Research Article |
Corresponding author: Piotr Gąsiorek ( piotr.lukas.gasiorek@gmail.com ) Academic editor: Pavel Stoev
© 2020 Katarzyna Vončina, Reinhardt M. Kristensen, Piotr Gąsiorek.
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:
Vončina K, Kristensen RM, Gąsiorek P (2020) Pseudechiniscus in Japan: re-description of Pseudechiniscus asper Abe et al., 1998 and description of Pseudechiniscus shintai sp. nov. Zoosystematics and Evolution 96(2): 527-536. https://doi.org/10.3897/zse.96.53324
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The classification and identification of species within the genus Pseudechiniscus Thulin, 1911 has been considered almost a Sisyphean work due to an extremely high homogeneity of its members. Only recently have several contributions made progress in the taxonomy feasible through their detailed analyses of morphology and, crucially, by the re-description of the ancient, nominal species P. suillus (Ehrenberg, 1853). Herein, we focus on the Japanese representatives of this genus: P. asper, a rare species originally described from Hokkaido, and a new species P. shintai. Both taxa belong to the widespread suillus-facettalis complex. Detailed descriptions entailing DNA barcoding of four markers and illustrations of the ventral pillar patterns are indispensable for an accurate delineation of species within this genus.
biodiversity, Echiniscidae, Heterotardigrada, morphology, sculpturing
Tardigrades are poorly known micrometazoans famous for their ability to enter cryptobiosis (
Recent advances in the taxonomy of one of the echiniscid genera, Pseudechiniscus Thulin, 1911, are a good illustration of the progress currently being made in the classification of tardigrades. Firstly,
In this contribution, we concentrate on the Japanese Pseudechiniscus species. Pseudechiniscus asper Abe et al., 1998 is re-described and P. shintai sp. nov. is described, based on specimens from Aomori Prefecture (Northern Honshu). A brief review of Japanese Pseudechiniscus records is provided, concluding that they should be treated as unreliable and require formal confirmation through a new, large-scale sampling effort undertaken throughout Japan. Such a conclusion is in line with new discoveries of species complexes in numerous tardigrade genera (e.g.
Specimens belonging to two species of the genus Pseudechiniscus were extracted from four moss samples (JP.012–5) collected from trees in Asamushi, Northern Honshu, Japan (ca. 40°54'03.6"N, 140°51'58"E, 30 m a.s.l.; R.M. Kristensen leg. on 24 July 2019). Samples were processed according to the protocol developed by
Permanent microscope slides were made using Hoyer’s medium and examined using an Olympus BX53 PCM associated with an Olympus DP74 digital camera. All figures were assembled in Corel Photo-Paint X7. All measurements are given in micrometres (μm) and were performed under PCM. Structures were measured only when not broken, deformed or twisted and their orientations were suitable. Body length was measured from the anterior to the posterior end of the body, excluding the hind legs. The sp ratio is the ratio of the length of a given structure to the length of the scapular plate expressed as a percentage (
DNA was extracted from individual animals following a Chelex 100 resin (Bio-Rad) extraction method (
Primers and references for specific protocols for amplification of the four DNA fragments sequenced in the study.
DNA fragment | Primer name | Primer direction | Primer sequence (5’-3’) | Primer source | PCR programme* |
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18S rRNA | 18S_Tar_Ff1 | forward | AGGCGAAACCGCGAATGGCTC |
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18S_Tar_Rr2 | reverse | CTGATCGCCTTCGAACCTCTAACTTTCG |
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28S rRNA | 28S_Eutar_F | forward | ACCCGCTGAACTTAAGCATAT |
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28SR0990 | reverse | CCTTGGTCCGTGTTTCAAGAC |
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ITS-1 | ITS1_Echi_F | forward | CCGTCGCTACTACCGATTGG |
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ITS1_Echi_R | reverse | GTTCAGAAAACCCTGCAATTCACG | |||
COI | bcdF01 | forward | CATTTTCHACTAAYCATAARGATATTGG |
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bcdR04 | reverse | TATAAACYTCDGGATGNCCAAAAAA |
Phylum: Tardigrada Doyère, 1840
Class: Heterotardigrada Marcus, 1927
Order: Echiniscoidea Richters, 1926
Family: Echiniscidae Thulin, 1928
Genus: Pseudechiniscus Thulin, 1911
ca. 42°46'N, 141°24'E, 250 m a.s.l.; vicinity of the Lake Shikotsu (Chitose, South-western Hokkaido, Japan); foliose lichen Phaeophyscia imbricata (Physciaceae) on the trunk of a maple (Acer japonicum). Collector: Kazuo Utsugi. Holotype: adult male on the slide NSMT-Tg 44 deposited in the National Museum of Nature and Science in Tokyo.
Additional material. Four females on the slides JP.012.01, JP.013.01–2, JP.014.01 and a male on the slide JP.012.04. Hologenophores: JP.012.01, 4, JP.013.02.
From Latin asper = rough, referring to the irregular surface of dorsal plates. Adjective in the nominative singular.
Mature females (i.e. from the third instar onwards; measurements in Table
Habitus of Pseudechiniscus asper (PCM): A, B – females; C – male hologenophore. Insert shows claws III. Arrowheads indicate thickenings at the lateral positions C and D. List of abbreviations: c – caudal plate, cA – cirrus A, ce – cirrus externus, ci – cirrus internus, cp – cephalic plate, m1–3 – median plates, ps – pseudosegmental plate IV’, sI–II – paired segmental plates, sc – scapular plate. Scale bars: in μm.
Measurements [in µm] of selected morphological structures of mature females of Pseudechiniscus asper mounted in Hoyer’s medium (N – number of specimens/structures measured, RANGE refers to the smallest and the largest structure amongst all measured specimens; SD – standard deviation).
CHARACTER | N | RANGE | MEAN | SD | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
µm | sp | µm | sp | µm | sp | ||||||
Body length | 2 | 178 | – | 203 | 712 | – | 810 | 191 | 761 | 18 | 70 |
Scapular plate length | 2 | 25.0 | – | 25.1 | – | 25.1 | – | 0.1 | – | ||
Head appendages lengths | |||||||||||
Cirrus internus | 3 | 9.2 | – | 11.4 | 42.0 | – | 45.4 | 10.4 | 43.7 | 1.1 | 2.4 |
Cephalic papilla | 3 | 3.5 | – | 4.7 | 13.9 | – | 18.8 | 4.1 | 16.4 | 0.6 | 3.4 |
Cirrus externus | 3 | 14.8 | – | 19.4 | 59.2 | – | 77.3 | 16.6 | 68.2 | 2.5 | 12.8 |
Clava | 3 | 4.3 | – | 5.9 | 17.2 | – | 20.3 | 5.1 | 18.8 | 0.8 | 2.2 |
Cirrus A | 3 | 24.1 | – | 30.8 | 96.4 | – | 122.7 | 27.3 | 109.6 | 3.4 | 18.6 |
Cirrus A/Body length ratio | 2 | 14% | – | 15% | – | 14% | – | 1% | – | ||
Papilla on leg IV length | 4 | 3.0 | – | 3.6 | 12.0 | – | 13.9 | 3.4 | 13.0 | 0.3 | 1.4 |
Claw 1 heights | |||||||||||
Branch | 4 | 8.8 | – | 10.7 | 40.2 | – | 40.4 | 9.9 | 40.3 | 0.8 | 0.1 |
Spur | 4 | 1.2 | – | 1.8 | 4.8 | – | 6.4 | 1.6 | 5.6 | 0.3 | 1.1 |
Spur/branch length ratio | 3 | 12% | – | 20% | – | 16% | – | 4% | – | ||
Claw 2 heights | |||||||||||
Branch | 3 | 8.5 | – | 9.8 | 38.0 | – | 39.0 | 9.3 | 38.5 | 0.7 | 0.7 |
Spur | 3 | 1.2 | – | 1.4 | 4.8 | – | 5.2 | 1.3 | 5.0 | 0.1 | 0.3 |
Spur/branch length ratio | 3 | 13% | – | 16% | – | 14% | – | 2% | – | ||
Claw 3 heights | |||||||||||
Branch | 2 | 9.2 | – | 10.1 | 36.8 | – | 40.2 | 9.7 | 38.5 | 0.6 | 2.4 |
Spur | 2 | 1.0 | – | 1.8 | 4.0 | – | 7.2 | 1.4 | 5.6 | 0.6 | 2.2 |
Spur/branch length ratio | 2 | 11% | – | 18% | – | 14% | – | 5% | – | ||
Claw 4 heights | |||||||||||
Branch | 2 | 11.6 | – | 11.6 | 46.2 | – | 46.2 | 11.6 | 46.2 | 0.0 | ? |
Spur | 2 | 2.0 | – | 2.0 | 8.0 | – | 8.0 | 2.0 | 8.0 | 0.0 | ? |
Spur/branch length ratio | 2 | 17% | – | 17% | – | 17% | – | 0% | – |
Dorsal plates well-sclerotised as for a Pseudechiniscus species, clearly demarcated from each other, with Pseudechiniscus-type sculpturing, i.e. large endocuticular pillars protruding through the epicuticle and visible as dark dots in PCM (Fig.
Ventral cuticle with a faint species-specific pattern reaching the lateroventral sides of the body (Figs
Pedal plates and dentate collar IV absent; instead, large patches of pillars are present centrally on each leg (Fig.
Mature males (i.e. from the second instar onwards; measurements in Table
Juveniles. Unknown.
Larvae. Unknown.
Eggs. Unknown.
Measurements [in µm] of selected morphological structures of mature males of Pseudechiniscus asper mounted in Hoyer’s medium. Measurements of the holotype taken from
CHARACTER | ♂ | Holotype | |
---|---|---|---|
µm | sp | µm | |
Body length | 159 | 675 | 166 |
Scapular plate length | 23.5 | – | ? |
Head appendages lengths | |||
Cirrus internus | 11.4 | 48.5 | 8.0 |
Cephalic papilla | 4.7 | 20.0 | ? |
Cirrus externus | 14.8 | 63.0 | 12.0 |
Clava | 3.5 | 14.9 | 1.5 |
Cirrus A | 19.4 | 82.6 | 20.0 |
Cirrus A/Body length ratio | 12% | – | 12% |
Papilla on leg IV length | 3.7 | 15.7 | ? |
Claw 1 heights | |||
Branch | ? | ? | ca. 9.0 |
Spur | ? | ? | ? |
Spur/branch length ratio | ? | – | ? |
Claw 2 heights | |||
Branch | 11.1 | 47.2 | ca. 9.0 |
Spur | 0.9 | 3.8 | ? |
Spur/branch length ratio | 8% | – | ? |
Claw 3 heights | |||
Branch | 10.9 | 46.4 | ca. 9.0 |
Spur | ? | ? | ? |
Spur/branch length ratio | ? | – | ? |
Claw 4 heights | |||
Branch | 13.1 | 55.7 | ca. 11.0 |
Spur | 1.0 | 4.3 | ? |
Spur/branch length ratio | 8% | – | ? |
This is the third record of this very rare species, which, in addition to the type locality, has also been found on Mount Taibai, Shaanxi, China (
Taxa most similar to P. asper, i.e. those possessing pseudosegmental projections, can be easily distinguished from this species, based on the presence of striae (even rudimentary striae are absent in P. asper; see Fig.
ca. 40°54'03.6"N, 140°51'58"E, 30 m a.s.l.; Asamushi-Onsen Forest Park (Aomori, Northern Honshu, Japan); mosses from tree trunks. Collector: R.M. Kristensen. Holotype and allotype: mature female and male on slide JP.013.01. Eight juveniles on the slides JP.012.02–3, JP.013.03–4, JP.014.01–3, JP.015.01. Hologenophores: JP.012.02–3, JP.013.03–4. Holotype, allotype and the majority of paratypes (slides JP.012.02–3, JP.013.01, JP.013.03–4 and JP.015.01) are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków, Poland; other paratypes (slides JP.014.01–3; NHMD–669705–7) are deposited in the Natural History Museum of Denmark, University of Copenhagen, Denmark.
The name is a patronym honouring Shinta Fujimoto, an excellent Japanese tardigradologist specialising in marine Heterotardigrada. Noun in the genitive singular.
Mature female (i.e. the third or latter instar; measurements in Table
Measurements [in µm] of selected morphological structures of mature female (holotype) and male (allotype) of Pseudechiniscus shintai sp. nov. mounted in Hoyer’s medium.
CHARACTER | Holotype ♀ | Allotype ♂ | ||
---|---|---|---|---|
µm | sp | µm | sp | |
Body length | 196 | 735 | 178 | 754 |
Scapular plate length | 26.7 | – | 23.6 | – |
Head appendages lengths | ||||
Cirrus internus | 6.8 | 25.5 | 8.2 | 34.7 |
Cephalic papilla | 4.0 | 15.0 | 3.5 | 14.8 |
Cirrus externus | 12.8 | 47.9 | 12.5 | 53.0 |
Clava | 5.0 | 18.7 | 4.0 | 16.9 |
Cirrus A | 23.1 | 86.5 | 25.3 | 107.2 |
Cirrus A/Body length ratio | 12% | – | 14% | – |
Papilla on leg IV length | 3.1 | 11.6 | 2.3 | 9.7 |
Claw 1 heights | ||||
Branch | 8.7 | 32.6 | 7.3 | 30.9 |
Spur | 2.2 | 8.2 | 1.4 | 5.9 |
Spur/branch length ratio | 25% | – | 19% | – |
Claw 2 heights | ||||
Branch | 8.7 | 32.6 | 7.0 | 29.7 |
Spur | 2.0 | 7.5 | 1.6 | 6.8 |
Spur/branch length ratio | 23% | – | 23% | – |
Claw 3 heights | ||||
Branch | 8.8 | 33.0 | 7.2 | 30.5 |
Spur | 1.9 | 7.1 | 1.1 | 4.7 |
Spur/branch length ratio | 22% | – | 15% | – |
Claw 4 heights | ||||
Branch | 9.2 | 34.5 | 8.8 | 37.3 |
Spur | 1.7 | 6.4 | 1.8 | 7.6 |
Spur/branch length ratio | 18% | – | 20% | – |
Dorsal plates poorly sclerotised, but clearly demarcated from each other, with the Pseudechiniscus-type sculpturing, i.e. endocuticular pillars protruding through the epicuticle and visible as dark dots in PCM (Fig.
Ventral cuticle with a pronounced species-specific pattern reaching the lateroventral sides of the body (Figs
Pedal plates and dentate collar IV absent, instead large patches of pillars are present centrally on each leg (Fig.
Mature male (i.e. the second or latter instar; measurements in Table
Juveniles (i.e. the second instar; measurements in Table
Larvae. Unknown.
Eggs. Unknown.
Measurements [in µm] of selected morphological structures of juveniles of Pseudechiniscus shintai sp. nov. mounted in Hoyer’s medium (N – number of specimens/structures measured, RANGE refers to the smallest and the largest structure amongst all measured specimens; SD – standard deviation).
CHARACTER | N | RANGE | MEAN | SD | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
µm | sp | µm | sp | µm | sp | ||||||
Body length | 6 | 93 | – | 172 | 597 | – | 730 | 144 | 682 | 27 | 49 |
Scapular plate length | 7 | 13.2 | – | 24.1 | – | 21.7 | – | 3.6 | – | ||
Head appendages lengths | |||||||||||
Cirrus internus | 7 | 5.2 | – | 8.9 | 22.7 | – | 37.4 | 7.1 | 31.2 | 1.2 | 5.2 |
Cephalic papilla | 6 | 2.0 | – | 4.3 | 11.9 | – | 18.4 | 3.0 | 14.5 | 0.8 | 2.2 |
Cirrus externus | 7 | 6.1 | – | 12.1 | 41.9 | – | 51.7 | 10.0 | 46.8 | 1.9 | 3.6 |
Clava | 2 | 3.9 | – | 4.4 | 17.6 | – | 18.8 | 4.2 | 18.2 | 0.4 | 0.8 |
Cirrus A | 4 | 17.1 | – | 26.0 | 84.2 | – | 111.1 | 22.2 | 96.8 | 3.7 | 11.0 |
Cirrus A/Body length ratio | 3 | 12% | – | 16% | – | 14% | – | 2% | – | ||
Papilla on leg IV length | 4 | 2.9 | – | 3.9 | 12.6 | – | 16.5 | 3.3 | 14.3 | 0.5 | 1.6 |
Claw 1 heights | |||||||||||
Branch | 5 | 5.9 | – | 7.8 | 30.5 | – | 44.7 | 7.1 | 34.9 | 0.7 | 5.6 |
Spur | 5 | 0.9 | – | 1.7 | 5.9 | – | 7.4 | 1.4 | 6.7 | 0.3 | 0.5 |
Spur/branch length ratio | 5 | 15% | – | 23% | – | 20% | – | 3% | – | ||
Claw 2 heights | |||||||||||
Branch | 6 | 6.7 | – | 8.9 | 30.1 | – | 37.2 | 7.7 | 33.2 | 0.8 | 2.3 |
Spur | 6 | 1.1 | – | 1.7 | 5.1 | – | 7.1 | 1.4 | 5.9 | 0.2 | 0.8 |
Spur/branch length ratio | 6 | 16% | – | 20% | – | 18% | – | 2% | – | ||
Claw 3 heights | |||||||||||
Branch | 6 | 5.3 | – | 9.0 | 29.2 | – | 40.2 | 7.2 | 34.3 | 1.2 | 4.0 |
Spur | 6 | 1.0 | – | 1.8 | 5.5 | – | 7.6 | 1.4 | 6.7 | 0.3 | 0.9 |
Spur/branch length ratio | 6 | 18% | – | 21% | – | 19% | – | 1% | – | ||
Claw 4 heights | |||||||||||
Branch | 5 | 7.2 | – | 9.0 | 35.5 | – | 39.3 | 8.4 | 37.2 | 0.7 | 1.4 |
Spur | 5 | 1.4 | – | 2.1 | 6.0 | – | 9.2 | 1.7 | 7.5 | 0.3 | 1.2 |
Spur/branch length ratio | 5 | 16% | – | 23% | – | 20% | – | 3% | – |
Single haplotypes in 18S rRNA (MT645084, 900 bp), 28S rRNA (MT645082, 754 bp) and ITS-1 (MT645086, 622 bp), but two in COI (MT644270-1, 510 bp) were found.
The species was compared with the members of the suillus-facettalis complex (with hemispherical cephalic papillae) and other Pseudechiniscus species lacking pseudosegmental projections. P. shintai sp. nov. is differentiated from:
Moreover, the ventral pattern distinguishes P. shintai sp. nov. from all other species for which this character has been described. We used morphometric differences for comparisons only as a last resort as sample sizes for the majority of the specimens in the type series were small. Importantly, although
p-distances between the new species and the remaining Pseudechiniscus spp., for which COI sequences are available, ranged between 18.6% (P. suillus) and 29.3% (P. lacyformis). Intraspecific distance was equal to 0.2%.
The dorsal sculpturing of P. asper is particularly interesting morphologically, as large, roughly circular endocuticular pillars protrude through the epicuticle as isolated, solid bumps, unconnected by thin ridges – striae. In many other Pseudechiniscus species, striae are typical elements of the armour (e.g.
The recent studies on Pseudechiniscus imply that all previous records of putatively cosmopolitan species should be questioned and verified to ensure against misidentification (
Brian Blagden kindly proofread the manuscript. Diane Nelson, Atsushi Suzuki and Harry Meyer are gratefully acknowledged for the improvements made on the manuscript. The study was performed within the scope of the Preludium grant funded by the National Science Centre (grant no. 2019/33/N/NZ8/02777 to PG supervised by ŁM) and the Sonata Bis programme of the National Science Centre (grant no. 2016/22/E/NZ8/00417 to ŁM). Łukasz Michalczyk is acknowledged for advice and constant support. We owe our sincere thanks to the Museum für Naturkunde, Berlin, for covering the publication charge. The Authors declare no conflict of interest.