Research Article |
Corresponding author: Rodrigo Lopes Ferreira ( drops@dbi.ufla.br ) Academic editor: Ana Sofia P. S. Reboleira
© 2021 Ana Clara Moreira Viana, Rodrigo Lopes Ferreira.
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:
Viana ACM, Ferreira RL (2021) A new troglobitic species of Allochthonius (subgenus Urochthonius) (Pseudoscorpiones, Pseudotyrannochthoniidae) from Japan. Subterranean Biology 37: 43-55. https://doi.org/10.3897/subtbiol.37.58580
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Allochthonius (Urochthonius) yoshizawai sp. nov., found in Hiura-do Cave, a limestone cave located in the municipality of Kumakogen, Ehime Prefecture, Japan, is described. It can be distinguished from the consubgeneric species mainly by the carapacal chaetotaxy (6–2, 18), by the presence of 6 setae on the cheliceral palm, by the rallum with 11 blades, by the presence of 8 clavate coxal blades on coxae I, and by the decreased number and distinct shape of the chelal teeth. A redescription of the subgenus Urochthonius, and keys to the subgenera of Allochthonius and to the species and subspecies of Urochthonius are also provided, as well as some ecological remarks, a brief discussion on troglomorphisms for the subgenus, and potential threats for this species.
Cave, pseudoscorpions, taxonomy, troglomorphism
In East Asia, the pseudoscorpion family Pseudotyrannochthoniidae Beier, 1932 is represented by two genera, Allochthonius Chamberlin, 1929 and Pseudotyrannochthonius Beier, 1930 (
During an expedition to caves in Japan (carried out from September 5 to 15, 2017), a single pseudoscorpion was found, belonging to a new species herein described. The single male specimen belonging to the subgenus Urochthonius was found in Hiura-do Cave, a limestone cave located in Shikoku Island. The new species is considered troglobitic, and it shows a distinct combination of morphological features. It shares some characteristics with two consubgeneric species, A. (U.) ishikawai Morikawa, 1954 and A. (U.) brevitus Hu & Zhang, 2012.
It is important to point out that the subgeneric division of the genus Allochthonius, which is solely based on morphological characters (e.g. the absence or number of eyes) and typical habitat type, appears unstable and thus a taxonomic revision is imperative. However, while we recognize the need of further research on this matter, the description of a new species based on a single specimen, although oftentimes discouraged by researchers, can be of crucial importance, especially when taken into consideration species conservation. Furthermore, it is noteworthy that many troglobitic species, especially predators, can be extremely rare. Due to impacts on cave systems, a species may lose its habitat and become potentially extinct before its formal taxonomic description, as observed by
Fieldwork was carried out in September 2017 at Hiura-do Cave, a limestone cave located in the municipality of Kumakogen, Ehime Prefecture, Shikoku Island, Japan (Figs
More details on habitat are covered in a separate section (habitat and threats) later in the paper.
In order to properly observe taxonomic characters, the specimen and its dissected appendages were mounted in temporary cavity slides, using glycerin as medium. Photographs and measurements of body parts were taken with a Zeiss Axio Zoom.V16 stereomicroscope, using the software Zen 2.3. Drawings were prepared with a drawing tube on a Leica DM750 microscope equipped with phase contrast. For drawings, Kaiser’s glycerol gelatin was used instead of glycerin. This mounting media solidifies at cold temperatures, thus allowing the dissected body parts to be kept in a fixed position.
Description of coloration was based on photographs of the living specimen, which were taken with a Cannon SX50 camera. The terminology used in the description follows
Abbreviations used: For trichobothria: ib = interior basal; isb = interior sub-basal; ist = interior sub-terminal; it = interior terminal; eb = exterior basal; esb = exterior sub-basal; est = exterior sub-terminal; et = exterior terminal; b = basal; sb = sub-basal; st = sub-terminal; t = terminal.
Genus Allochthonius Chamberlin, 1929
subgenus Urochthonius Morikawa, 1954
Type species. Allochthonius (Urochthonius) ishikawai Morikawa, 1954.
Diagnosis (modified from
Holotype male (
The specific name is given in honor of Dr. Kazunori Yoshizawa, not only due to the assistance provided during fieldwork in Japanese caves, but also to his great contribution to the knowledge of arthropods, especially Psocodea.
Differing from the other members of subgenus Urochthonius by the following combination of characters: carapace with 18 setae (6 on anterior margin, 2 on posterior margin); cheliceral palm with 6 setae, fixed cheliceral finger with large basal tooth, rallum with 11 blades (each with fine barbules, the basal-most blade shorter than the others); coxa I with a spray of 8 clavate coxal blades (subequal in length) on a mound, bisetose intercoxal tubercle present between coxae III and IV; on the fixed chelal finger, 7 (8 on the right chela) acute, narrow, large, widely-spaced teeth; on the movable chelal finger, 10 acute, small, widely-spaced teeth; chelal teeth varying in size.
Troglomorphic habitus (Fig.
Carapace (Fig.
Chelicerae (Fig.
Allochthonius (U.) yoshizawai sp. nov., male holotype A right chelicera, showing detail of surface texture, antiaxial (slightly ventral) view B right chela, showing trichobothrial pattern and marginal teeth, antiaxial view C right cheliceral rallum D left palp, dorsal view E left leg IV, retrolateral view. Scale bars: 0.25 mm (A); 0.5 mm (B, D, E); 0.125 mm (C).
Tergites: Undivided; chaetotaxy uniseriate, I–XI 2: 2: 4: 6: 6: 7: 9: 10: 8: 5: 2. Anal operculum without dorsal setae.
Coxae: Palpal: manducatory process with two setae, apical seta reduced; rest of palpal coxae with three setae. Pedal: coxae I each with a spray of 8 clavate blades (Fig.
Genital operculum of male (Fig.
Sternites: Chaetotaxy II–XI 13: 16: 17: 15: 15: 15: 12: 10:–:2. Anal operculum with one pair of ventral setae.
Palp (Fig.
Leg IV (Fig.
Measurements (length/breadth or, for legs, length/depth in mm, ratios in parentheses): Body length 1.97. Carapace 0.55/0.51 (1.1). Palps: trochanter 0.29/0.16 (1.8), femur 0.91/0.14 (6.5), patella 0.31/0.13 (2.5), hand with pedicel 0.54/0.26 (2.0), movable finger length 0.78, chela with pedicel 1.39 (5.3). Leg I: femur 0.53/0.08 (6.4), patella 0.32/0.07 (4.8), femur/patella (1.6), tibia 0.26/0.06 (4.7), tarsus 0.56/0.06 (10.2). Leg IV: femur+patella 0.77/0.17 (4.4), tibia 0.57/0.09 (6.1), metatarsus 0.28/0.07 (3.8), tarsus 0.64/0.06 (11.5), tarsus/metatarsus (2.3).
1 | Four eyes well-developed, mostly free-living species | Subgenus Allochthonius |
– | Eyes completely absent or two rudimentary eyes, mostly cave-dwelling species | Subgenus Urochthonius |
1 | Two rudimentary eyes present | A. (U.) biocularis |
– | Eyes absent | 2 |
2 | Palpal femur stout, 3.9 times longer than broad | A. (U.) brevitus |
– | Palpal femur slender, 3.9–6.5 times longer than broad | 3 |
3 | Cheliceral palm with 6 setae, rallum with 11 blades | A. (U.) yoshizawai sp. nov. |
– | Cheliceral palm with 5 setae, rallum with 10 blades | 4 |
4 | Chelal fingers distinctly curved, fixed finger with 9 marginal teeth, movable finger with 11 marginal teeth | A. (U.) ishikawai shiragatakiensis |
– | Fixed chelal fingers not so curved, with 13–17 marginal teeth | 5 |
5 | Anterior margin of carapace with 10 setae | 6 |
– | Anterior margin of carapace with 8 setae | 7 |
6 | Chelal fingers with 13–14 marginal teeth; cheliceral movable finger with about 13 minute teeth | A. (U.) ishikawai deciclavatus |
– | Chelal fingers with about 16 marginal teeth; cheliceral movable finger with about 18 minute teeth | A. (U.) ishikawai kyushuensis |
7 | Body length 1.51–1.97 mm | A. (U.) ishikawai ishikawai |
– | Body length 2.31–2.38 mm | 8 |
8 | Carapace chaetotaxy 8–2, 24 | A. (U.) ishikawai uenoi |
– | Carapace chaetotaxy 8–2, 18 | A. (U.) ishikawai uyamadensis |
Hiura-do Cave is a limestone cave with approximately 160 meters of horizontal extent and two entrances (Fig.
Type locality and habitat of Allochthonius (U.) yoshizawai sp. nov. A Main cave entrance B map of Hiura-do Cave, showing the site (red star) where the specimen was found, as well as the entrances C general aspect of the cave conduit. The specimen was collected crawling on a damp wall D drainage system at the deepest portion of the cave.
Potential prey for the pseudoscorpion are mainly springtails (Entomobryomorpha and Onychiuridae), which are relatively abundant in the cave. Other troglobitic species observed in the cave during our visit included, besides the Collembola, the highly troglomorphic carabid beetle Nipponaphaenops erraticus Ueno, 1971, the staphylinid beetle Quedius sp., the Grylloblattodea Galloisiana (an undescribed species), and a Rhagidiidae mite.
The cave presents obvious signs of human visitation (there is an iron ladder installed from the upper to the lower level), but such visitors seem to be mostly speleologists, so no severe impacts were observed in the cave. The external environment is also well preserved, with a forest covering most of the landscape. Considering the well-preserved status of both the cave and the external landscape surrounding the cave, the species seems not to be seriously threatened at the moment.
Concerning Urochthonius spp., it is difficult to state with certainty whether some characteristics represent typical troglomorphisms found in other pseudoscorpions. Two species, A. (U.) biocularis Morikawa, 1956 and A. (U.) ishikawai, are cave-dwelling, found in Japan. One of the main differences regarding external morphology between A. (U.) biocularis and A. (U.) ishikawai is that the former bears two anterior rudimentary eyes (
Nonetheless, A. (U.) brevitus exhibits an array of characteristics that sets it apart from the hypogean species. Allochthonius (U.) brevitus is characterized by having generally stouter appendages. Particularly in reference to its palpal femur ratio (3.9 times longer than broad) (
Furthermore, although it may simply represent a dispersal-aiding trait, the considerably high level of chelal finger curvature could potentially represent a troglomorphism for the cave-dwelling species in the subgenus. When comparing the chelal fingers of hypogean species and the single epigean representative, A. (U.) brevitus, the former present generally curved fingers (
We note some inconsistencies in the measurements and ratios in the descriptions of A. (U.) biocularis and A. (U.) ishikawai kyushuensis Morikawa, 1960, regarding the palpal femur (
Allochthonius (U.) yoshizawai sp. nov. is markedly pale, as evidenced by the mostly translucent cuticle of the holotype, and also presents slender appendages (e.g. palpal femur 6.5 times longer than broad). The new species presents a combination of characters based on which distinction from the consubgeneric species can be easily made. Differences related to the carapacal chaetotaxy, number of setae on the cheliceral palm, number of rallum blades, and number of palp chela marginal teeth can be indicated.
Carapacal chaetotaxy: Urochthonius species show a range of 18–28 setae on the carapace (
Cheliceral traits: Allochthonius (U.) brevitus has 6 setae on the cheliceral palm (
Number of chelal teeth: Allochthonius (U.) ishikawai subspecies have a range of 9–17 teeth on the fixed chelal finger, and 11–17 teeth on the movable finger (
With regard to the subgenus Urochthonius, the troglobitic status of its representatives has not been considered in previous works. As outlined earlier, important morphological specializations to the subterranean environment (e.g. paleness) can be recognized in Urochthonius cavernicolous species. Hence, we argue that A. (U.) yoshizawai sp. nov. and the consubgeneric cave-dwellers are troglobitic.
Even when taking into account that A. (U.) ishikawai kyushuensis was recorded from six caves located in Kyushu and Honshu islands, inference of the troglobitic status for the subgenus as a whole is still plausible.
We thank the team of the Center of Studies on Subterranean Biology (especially Dr. Marconi Souza Silva), for help with field work; Dr. Marconi Souza Silva, for producing the distribution map; Yusuke Hara, Dr. Tadashi Komatsu and Dr. Kazunori Yoshizawa for the assistance given during the expedition, and the institutions that supported the study with funding for scholarships and infrastructure (FAPEMIG and VALE). The field trip in Japan was supported by JSPS research grant 15H04409 to KY. RLF is also grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico for financial support (CNPq grant n° 308334/2018-3). We also thank Dr. Mark Harvey, M. Sc. Charles D. R. Stephen and the anonymous reviewer, whose constructive comments and suggestions greatly improved the quality of this paper.