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. 2022 Mar 16;10:e13010. doi: 10.7717/peerj.13010

Onyx disparamphis sp. n. (Nematoda, Desmodorida) from South Korea with a taxonomic review of the genus

Alexei V Tchesunov 1,✉, Raehyuk Jeong 2, Wonchoel Lee 3
Editor: Natalia Zhukova
PMCID: PMC8934044  PMID: 35313521

Abstract

A new free-living marine nematode Onyx disparamphis sp. n. (Nematoda, Desmodorida) is described from sandy littoral of Jeju Island, South Korea. The new species differs from all other Onyx species by the unusual amphideal fovea morphology in males (elongated loop). O. disparamphis relates to O. balochinensis, and O. brevispiculatum by having simple non-double terminal pharyngeal bulb and relatively small and straight, non-sigmoid supplementary organs, but differs from them by smaller body length, shorter cephalic setae, smaller terminal pharyngeal bulb, smaller spicules, number of supplementary organs and tail shape expressed as ratio tail length/anal diameter. The genus Onyx is revised with updated genus diagnosis, and an annotated list of 23 valid species is presented. Onyx ferox is considered species inquirenda because the species is known only from a sole immature female specimen, while within Onyx, the males provide the most important distinguishing characters such as enlarged and complicated amphids, supplementary organs and copulatory spicules. For species identification, a pictorial key consisting of illustrations of simplified icons of male heads and posterior body sections, as well as a table of the most important morphometric and numerical characters are provided. Geographical distribution and habitat specifity of Onyx species is analysed briefly.

Keywords: Desmodoridae, Free-living marine nematodes, Jeju Island, Pictorial key, Taxonomy, Onyx, New species

Introduction

As part of the study of meiofauna and nematodes on the intertidal sandy littoral of the Jeju Island (South Korea), we have found a number of new nematode species which are partly already published (Jeong, Tchesunov & Lee, 2019; Jeong, Tchesunov & Lee, 2020; Tchesunov, Jeong & Lee, 2020; Tchesunov, Jeong & Lee, 2021). Here, we report on a new Onyx species common on this beach.

Nematode genus Onyx has been established by N.A. Cobb (1891) for a species found by him in so called Amphioxus-sand in the Bay of Naples, Italy. Cobb marked single axial spear attached to the dorsal side of the pharynx as the prominent trait of Onyx perfectus, which provided a ground to consider an evident kinship with the genus Dorylaimus. This relationship was later recognized as superficial, and Onyx was taken as a relative of Metachromadora (Filipjev, 1918: 214, at that time, Chromadoridae, Spilipherini) and then within Desmodorinae (Filipjev, 1934). Thereafter, Onyx has a stable position in the nematode system as a genus of the order Desmodorida, family Desmodoridae and subfamily Spiriniinae.

Onyx is a globally distributed, well-defined genus within the the family Desmodoridae which is mainly found in shallow coastal sediments. Species of Onyx are usually well recognizable owing to their bold and distinct structural features. Consequently, there are limited nomenclatural problems or bynonyms within the genus. However, the number of species grows, especially by the exploration of tropical meiofauna, that leads to increasing complexity in species identification. Coupled with new species description, several reviews of the genus Onyx were suggested (Blome & Riemann, 1994; Nasira, Rehmat & Shahina, 2011; Armenteros, Ruiz-Abierno & Decraemer, 2014; Huang & Wang, 2015). Increase in number of species requires periodical taxonomic revisions with proper adjustment of species composition and construction of improved keys for species identification.

Here, we propose description of a new species together with revised species list and pictorial key for species identification.

Materials & Methods

The nematodes were collected and studied in frame of a project on exploration interstitial fauna of sandy beaches of South Korea. The site of sampling is a large intertidal sandy beach Shinyang Seopjikoji at the south-eastern point of Jeju Island (Fig. 1).

Figure 1. Type locality of Onyx disparamphis sp. n.

Figure 1

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The quantitative sediment samples were initially fixed by neutralized 5% formol on filtered sea water. Meiofauna including nematodes was separated from sediment using method of centrifugation with Ludox (Burgess, 2001), then postfixed with 70% ethanol stained with Rose Bengal. Nematode specimens were picked up under a stereomicroscope and placed in Syracuse glass with mixture of glycerine, ethanol and distilled water at a ratio of 1:29:70. After slow evaporation of ethanol and water during two days at 40° in an oven the nematodes become completely dehydrated as described by Seinhorst (1959). Nematode specimens were mounted in permanent glycerin slides within bee-wax-paraffin glass and with glass beads as separators. Specimens were studied, measured, pictured and drawn in the optical microscope Leica DM 5000 equipped with IC measure v.2.0.0.161 software and digital camera Leica DFC 425C. For scanning electron microscopy (SEM), specimens fixed in formalin in filtered sea water were then dehydrated in a graded series of ethanol-acetone solutions. Specimens were critical point-dried with carbon dioxide. Dried specimens were mounted on stubs, coated with gold-palladium mixture, and examined with a CAMScan S-2.

Type specimens are deposited in National Institute of Biological Resources (South Korea).

Nomenclatural acts

The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: 2FA0F335-DF23-4824-A3DC-A04DD46289BD. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central SCIE and CLOCKSS.

Results and Discussion

Review of the genus Onyx

Order Desmodorida Chitwood, 1936
Family Desmodoridae Filipjev, 1922
Subfamily Spiriniinae Gerlach & Murphy, 1965
Genus OnyxCobb, 1891
Diagnosis (updated after Tchesunov, 2014)
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Desmodoridae, Spiriniinae. Cylindrical body with broad rounded cephalic region and conical tail. Cuticle thin, fine but distinctly annulated, without lateral differentiation. Amphideal fovea spirally coiled in one to several turns or modified; the fovea often shifted to apical surface of the head. Buccal cavity with long spear-like dorsal tooth directed anteriorly. Terminal pharyngeal bulb mostly elongate, may be double with lens-like thickened internal cuticular lining or the lining not thickened. Numerous midventral precloacal supplementary organs tubular and in most species S-shaped. Tail conical.

Type species, Onyx perfectus Cobb, 1891. Altogether 23 valid species, all marine.

Annotated species list (names of valid species in bold)

Description of new species of Onyx

Onyx disparamphis Tchesunov, Jeong & Lee sp. n.
Figs. 2–6, Table 1
urn:lsid:zoobank.org:act:C403A850-22EB-43A2-9A51-E2CCCB36364A
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Figure 2. Onyx disparamphis sp. n., entire: Male (holotype) (A); Female (paratype) (B).

Scale bars 100 µm.

Figure 2

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Figure 6. Onyx disparamphis sp. n., details in SEM-micrographs: (A) male head, long amphideal fovea; (B) male head, subapical view; (C) female head, subapical view; (D) male posterior body; (E) male supplementary organs (anterior body end to the left).

Figure 6

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Scale bars: A, B: 10 µm; C, E: 3 µm; D: 30 µm.

Table 1. Morphometrics of Onyx disparamphis sp. n. type specimens.

Character Holotype male Males (holotype and paratypes together) Female paratypes
n min–max mean SD CV n min–max mean SD CV
Body length, µm 840 18 7503–1014 873 60.5 6.94 13 695–889 800 55.1 6.89
a 33.1 17 28.8–40.5 34.0 3.26 9.58 13 20.0–27.8 22.5 2.15 9.54
b 5.46 17 4.66–6.26 5.55 0.37 6.67 13 4.59–5.40 4.98 0.26 5.22
c 13.8 17 9.35–13.8 11.2 1.26 11.3 12 9.71–14.2 11.4 1.16 10.2
c’ 3.54 13 2.48–4.34 3.47 0.54 15.6 12 2.48–4.11 3.36 0.39 11.6
V, % – – – – – – 12 46.4–53.5 50.6 2.24 4.43
Body diameter at the level of the subcephalic setae, µm 24 12 20.0—25.9 23.9 1.83 7.66 10 22.0–34.0 27.7 3.67 13.3
Body diameter at the level of the nerve ring, µm 26 18 23.4–28.9 26.0 1.31 5.04 13 27.6–31.4 29.4 1.17 3.98
Body diameter at the level of the cardia, µm 26 18 24.1–30.0 26.1 1.37 5.24 13 29.0–37.0 32.5 2.38 7.33
Body diameter at the level of the midbody, µm 25 17 23.9–28.0 25.7 1.05 4.09 13 32.0–40.0 35.6 1.85 5.19
Body diameter at the level of the cloaca/anus, µm 23 13 21.0–25.6 23.3 1.33 5.72 13 19.0–25.0 21.4 1.59 7.45
Cephalic setae length, µm 12 16 9.30–14.2 11.4 1.22 10.7 11 6.50–13.0 10.2 1.98 19.3
Subcephalic setae length, µm 13 12 8.40–13.4 11.8 1.37 11.6 6 9.60-12.5 10.5 1.10 10.5
Amphid width anteriorly, µm 6 5 5.30–7.50 6.54 0.88 13.5 5 6.80–8.00 7.34 0.61 8.31
Amphid furrow length, µm 73 13 340–100 73.0 16.6 22.8 – – – – –
Stoma total length, µm 53 16 42.0–66.0 49.8 6.52 13.1 12 43.6–62.0 53.0 5.51 10.4
Dorsal tooth length ventrally, µm 9 14 26.8–39.6 34.4 3.48 10.1 11 33.0–40.3 29.4 12.2 41.7
Dorsal tooth length dorsally, µm 40 14 6.80–9.80 8.30 0.97 11.7 12 5.00–19.9 9.67 3.96 41.0
Terminal bulb length, µm 41 17 38.6–50.0 44.5 3.19 7.17 13 49.2–62.0 55.4 4.15 7.50
Terminal bulb width, µm 18 18 15.5–19.9 17.1 1.12 6.53 13 17.8–27.0 22.9 2.42 10.6
Number of precloacal supplements 18 13 14–19 16.9 1.52 9.02 – – – – –
Spicules, length along the arc, µm 35 16 33.2–40.0 36.3 1.91 5.26 – – – – –
Spicules, length along the chord, µm 26 16 23.4–30.4 26.7 1.99 7.45 – – – – –
Gubernaculum length, µm 16 16 12.3–19.5 15.5 1.97 12.7 – – – – –
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Notes.

n, number of individuals; min–max, range, SD, standard deviation; CV, coefficient of variation (SD divided by mean, in %%)

Etymology

The species name reflects strong sexual dimorphism in amphideal fovea outline.

Figure 5. Onyx disparamphis, optical micrographs: Male paratype, entire (A). Head of a juvenile specimen, optical section (B). Male paratype tail (C). Male paratype copulatory apparatus and posterior supplementary organs (D).

Figure 5

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Scale bars: A –100 µm; B–D –1.

Material examined

Holotype male, 17 paratype males and 13 paratype females are deposited in the National Institute of Biological Resources (South Korea). Inventory numbers of the holotype male is U1-5 r2 sl8, paratype males 1 and 2 are M1-5 r1 sl12, paratype male 3 and paratype female 1 –slide M1-5 r1 sl14, paratype females 2 and 3 –slide M1-5 r2 sl6, paratype males 4, 5 and 6 –slide U0-1 r2 sl15, paratype females 4 and 5 –slide U15-20 r1 sl3.

Type locality

Intertidal zone at coast of Jeju Island, South Korea (33°26′05″N, 126°55′15″E), sandy beach, June 19, 2019.

Description

Males. Body cylindrical, anterior end rounded truncated, tail conical (Figs. 1A, 4A). Cuticle thin, fine but distinctly cross annulated, without a lateral differentiation. Numbers of cuticular annules within 10 µm varies along the body: 14 annules within 10 µm at the level of the long amphideal branch and 18 less distinct annules within 10 µm at the midbody.

Figure 4. Onyx disparamphis sp. n., details of the male holotype: Anterior body (A); Posterior body (B).

Figure 4

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Scale bars 20 µm.

Apical region of the cephalic region not annulated but finely longitudinally striated, with sharp border between longitudinal striation and annulation (Figs. 6B, 6C). Inner labial sensilla not evident. Outer labial sensilla as six minute papillae (1–1.5 µm). Four long cephalic setae situated apically and directed anteriorly. There first, anterior crown of eight subcephalic setae located just posterior to the cephalic setae at the level of the anterior margin of cross annulation of the cuticle. The second, posterior, less regular crown of eight subcephalic setae located slightly anterior to the middle point of the long amphideal branch. The subcephalic setae of both crowns and several irregular singular setae in the preneural body region are about equal in length and breadth to one another and to cephalic setae. Other shorter somatic setae are dispersed sparsely along the body. There are cuticular pores distributed along the body; which look like a minute hole in the centre of a smooth circular spot on the cuticle (Fig. 3A, arrow).

Figure 3. Onyx disparamphis sp. n., anterior ends. Male holotype, surface view (A). Male holotype, optical section (sensilla not depicted) (B). Female paratype (C).

Figure 3

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Scale bars 20 µm. Arrow indicates a circular pore.

Amphids shifted onto the apical area of the cephalic region. Anterior end of the amphideal fovea is located on apical surface close to the mouth opening; the fovea turns dorsally and runs on into the long dorsal arm of the fovea extended far hindward as elongated loop with tight but distinct ridge-like interspace between two arms (Figs. 3A, 3C; 6A–6C).

Somatic cuticle not widened around the mouth. Cheilostoma shaped as a truncate cone with longitudinal rugosity. Long and narrow pharyngostoma armed with a long dorsal tooth provided with a conical pointed cuticular arrowhead (corona). The tooth is adherent dorsally to the pharynx tissue at two thirds of its length. Pharyngostoma is surrounded by inflated pharyngeal tissue with fine transversal striation. Middle part of the pharynx slender; posterior part of the pharynx is formed as an elongate terminal bulb with muscular cross striation. Internal cuticular lining of the bulb with muscular cross striation not thickened and seemingly not modified. Midgut slender, filled with orange pigment inclusions.

No renette found.

Testis singular anterior, outstretched, situated to the left of the intestine in all the male specimens. Spicules paired and equal, short, arcuate, proximally cephalated and distally pointed. Gubernaculum S-shaped and oriented perpendicularly to the longitudinal body axis. Series of 14–19 equal midventral precloacal supplementary organs. Supplements consist of three constituents, (1) surface cuticular pit with cuticularized walls, (2) core within the pit, head of the core bears a longitudinal ridge with a papilla, (3) short internal straight cuticular tube extending from the pit obliquely inward (Figs. 4B, 6D–6E).

Tail conical, with caudal glands and a terminal spinneret. Caudal gland cell bodies hardly discernible, visibility limited within tail, but may have seemingly pushed out to preanal region in some specimens.

Females. Amphideal fovea spirally coiled in three turns and situated entirely on the cephalic apex close to the mouth opening (Figs. 3C, 6C).

Ovaries paired, antidromously reflected, both situated to the left of the intestine in all female specimens studied (Fig. 1B).

Diagnosis

Body length 695–1014 µm, index a 20–40.5, index c’ 2.5–4.34. Cephalic setae 6.5–14.2 µm long. Two subsequent crowns of eight subcephalic setae similar in length to the cephalic ones. Amphideal fovea shows strong sexual dimorphism: in females, the amphideal fovea spirally coiled in three turns and located entirely on the head apex, while in males, the fovea turns dorsally from the aperture on the apex, then extended hindward as elongated loop. Dorsal tooth 27–40 µm along the ventral side. Terminal bulb of the pharynx elongated, 40–60 µm long, with faint internal lining. Spicules arcuate, 33–40 µm long. Midventral precloacal supplementary organs 14–19 in number, consist of flat cap and internal short and almost straight cuticular tubes. Tail conical, c’ 2.4–4.3.

Relationships

Onyx disparamphis sp. n. differs immediately from all other Onyx species by the peculiarly very long loop of the amphideal fovea of males. O. disparamphis shares simple non-double terminal pharyngeal bulb with thirteen other Onyx species (Table 2), among them O. balochinensis, and O. brevispiculatum may show some resemblance in shape of supplementary organs, relatively small and straight, non-sigmoid. O. disparamphis differs from O. balochinensis by smaller body length (690–1014 versus 1240–1640 µm), smaller cephalic setae (6.5–15 versus 17–22 µm), smaller terminal pharyngeal bulb (38–62 versus 84–105 µm in length) and smaller spicules (33–40 versus 45–50 µm). O. disparamphis differs from O. brevispiculatum by also smaller body (695–1014 versus 1800–3300 µm), twice the lower number of supplementary organs (14–19 versus 39) and relatively longer tail (c’ 2.4–4.4 versus 1.2).

Table 2. Characters of Onyx species (males).

Species Characters
Body length a Cephalic setae length Dorsal tooth length Terminal pharyngea l bulb, length & shape, internal lining Number of supplements Spicule length c’
adenophorus 1154 41 10 23 50, elongate, double, lining cuticularized 18, sigmoid 29 2.1
balochiensis 1240–1640 39–52 17–19 32–36 84–100, inconspicuously double, lining faint 15–23, tubular 45–50 2.3–3.2
blomei 697–756 25–28 6–6.5 26–29 50, elongate, lining faint 7–8 tubular, slightly S-shaped 34–35 3.5–3.7
brevispiculatum 1800 22 ? ? no true bulb but slight swelling, lining faint 39 crochet-shaped 117 1.2 calc
cangioensis 679–759 20–23 5 31–36 29 calc, oval, lining faint 14–16, tubular 45–49 2.4–3
cannoni 1032 44 8 22 46 calc, elongate; lining faint 15, tubular 28 ∼2 calc
cephalispiculus 1204–1284 20–28 12–15 ∼40 calc 70 calc, elongate, double, lining cuticularized 18–24, S-shaped 65–75 2.4 calc
cobbi 1334–1544 31–40 21–22 39–43 80 calc, elongate, double, lining cuticularized 15–16, tubular 42-46 3–3.7
dimorphus 1080 21 15–20 50 66–85, elongate, lining faint 10, S-shaped 45 2.6
disparamphis 750–1014 28–41 9.3–15 26–40 38–50, elongate, lining faint 14–19, straight tubular 33–40 2.5–4.4
litorale 1100–1360 28 & 20 15 35 64, elongate, lining faint 15–20, sigmoid 190–200 3.4 calc
macramphis 813 37 8 29 42, elongate, lining faint 14, tubular 27 2.9
mangrovi 523–591 12–15 3 & 3 30–36 70 calc, lining faint 17–23, tubular sigmoid 36–40 1,1–1,4
minor 675–806 35–41 7 21–22 33–40, elongate, double, lining lens-like cuticularized 12, tubular S-shaped 22–25 3.3–3.5
monstrosum 1865–2059 43–49 13 ? 81, double, lining lens-like cuticularized 19–21, sigmoid 55–60 3
orientalis 974–1003 39–44 15–17 24–27 76 calc, double, lining lens-like cuticularized 17–18, tubular 38–40 2.5–2.8
paradimorphus 1003–1196 25-31 18 44 70 calc, double, lining lens-like cuticularized 15, sigmoid tubular 41–44 4.2–4.3
perfectus 1740–2160 37–39 22–28 53–56 88 calc, elongate, lining faint 13–22, sigmoid 45–70 2
potteri 1112 40 14 ? 55 calc, elongate, internal lining faint 10, slightly sigmoid 50 3 calc
rizhaoensis 1213–1330 44–45 10 20–22 55 calc, elongate, double, lining lens-like sclerotized 12, sigmoid 30 2.6–2.8
rugatus 1300 32–33 19 40 calc 90, double, lining lens-like cuticularized 22, complicated papillae 42 2.7
sagittarius 1070 28 5 30 60, double, lining faint 24, slightly sigmoid 35 2
septempapillatus 1320 40 20 21 75, double, lining cuticularized 7, small and nearly straight 37 3
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Ecological remarks

Onyx disparamphis is a common, but not very numerous species on the Shinyang beach, being the 12th most abundant and comprising 1.6% of total nematode abundance of the beach. O. disparamphis is distributed across the whole intertidal sandy beach from lower to upper horizon, with some increase in numbers at middle and upper horizons. No obvious confinedness to a certain layer in vertical sediment column is observed, evidently because of uniformity of conditions (granulometry) within a sediment depth 0–20 cm.

Microscopic examination of gut content does not reveal any evident particles or identifiable remnants. The intestine of the individuals studied either appear empty or with spherical drops. The long and strong dorsal tooth may protrude from the mouth as it is shown for Onyx sagittarius by Gerlach (1950, Abb. 5c). We suppose that Onyx disparamphis and its congeners could pierce covers of some food items (e.g., protists) and suck out the liquid matter by muscular bulb pumping.

Pictorial key for identification Onyx species

The present pictorial key for identification of 23 valid species of Onyx is constructed based on principles of Platt (1984), who first introduced such keys in marine nematology. The key consists of two components, (1) a set of species icons or pictorial key (Figs. 7–8), and (2) a table of the most important morphometric and numerical characteristics (Table 2). Most valid species are known on both males and females, and only two species, O. monstrosum and O. orientalis are described based only on males. Only males are used for pictures since they provide more distinctly perceiving features (such as amphids) on the head and much more features (such as copulatory and supplementary organs) on the posterior body. The table 2 includes characteristics of only males, because females are not known for two species and data on females are often less complete in comparison with males in other descriptions based on two sexes.

Figure 7. Pictorial key to Onyx species, male heads. Beginning.

Figure 7

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Figure 8. Pictorial key to Onyx species, male heads. Continuation.

Figure 8

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On Figs. 7–8, the heads are arranged in such an order that species having the largest and most conspicuous amphideal fovea are located at the top of the key; by scanning the icons from top to bottom, the amphids and head setae become gradually smaller and shorter.

Spatial distribution of Onyx species

Like most other marine nematode superspecies taxa, the genus Onyx shows a worldwide distribution (Fig. 9); however, most species are confined with warm waters, and none occurs in Arctic and Antarctic (with possible exception O. ferox sp. inq. in Subantarctic). Nine species are recorded in tropical areas (balochiensis, blomei, cangioensis, cobbi, dimorphus, mangrove, orientalis, paradimorphus, perfectus); eight species in subtropical regions (adenophorus, brevispiculatum, cannoni, cephalispiculus, macramphis, perfectus, potteri, sagittarius), nine species in temperate regions (disparamphis, littorale, minor, monstrosum, perfectus, rizhaoensis, rugatus, sagittarius, septempapillatus). Surprisingly, there were no Onyx species recorded along the east coasts of the Americas, but this is likely due to insufficient information on meiofauna in this specific region. A cluster of six co-occuring species within a limited area was found in the CanGio mangrove habitat (South Vietnam) in silty sediment at a depth 0.5 m.

Figure 9. Geographical distribution of Onyx species.

Figure 9

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Species are designated with three first letters of the names. Type localities are in bold.

All the Onyx species are confined with coastal shallows, from intertidal zone to upper sublittoral of several tens of meters depth; no species are recorded from the deep sea. The majority of species inhabits coarse sands (16 of 24 species), often on high energy beaches. The remaining eight species were found on silts, most of them (six) in mangrove milieu.

Conclusions

The sandy intertidal at Shinyang, Jeju Island, is distinguished by its high nematode diversity. We have recorded over 90 nematode species belonging to 73 genera, 31 families and eight orders. To date, only ten species are identified up to species level and five of them having been proved new for science are published. The next taxa to be treated are the most diverse families Xyalidae and then Chromadoridae composing respectively 17% and 14% of all species revealed there.

Supplemental Information

Supplemental Information 1. Raw morphometric data of Onyx disparamphis sp. n.

The table of raw data contains all morphometric data for all type specimens of Onyx disparamphis sp. n. The data allow distinguish Onyx disparamphis fron all other Onyx species.

Left column presents dimensions, measurement and characters which are used normally for species discriminations. Uppermost line presents type specimens in slides.

Males and females are given on different sheets. Meanings of characters are not abbreviated and presented as is in the left column.

Statistical parameters in the right columns: n –number of specimens measured; min –minimal variable; max –maximal variable, mean –mean value, SD –standard deviation, CV –coefficient of variation (standard deviation divided by mean value, in %%).

Some variables are missing because of impossibility of measuring (damaged specimen, inconvenient location in slide) and replaced by “x”.

Click here for additional data file. (24.1KB, xlsx)
DOI: 10.7717/peerj.13010/supp-1

Acknowledgments

The authors thank Dr. Vadim Mokievsky (P.P. Shirsov Institute of Oceanology, Moscow) and Mrs. Maria Fedyaeva (Moscow State University) for their help in the field work sampling in June 2019. We appreciate the reviewers for their valuable remarks.

Abbreviations

a

body length divided by body diameter at midbody

b

body length divided by pharynx length

c

body length divided by tail length

c’

tail length divided by anal body diameter

calc

calculated or measured from published measurements and/or figures

V

distance from anterior end to vulva divided by entire body length, in %%

Funding Statement

This work was supported by a grant NIBR202102108 from the National Institute of Biological Sciences (NIBR) funded by the Ministry of Environment (MOE) of the Republic of Korea. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Additional Information and Declarations

Competing Interests

The authors declare that there are no competing interests.

Author Contributions

Alexei V. Tchesunov, Raehyuk Jeong and Wonchoel Lee conceived and designed the experiments, performed the experiments, analyzed the data, prepared figures and/or tables, authored or reviewed drafts of the paper, and approved the final draft.

Data Deposition

The following information was supplied regarding data availability:

The raw data are available as a Supplemental File.

New Species Registration

The following information was supplied regarding the registration of a newly described species:

Publication LSID: urn:lsid:zoobank.org:pub:A76B35DE-E24C-4EA9-9CB2-8DE1A95D10AB

Onyx disparamphis LSID: urn:lsid:zoobank.org:act:FAF768CE-5F30-40F2-896A-2670FA2AE35E.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplemental Information 1. Raw morphometric data of Onyx disparamphis sp. n.

The table of raw data contains all morphometric data for all type specimens of Onyx disparamphis sp. n. The data allow distinguish Onyx disparamphis fron all other Onyx species.

Left column presents dimensions, measurement and characters which are used normally for species discriminations. Uppermost line presents type specimens in slides.

Males and females are given on different sheets. Meanings of characters are not abbreviated and presented as is in the left column.

Statistical parameters in the right columns: n –number of specimens measured; min –minimal variable; max –maximal variable, mean –mean value, SD –standard deviation, CV –coefficient of variation (standard deviation divided by mean value, in %%).

Some variables are missing because of impossibility of measuring (damaged specimen, inconvenient location in slide) and replaced by “x”.

Click here for additional data file. (24.1KB, xlsx)
DOI: 10.7717/peerj.13010/supp-1

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