to 15.6%. This distance was obviously narrower than the distances between Sphaerobelum species (from 20.2% to 24.4%) (Zhao et al. 2020), but more likely similar to the distances between Glomeris species (from 11.5% to 17.1%) (Wesener 2015).

Figure 6. 

Tylopus helicorthomorphoides sp. nov. Holotype (IEBR-Myr 603H). Right gonopod, mesal view (A) dorsal view (B) ventral view (C) lateral view (D). Scale bar: 0.1 mm. co = coxite, pfe = prefemorite, fe = femorite, sl = solenomere, sph = solenophore, sg = seminal groove, l = lamella l.

Phylogenetic analysis

The twenty included samples of Tylopus members were divided into two different lineages (Fig. 7). The first lineage, Tylopus I, consisting of three species, T. hilaroides, T. sapaensis, and Tylopus sp.1, was a sister clade of the genus Oxidus with 95% bootstrap support.

Figure 7. 

Phylogenetic diagram inferred from the 956 bp COI-16S rRNA dataset using Maximum Likelihood analysis. Numbers shown at nodes are bootstrap values.

The second lineage, Tylopus II, was clearly separated from the clade Oxidus + Tylopus I with high bootstrap support (97%). The new species, T. helicorthomorphoides sp. nov., was positioned in this lineage and is closely related to Tylopus sp. 4 (IEBR-Myr 509), but with low bootstrap support (49%). In addition, the relationship between Tylopus species in the second lineage was very poorly supported (bootstrap less than 70%), except the clade T. crassipes + T. roseiparaterga, with a bootstrap value of 90%.

Discussion

Both Jeekel (1965) and Golovatch and Enghoff (1993) agreed that the gonopod solenophores sheath the flagelliform solenomere for its greater part, curving caudad first, then laterad and finally cephalad in Tylopus members. In the new species, the solenophore and solenomere morphology agree with this statement but are completely coiled three times, the gonopod spine z and process h are absent, whereas only postfemoral lamina l is present. Our phylogenetic analysis also supports the taxonomic position of the new species within the genus Tylopus.

The genus Tylopus is, phylogenetically, divided into two clades as reported above. This also agrees with the results presented by Anh et al. (2021) using only a fragment of the COI gene. It is, therefore, suggested that the genus Tylopus needs to be revised accordingly, using both morphological and molecular data. This case may be similar to that of the genus Desmoxytes Chamberlin, 1923, which was recently intensively revised by Srisonchai et al. (2018a, 2018b, 2018c, 2018d). Finally, the genus Hylomus Cook & Loomis, 1924 has been re-validated, with three new genera proposed for other so-called Desmoxytes members (Srisonchai et al. 2018a, 2018b, 2018c, 2018d). Furthermore, the relationship between Tylopus species was very poorly supported (less than 70% bootstrap value), especially within the second lineage. More samples and species are required for a better analysis.

The genus Tylopus has been found in both lower and higher lands in northern Vietnam, but it has only been recorded in higher lands in southern Vietnam, and has never been found in the Mekong delta (Nguyen 2012; Golovatch and Semenyuk 2018, 2021). The distributional pattern of this genus in Vietnam is similar to that in Thailand, where Tylopus species are mostly found in mountainous regions with altitudes of more than 500 m in northern and central Thailand (Likhitrakarn et al. 2010). The highest recorded altitude is 2,300m in Ngoc Linh Mt. (Vietnam) for Tylopus hilaris (Attems, 1937) and T. phanluongi Nguyen, 2012. Furthermore, as mentioned by Nguyen et al. (2019, 2021), the mountainous region of Vietnam harbors a rich biodiversity in Vietnam, but it is far from completely known because access to the region is difficult and intensive surveys are still lacking.

Conclusion

With the new species described herein, the number of Tylopus species known for Vietnam increases to 22. However, this number is still far from representing the true diversity of the genus in Vietnam. More intensive surveys will reveal more new discoveries, especially in the diverse high mountainous regions of Vietnam, which remain underexplored.

Acknowledgements

This research was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED), under grant number 106.05-2019.320 to Anh D. Nguyen. The work was also supported by the Tokyo Metropolitan University Fund for TMU Strategic Research (Leader: Prof. Noriaki Murakami; FY2020-FY2022).

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Supplementary material

Supplementary material 1 

The COI-16S rRNA dataset

Anh D. Nguyen, Katsuyuki Eguchi

Data type: DNA data

Explanation note: The COI-16S rRNA dataset contains 956 bp, including 586 bp of the COI gene and 370 bp of the 16S rRNA gene.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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