Research Article |
Corresponding author: Shiuh-Feng Shiao ( sfshiao@ntu.edu.tw ) Academic editor: Andreas Schmidt-Rhaesa
© 2020 Ming-Chung Chiu, Chin-Gi Huang, Wen-Jer Wu, Zhao-Hui Lin, Hsuan-Wien Chen, Shiuh-Feng Shiao.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Chiu M-C, Huang C-G, Wu W-J, Lin Z-H, Chen H-W, Shiao S-F (2020) A new millipede-parasitizing horsehair worm, Gordius chiashanus sp. nov., at medium altitudes in Taiwan (Nematomorpha, Gordiida). ZooKeys 941: 25-48. https://doi.org/10.3897/zookeys.941.49100
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Gordius chiashanus sp. nov., a newly described horsehair worm that parasitizes the Spirobolus millipede, is one of the three described horsehair worm species in Taiwan. It is morphologically similar to G. helveticus Schmidt-Rhaesa, 2010 because of the progressively broadening distribution of bristles concentrated on the male tail lobes, but it is distinguishable from G. helveticus because of the stout bristles on the mid-body. In addition, a vertical white stripe on the anterior ventral side and areoles on the inside wall of the cloacal opening are rarely mentioned in other Gordius species. Free-living adults emerged and mated on wet soil under the forest canopy in the winter (late November to early February) at medium altitudes (1100–1700 m). Mucus-like structure covering on the body surface, which creates a rainbow-like reflection, might endow the worm with high tolerance to dehydration. Although Gordius chiashanus sp. nov. seems to be more adaptive to the terrestrial environment than other horsehair worm species, cysts putatively identified as belonging to this hairworm species found in the aquatic paratenic host, Ephemera orientalis McLachlan, 1875, suggest the life cycle of Gordius chiashanus sp. nov. could involve water and land. The free-living adults emerged from the definitive hosts might reproduce in the terrestrial environment or enter an aquatic habitat by moving or being washed away by heavy rain instead of manipulating the behavior of their terrestrial definitive hosts.
definitive host, immature stage, parasitic life cycle, terrestrial adaptation
In addition to the two previously described species of horsehair worm (
The definitive hosts of Gordius cover a wide range of arthropod taxa. Although many host records might be questionable because the genus Gordius (G. aquaticus Linnaeus, 1758) had been used to represent the entire members of horsehair worms, Gordius species might parasitize several insect orders, Chilopoda, Diplopoda, and Araneae as their definitive hosts (
Free-living adults of Gordius chiashanus sp. nov. are frequently found in foggy forests situated at altitudes of 1100–1700 m in Taiwan. Their taxonomic status was first examined in the present study by using a description of morphology and phylogenetic comparison of partial mitochondrial DNA cytochrome oxidase subunit I (mtDNA-COI) genes. The definitive host was determined using worms with high sequence similarity collected from the round-backed millipede, Spirobolus sp. nov. (Hsu and Chang, unpublished). Egg strings and larvae were obtained by allowing a field collected adult free-living female worm to oviposit egg string in the laboratory. The cysts which morphologically similar to the laboratory-reared larvae were collected from the field-collected mayfly naiad, Ephemera orientalis McLachlan, 1875. Based on our field observations on adult free-living worms, cysts and their hosts, along with our laboratory observations of non-adult stages for this gordiid species, we suggest the possible life history of Gordius chiashanus sp. nov.
Horsehair worm samples were identified visually and collected from the ground. In total, 21 free-living adults (17 male and 4 female adults) were collected for morphological examination and DNA sequencing (detailed information provided in Table
Free-living adults. Fragments (approximately 0.5 cm in length) of the anterior end, mid-body, and posterior end of the preserved samples were examined and photographed using a stereomicroscope (Leica S8 APO, Leica, Wetzlar, Germany), dehydrated using a series of ethanol and acetone solutions (95% and 100% ethanol (twice) and ethanol/acetone mixtures of 2:1, 1:1, 1:2, and 0:1), dried to the critical point, coated by being sputtered with gold, and examined using a scanning electronic microscope (SEM) (JEOL JSM-5600, Tokyo, Japan) at magnifications ranging from 100× to 15,000×.
Eggs and larvae. Eggs and newly hatched larvae (living or treated with hot water (> 80 °C)) were examined and photographed on microslides by using a compound microscope (Olympus BH-2, PM-10AD, Olympus, Tokyo, Japan) at magnifications of 200× and 400×. The eggs examined using the SEM were first fixed using a solution of 75% alcohol, dehydrated, dried to the critical point, and coated with gold sputter. The eggs and larvae were examined at a magnification of 500×. ImageJ 1.47 was used for all morphological measurements (
Cysts in the paratenic host. The mayflies preserved in 75% alcohol were first treated with Nesbitt’s fluid for 15–20 min at 40 °C and a 0.1% KOH solution for 5 min at 40 °C to ensure that the cuticle and muscles had become transparent (
Genomic DNA from a 1-cm mid-body section of each worm was extracted using an ALS Tissue Genomic DNA Extraction Kit (Pharmigene, Kaohsiung, Taiwan). The partial cytochrome c oxidase subunit I (COI) sequence was amplified using universal primers (LCO1490 and HC02198) (
In addition to sequencing three free-living adult worms and six immature worms recovered from millipede hosts (242–457 high-quality base pairs), we obtained high-quality CO1 sequences (>500 base pairs) from 18 adult free-living individuals to be used in our phylogenetic analysis and estimates of intraspecific genetic distances. Pairwise distance matrices of COI sequence data were calculated using the Kimura 2-parameter model. A phylogenic tree was reconstructed using the maximum likelihood method by using the General Time Reversible model with the addition of invariant sites and a gamma distribution of rates across sites. For phylogenic analysis, the COI sequences were first aligned using CLUSTALX 2.0.10 (
Seasonal occurrence of free-living adults was estimated by counting (and removing) free-living adults (living or dead) on the ground in Dinghu, Alishan township, Chiayi county, Taiwan (23°29'29.10"N, 120°43'19.00"E) between October 2017 and May 2018.
Dinghu (23°29'29.10"N, 120°43'19.00"E), Alishan township, Chiayi county, Taiwan (holotype). Paratypes were collected from Dasyueshan (Heping district, Taichung city), Xitou (Lugu township, Nantou county), Shihjhuo, Fenqihu (Zhuqi township, Chiayi county), Dinghu (Alishan township, Chiayi county), and Hongshi forest road (Haituan township, Taitung county). Table
Partial bodies of the holotype and allotype were deposited at the National Museum of Natural Science, Taichung, Taiwan. Paratypes were deposited at the National Museum of Natural Science, Taichung, Taiwan and Lake Biwa Museum, Shiga, Japan (Table
Collection date | GenBank no. | Locality | Longitude and latitude | Collector | Depository | Sex | Status | Length (mm) |
---|---|---|---|---|---|---|---|---|
20-XI-2017 | MN784831 1 | Dasyueshan (Heping, Taichung, Taiwan) | 24°14'47.90"N, 120°56'06.80"E | Ta-Chih Chen | NMNS | M | Free-living adult | 430 |
26-XI-2008 | MN784832 | Hongshi trail (Haituan, Taitung, Taiwan) | 23°04'14.50"N, 121°07'58.30"E | Po-Yen Chen | NMNS | M | Free-living adult | 744 |
22-I-2008 | MN784841 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°29'01.70"N, 120°42'05.90"E | Yu-Hsuan Tsai | NMNS | M | Free-living adult | 860 |
9-II-2007 | MN784833 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°29'01.70"N, 120°42'05.90"E | Yu-Hsuan Tsai | NMNS | F | Free-living adult | 707 |
8-XII-2017 | MN784819 | Dinghu (Alishan, Chiayi, Taiwan) | 23°29'29.10"N, 120°43'19.00"E | Ming-Chung Chiu | LBM | M | Free-living adult | 771 |
8-XII-2017 | MN784820 | Dinghu (Alishan, Chiayi, Taiwan) | 23°29'29.10"N, 120°43'19.00"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 734 |
8-XII-2017 | MN784821 | Dinghu (Alishan, Chiayi, Taiwan) | 23°29'29.10"N, 120°43'19.00"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 726 |
17-XII-2013 | MN784822 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | LBM | M | Free-living adult | 803 |
17-XII-2013 | MN784823 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | LBM | M | Free-living adult | 756 |
17-XII-2013 | MN784824 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | NMNS | M | Free-living adult | 594 |
17-XII-2013 | MN784825 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | NMNS | M | Free-living adult | 383 |
17-XII-2013 | MN784826 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | NMNS | M | Free-living adult | 676 |
17-XII-2013 | MN784827 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Hua-Te Fang | NMNS | M | Free-living adult | 474 |
18-XII-2017 | MN784828 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 749 |
18-XII-2017 | MN784829 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Ming-Chung Chiu | NMNS | F | Free-living adult | 666 |
18-XII-2017 | MN784830 | Fenqihu (Zhuqi, Chiayi, Taiwan) | 23°30'12.70"N, 120°41'36.00"E | Ming-Chung Chiu | NMNS | F | Free-living adult | 717 |
18-XII-2016 | MN784816 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Ming-Chung Chiu | LBM | M | Free-living adult | 498 |
18-XII-2016 | MN784817 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 403 |
18-XII-2016 | MN784818 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Ming-Chung Chiu | LBM | F | Free-living adult | 549 |
9-II-2008 | MN784842 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 572 |
10-XII-2011 | MN784840 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Ming-Chung Chiu | NMNS | M | Free-living adult | 502 |
17-III-2019 | MN784839 | Xitou (Lugu, Nantou, Taiwan) | 23°40'21.30"N, 120°47'27.50"E | Zhao-Hui Lin | NMNS | - | Dead worm in host | - |
23-VII-2018 | MN784834 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°29'01.70"N, 120°42'05.90"E | Yu-Wei Li | NMNS | - | Immature worm | 660 |
28-VII-2018 | MN784835 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°28'22.60"N, 120°41'42.80"E | Yu-Wei Li | NMNS | - | Immature worm | 894 |
28-VII-2018 | MN784836 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°28'22.60"N, 120°41'42.80"E | Yu-Wei Li | NMNS | - | Immature worm | 420 |
28-VII-2018 | MN784837 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°28'22.60"N, 120°41'42.80"E | Yu-Wei Li | NMNS | - | Immature worm | 442 |
28-VII-2018 | MN784838 | Shihjhuo (Zhuqi, Chiayi, Taiwan) | 23°28'22.60"N, 120°41'42.80"E | Yu-Wei Li | NMNS | - | Immature worm | 426 |
Spirobolus sp. nov. (Hsu and Chang, unpublished) (Diplopoda: Spirobolidae) (Fig.
The specific name is the combination of chia, referring to the place (Chiayi county) where the first sample was found, and shan, referring to the Chinese word for “mountains.” The word chia is also in memory of our friend, Chia-Chih Lin, who died in an accident in a field experiment.
Male adults (N = 11) (Figs
Anterior end of male Gordius chiashanus sp. nov. A stereomicroscopic image of the ventral side of the anterior end showing a white cap, dark-brown collar, and vertical white stripe on the ventral side B, C SEM images of the anterior end surface that is (B) smooth with scattered short bristles and (C) wrinkled D close-up view of the dotted square in C showing the short bristles (arrows) covered by a wrinkled structure. Scale bars: 2 mm (A), 200 μm (B–D).
Anterior end columnar and spherical; anterior tip white (white cap) with a dark -brown collar and a vertical white stripe on the ventral side (Fig.
Cuticle in mid-body ornamented with a dorsal and a ventral dark pigment line; white spots scattered across entire body surface (Figs
Posterior end divided into two tail lobes (Fig.
Posterior end of male Gordius chiashanus sp. nov. A stereomicroscopic image of the posterior end B–D SEM images of (B) overview of the posterior end with bristles concentrated on the (C) lobe tips (arrow), and (D) inner side of the lobe tips and the formation of a bristle field on each tail lobe posterior to the tips of the postcloacal crescent (arrows) E cloacal opening with areoles on the inside wall. Scale bars: 1 mm (A), 500 μm (B), 200 μm (C–D), 50 μm (E).
Mid-body of male Gordius chiashanus sp. nov. A, B SEM images of (A) cuticle in the mid-body with scattered short bristles (arrows) and (B) close-up view of a short bristle C, D white spots and dorsal and ventral dark pigmented line examined using (C) a compound microscope and (D) a stereomicroscope. Scale bars: 1 mm (A, C, D), 5 μm (B).
Female adults (N = 4) (Figs
Female Gordius chiashanus sp. nov. A, B anterior end examined using a (A) stereomicroscope and (B) SEM C–E posterior end with the terminal view examined using a (C) stereomicroscope and (D) SEM, and the (E) lateral view examined using a stereomicroscope F, G mid-body examined using a (F) stereomicroscope and (G) compound microscope. Co, cloacal opening. Scale bars: 1 mm (A, F, G), 200 μm (B–D).
Field observation of Gordius chiashanus sp. nov. A hazy appearance (arrows) surrounding the body surface in hot water B spermatophore (arrow) on a female collected on the surface of the soil C rainbow-like reflection on the body surface D free-living adult collected in wet soil E, F infected host, Spirobolus sp. nov. (Hsu and Chang, unpublished), harboring (E) three immature worms (arrow) and (F) an adult worm. Photographs courtesy of (D) Fang, Hua-Te and (F) Hung, Ming-Chin. Scale bars: 1 cm (E).
Eggs (N = 12) (Fig.
Living larvae (N = 10) (Fig.
Larvae treated with hot water (N = 2) (Fig.
Field-collected cysts (N = 5) (Fig.
Immature stages of Gordius chiashanus sp. nov. A, B free-living larva (A) treated with hot water and a living larva showing the depression in the anterior end of the pseudointestine (arrow) C, D eggs with the inner membrane examined using an (C) SEM and (D) compound microscope E egg strings F–H cysts in the paratenic host with (F) a unfolded larva and (G) a folded larva, showing (H) a single posterior spine (arrow) after treatment with a 5% KOH solution. Abbreviations: Ho, hooklet; PostS, postseptum; PreS, preseptum; Pro, proboscis; PsI, pseudointestine. Scale bars: 50 µm (A–D, F–H), 1 mm (E).
List of COI sequences obtained from GenBank for phylogenetic analyses in this study.
Accession number | Species/clade | Reference |
---|---|---|
Gordius/Acutogordius | ||
KM382317 | G. cf. robustus (Clade 8) |
|
KM382316 | ‘’ |
|
KM382315 | ‘’ |
|
KM382314 | ‘’ |
|
KM382313 | ‘’ |
|
KM382312 | ‘’ |
|
KM382311 | ‘’ |
|
KM382310 | G. terrestris |
|
KM382309 | ‘’ |
|
KM382308 | ‘’ |
|
KM382307 | ‘’ |
|
KM382306 | G. cf. robustus (Clade 6) |
|
KM382305 | ‘’ |
|
KM382304 | ‘’ |
|
KM382303 | ‘’ |
|
KM382302 | ‘’ |
|
KM382301 | ‘’ |
|
KM382300 | ‘’ |
|
KM382299 | ‘’ |
|
KM382297 | G. cf. robustus (Clade 5) |
|
KM382296 | ‘’ |
|
KM382295 | ‘’ |
|
KM382294 | G. cf. robustus (Clade 4) |
|
KM382293 | ‘’ |
|
KM382292 | ‘’ |
|
KM382291 | ‘’ |
|
KM382290 | ‘’ |
|
KM382289 | G. cf. robustus (Clade 3) |
|
KM382288 | ‘’ |
|
KM382287 | ‘’ |
|
KM382286 | ‘’ |
|
KM382285 | ‘’ |
|
KM382284 | ‘’ |
|
KM382283 | G. cf. robustus (Clade 2) |
|
KM382282 | ‘’ |
|
KM382281 | G. cf. robustus (Clade 1) |
|
KM382280 | ‘’ |
|
KM382279 | ‘’ |
|
KM382278 | ‘’ |
|
KM382277 | ‘’ |
|
KM382318 | G. attoni |
|
KM382319 | ‘’ |
|
KM382320 | G. balticus |
|
KM382321 | Gordius sp. N178 |
|
KM382322 | Gordius sp. N183 |
|
KM382323 | Gordius sp. N297B |
|
KM382324 | Gordius sp. N357 |
|
AB647235 | Gordius sp. KW-2011-A |
|
AB647237 | Gordius sp. KW-2011-B |
|
AB647241 | Gordius sp. KW-2011-D |
|
KY172751 |
Gordius sp. |
|
KY172750 | ‘’ |
|
KY172752 | ‘’ |
|
KY172759 | ‘’ |
|
KY172765 | ‘’ |
|
KY172770* | ‘’ |
|
KY172777 | ‘’ |
|
KY172749 | ‘’ |
|
KY172792 | ‘’ |
|
KY172789 | ‘’ |
|
KY172791 | ‘’ |
|
KY172799 | ‘’ |
|
KY172801 | ‘’ |
|
KY172802 | ‘’ |
|
KY172804 | ‘’ |
|
KY172753 | G. paranensis (Clade2) |
|
KY172754 | ‘’ |
|
KY172755 | ‘’ |
|
KY172756 | ‘’ |
|
KY172776 | ‘’ |
|
KY172782 | ‘’ |
|
KY172813 | ‘’ |
|
KY172811 | G. paranensis (Clade1) |
|
KY172812 | ‘’ |
|
KX591948 | Acutogordius taiwanensis |
|
KX591947 | ‘’ |
|
KX591946 | ‘’ |
|
KX591945 | ‘’ |
|
KX591944 | ‘’ |
|
KX591943 | ‘’ |
|
KX591942 | ‘’ |
|
KX591941 | ‘’ |
|
KX591940 | ‘’ |
|
KX591939 | ‘’ |
|
KX591938 | ‘’ |
|
KX591937 | ‘’ |
|
KX591936 | ‘’ |
|
KX591935 | ‘’ |
|
KX591934 | ‘’ |
|
KX591933 | ‘’ |
|
KX591932 | ‘’ |
|
KX591931 | ‘’ |
|
KX591930 | ‘’ |
|
KX591929 | ‘’ |
|
KX591928 | ‘’ |
|
KX591927 | ‘’ |
|
KX591926 | ‘’ |
|
KX591925 | ‘’ |
|
KX591924 | ‘’ |
|
KX591923 | ‘’ |
|
KX591922 | ‘’ |
|
MF983649 | Myanmar nematomorph | |
Out group | ||
HM044105 | Chordodes formosanus |
|
HM044124 | ‘’ |
|
KY172780 | Euchordodes nigromaculatus |
|
KY172803 | ‘’ |
|
KY172747 | Parachordodes diblastus |
|
KY172778 | ‘’ |
|
The partial COI sequences of the 18 free-living adults contained 15 haplotypes with 392 invariable sites, nine singletons, and 21 parsimoniously informative sites. The genetic distance among them was 0.0024 within the range of 0.0000–0.0510. The three living adults and six worms inside the hosts were considered conspecific with the 18 free-living adults because of their small genetic distances (0.0000–0.0719). The mean interspecific genetic distances between Gordius chiashanus sp. nov. and other Gordius species or clades were in the range of 0.2320–0.4242, and that between Gordius chiashanus sp. nov. and Acutogordius taiwanensis was 0.3648 (Table
Free-living adult worms frequently aggregate and mate on wet ground (Fig.
The 21 free-living Gordius adults and six juvenile worms from round-backed millipedes were judged as belonging to the same species in accordance with the results that they all were located in the same clade in the phylogenetic tree and had low genetic distances (Fig.
Intra- and interspecific mean COI genetic distances of Gordius/Acutogordius species or clades under K2P model.
Species/Clade | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Gordius chiashanus sp. nov. | 0.024 | |||||||||||||||||||||
2 | G. cf. robustus (Clade1) | 0.285 | 0.009 | ||||||||||||||||||||
3 | G. cf. robustus (Clade2) | 0.312 | 0.217 | 0.015 | |||||||||||||||||||
4 | G. cf. robustus (Clade3) | 0.293 | 0.297 | 0.275 | 0.007 | ||||||||||||||||||
5 | G. cf. robustus (Clade4) | 0.308 | 0.208 | 0.249 | 0.157 | 0.012 | |||||||||||||||||
6 | G. cf. robustus (Clade5) | 0.272 | 0.165 | 0.211 | 0.227 | 0.222 | 0.003 | ||||||||||||||||
7 | G. cf. robustus (Clade6) | 0.293 | 0.257 | 0.251 | 0.255 | 0.228 | 0.259 | 0.006 | |||||||||||||||
8 | G. terrestris | 0.232 | 0.209 | 0.265 | 0.250 | 0.230 | 0.222 | 0.238 | 0.020 | ||||||||||||||
9 | G. cf. robustus (Clade8) | 0.265 | 0.203 | 0.307 | 0.338 | 0.253 | 0.244 | 0.251 | 0.122 | 0.026 | |||||||||||||
10 | G. attoni | 0.277 | 0.229 | 0.288 | 0.337 | 0.274 | 0.238 | 0.289 | 0.231 | 0.249 | 0.010 | ||||||||||||
11 | G. balticus | 0.316 | 0.260 | 0.298 | 0.288 | 0.269 | 0.274 | 0.304 | 0.264 | 0.323 | 0.337 | – | |||||||||||
12 | Gordius sp. N178 | 0.352 | 0.260 | 0.313 | 0.370 | 0.289 | 0.340 | 0.330 | 0.256 | 0.290 | 0.271 | 0.323 | – | ||||||||||
13 | Gordius sp. N183 | 0.329 | 0.302 | 0.290 | 0.373 | 0.317 | 0.344 | 0.365 | 0.294 | 0.336 | 0.277 | 0.301 | 0.246 | – | |||||||||
14 | Gordius sp. N297B | 0.424 | 0.416 | 0.462 | 0.547 | 0.441 | 0.443 | 0.478 | 0.375 | 0.412 | 0.348 | 0.455 | 0.343 | 0.414 | – | ||||||||
15 | Gordius sp. N357 | 0.332 | 0.366 | 0.387 | 0.420 | 0.376 | 0.396 | 0.302 | 0.357 | 0.359 | 0.379 | 0.439 | 0.375 | 0.434 | 0.441 | – | |||||||
16 | Gordius sp. KW-2011-A | 0.384 | 0.325 | 0.327 | 0.453 | 0.371 | 0.336 | 0.345 | 0.347 | 0.348 | 0.331 | 0.376 | 0.332 | 0.376 | 0.372 | 0.424 | – | ||||||
17 | Gordius sp. KW-2011-B | 0.334 | 0.375 | 0.365 | 0.370 | 0.334 | 0.407 | 0.364 | 0.302 | 0.363 | 0.333 | 0.380 | 0.323 | 0.358 | 0.333 | 0.308 | 0.290 | – | |||||
18 | Gordius sp. KW-2011-D | 0.375 | 0.300 | 0.344 | 0.393 | 0.373 | 0.294 | 0.388 | 0.388 | 0.367 | 0.369 | 0.405 | 0.384 | 0.390 | 0.374 | 0.403 | 0.312 | 0.301 | – | ||||
19 | G. paranensis (Clade1) | 0.369 | 0.405 | 0.381 | 0.450 | 0.381 | 0.410 | 0.359 | 0.373 | 0.395 | 0.409 | 0.398 | 0.408 | 0.466 | 0.426 | 0.453 | 0.415 | 0.386 | 0.440 | 0.049 | |||
20 | G. paranensis (Clade2) | 0.337 | 0.348 | 0.391 | 0.436 | 0.384 | 0.372 | 0.368 | 0.333 | 0.368 | 0.345 | 0.339 | 0.334 | 0.385 | 0.324 | 0.404 | 0.357 | 0.327 | 0.344 | 0.377 | 0.010 | ||
21 |
Gordius sp. |
0.335 | 0.283 | 0.293 | 0.436 | 0.355 | 0.311 | 0.366 | 0.287 | 0.337 | 0.347 | 0.358 | 0.254 | 0.308 | 0.343 | 0.353 | 0.304 | 0.335 | 0.321 | 0.354 | 0.337 | 0.012 | |
22 | Acutogordius taiwanensis | 0.365 | 0.343 | 0.327 | 0.401 | 0.386 | 0.368 | 0.345 | 0.322 | 0.375 | 0.304 | 0.336 | 0.270 | 0.210 | 0.462 | 0.469 | 0.432 | 0.376 | 0.366 | 0.435 | 0.389 | 0.311 | 0.002 |
The concentration of bristles and spines on the male tail lobes has been previously described in species from the Palaearctic (
Although the distribution pattern of the bristles is similar to that of G. helveticus, G chiashanus sp. nov. is morphologically distinct because of the presence of stout bristles on the mid-body, a vertical white stripe on the anterior ventral side, and areoles on the inside wall of the cloacal opening. The vertical white stripe on the anterior ventral side can be easily observed by the naked eye, but it has rarely been mentioned thus far. The presence of a white stripe was previously reported in the terrestrial hairworm, G. terrestris (
Gordius chiashanus sp. nov. and the two previously described species, namely A. taiwanensis
Morphology of Gordius chiashanus sp. nov. With approximately 90 valid species, Gordius is the second most diverse genus of the phylum Nematomorpha (
Adult and larval size. The body length of Gordius is variable and can be longer than 2 m (
Phylogenetic relationship of Gordius and Acutogordius. Molecular comparisons have been rarely conducted in the 19 nematomorph genera (
Definitive host and route of transmission. The millipede has been known to be the host of horsehair worms, including the genera Gordius and Gordionus (
Host and host manipulation of horsehair worms. The host and biological characteristics of Gordius chiashanus sp. nov. suggest an atypical life history. In general, freshwater horsehair worms (gordiids) develop in terrestrial definitive hosts and reproduce in aquatic environments (
In this study, the female adult oviposited in the water. The cysts found in the aquatic paratenic hosts and the eggs developing in water also suggest the life cycle of Gordius chiashanus sp. nov. could occur in water and on land. However, the current evidence did not exclude the oviposition in the terrestrial environment because no terrestrial paratenic host was examined for cysts. In addition, the double membraned egg (
We deeply appreciate the assistance provided by Hua-Te Fang, Po-Yen Chen, Yu-Hsuan Tsai, Ta-Chih Chen, and Yu-Wei Li during sample collection, Wei-Chun Chien during SEM examination, and Masato Nitta, Rui Ueda, Takuya Sato, and Scotty Yang during DNA sequencing. We specially thank Ming-Chin Hung for providing host information. This manuscript was edited by Wallace Academic Editing.
Video S1
Data type: multimedia
Explanation note: Free-living adult of Gordius chiashanus sp. nov. moving on the ground at night, with a rainbow-like reflection on the body surface.
Fasta 2
Data type: molecular data
Explanation note: COI sequences adopted in the phylogenetic analysis, including for Gordius/Acutogordius spp. with Chordodes formosanus, Euchordodes nigromaculatus, and Parachordodes diblastus as out groups.