Research Article |
Corresponding author: Katarína Krajčovičová ( krajcovic.katarina@gmail.com ) Academic editor: Mark Judson
© 2020 Katarína Krajčovičová, Aleksandr Vladimirovich Matyukhin, Jana Christophoryová.
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.
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Krajčovičová K, Matyukhin AV, Christophoryová J (2020) Two new pseudoscorpion species (Pseudoscorpiones, Chthoniidae, Cheiridiidae) from the Tonga Islands, Polynesia, with a redescription of the genus Nesocheiridium. ZooKeys 927: 37-51. https://doi.org/10.3897/zookeys.927.49351
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The genera Tyrannochthonius Chamberlin, 1929 and Nesocheiridium Beier, 1957 are recorded from the Tonga Islands, Polynesia, for the first time. Tyrannochthonius eua sp. nov. is described from the island of Eua. Nesocheiridium onevai sp. nov. is described from the island of Onevai. This is the first discovery of a representative of the genus Nesocheiridium in more than 60 years. The holotype of the type species, Nesocheiridium stellatum Beier, 1957, is redescribed, allowing a better understanding of this poorly known genus. The genus Nesocheiridium is diagnosed by the following combination of characters: integument coarsely granulate, dorsally granulo-reticulate; vestitural setae either relatively long, with a leaf-like outline, or arcuate with a small spine; cucullus short; only 10 abdominal tergites visible in dorsal view; cheliceral rallum of four blades; venom apparatus present in both chelal fingers; fixed chelal finger with granulate swelling mesally and seven trichobothria; trichobothria ib and ist located distad of granulate swelling; eb and esb situated close together at the base of the finger; moveable chelal finger with two trichobothria.
Endemism, Nesocheiridium, Oceania, taxonomy, Tyrannochthonius
Polynesia is a subregion of Oceania, comprising more than a thousand islands spread across the central and southern Pacific Ocean. The small size of the islands and their isolation promote strong evolutionary selection (
The genus Tyrannochthonius is widely distributed in tropical and subtropical regions of the world. It is one of the largest chthoniid genera, with 130 described species. Most of these have restricted distributions, known from only a few locations. The available data indicate a tendency for short-range endemism of its species (
The genus Nesocheiridium was erected in the Cheiridiidae by
All specimens examined for this study had been preserved in 75% ethanol. They were studied as temporary slide mounts, prepared by immersing the specimens in lactic acid for clearing. After study, they were rinsed in water and returned to 75% ethanol, with the dissected portions placed in microvials.
Morphological and morphometric analyses were performed using a Leica DM1000 compound microscope with an ICC50 Camera Module (LAS EZ application, 1.8.0). Measurements were taken from digital images using the AxioVision 40LE application. Reference points for measurements follow
Terminology follows
The types of new species are deposited in the zoological collections of the Naturhistorisches Museum Wien, Austria (
See
Holotype
: Polynesia • ♂; Tonga, Eua [-21.387, -174.930]; 215 m a.s.l.; 11 Jul. 1980; Galina Fedorovna Kurcheva leg.; moss;
Adult male
(Figs
Dimensions (length/width or, in the case of the legs, length/depth) in mm. Body length 1.10. Pedipalp: trochanter 0.13/0.09, femur 0.37/0.09, patella 0.19/0.09, chela 0.57/0.11, hand 0.24/0.11, fixed finger 0.31, moveable finger 0.33. Chelicera 0.26/0.17, moveable finger 0.15. Carapace 0.38/0.39. Leg I: trochanter 0.09/0.08, femur 0.22/0.05, patella 0.11/0.04, tibia 0.13/0.04, tarsus 0.17/0.03. Leg IV: trochanter 0.11/0.09, femoropatella 0.32/0.17, tibia 0.24/0.07, metatarsus 0.12/0.06, tarsus 0.20/0.03.
The specific epithet refers to the island of Eua, on which this species occurs. It is used as a noun in apposition.
The presence of intercalary teeth on the fixed chelal finger but not on the moveable chelal finger is unusual in Tyrannochthonius species. However, a few other species possess this combination: T. convivus Beier, 1974, T. brasiliensis Mahnert, 1979, T. amazonicus Mahnert, 1979, T. rex Harvey, 1989, and T. swiftae Muchmore, 1993 (
Tyrannochthonius eua sp. nov., holotype male, dorsal A carapace B coxae C coxal spines D right chelicera E right chela, showing trichobothrial pattern F chaetotaxy of genital area (sternites II–III). Abbreviations: trichobothria of moveable chelal finger: t–terminal, b–basal, sb–subbasal, st–subterminal; trichobothria of fixed chelal finger: dx–duplex trichobothria, et–exterior terminal, it–interior terminal, est–exterior subterminal, ist–interior subterminal, esb–exterior subbasal, eb–exterior basal, isb–interior subbasal, ib–interior basal. Scale bars: 0.1 mm.
Small species, with adult body length ranging from 0.85 to 0.94 mm. Integument coarsely granulate, dorsally granuloreticulate. Vestitural setae relatively long, arcuate with a small spine, often covered by a fine exudate, giving them a leaf-like shape. Carapace narrowed towards anterior end, with short cucullus and a deep, submedian, transverse furrow. One pair of eyes. Cheliceral hand with four setae (seta ls absent), all acuminate. Galea long and slender, simple in male, with three terminal rami in female. Rallum of four blades, distal one enlarged and dentate. Ten abdominal tergites visible in dorsal view, I–IX divided. Ventral anal opening large and circular. Pedipalps densely and strongly granulate, including hand and the base of the fixed fingers, femur pedicellate. Fixed chelal finger with granulate swelling mesally, most distinct from ventro-lateral view. Chelal fingers slightly shorter than hand without pedicel. Venom apparatus present in both chelal fingers. Seven trichobothria present on fixed chelal finger, situated mainly in its basal half. Trichobothria ib and ist located distad of the granulate swelling, eb and esb situated close together subbasally. Moveable chelal finger with two trichobothria, situated in its basal half.
Nesocheiridium shares a combination of characters with most genera in the subfamily Cheiridiinae: reduced number of trichobothria on fixed chelal finger (seven at most) and moveable finger (two at most), four setae present on cheliceral hand, first blade of rallum enlarged, femur and patella of legs fused, tarsus of legs as about the same length as tibia (
Holotype
: Northern Mariana Islands • ♂; Saipan, Mount Marpi [15.283, 145.817]; 40 m a.s.l.; 01 Mar. 1945; Henry S. Dybas leg.; under stone;
Adult male
(Figs
Nesocheiridium stellatum, holotype male A carapace B, C details of granulation types on carapace D leaf-like seta E arcuate seta with a small spine F right chelicera G coxae H right palp minus chela I chelal fingers, ventro-lateral view, showing swelling on fixed finger J right chela K detail of granulation on chela L chaetotaxy of genital area (sternites II–III) M right leg I N right leg IV. Abbreviations as for Figure
Dimensions (length/width or, for legs, length/depth) in mm. Body length 0.94. Pedipalp: trochanter 0.14/0.10, femur 0.33/0.08, patella 0.26/0.09, chela 0.47/0.13, hand with pedicel 0.28/0.13, hand without pedicel 0.23, moveable finger 0.21. Chelicera: 0.08/0.05, moveable finger 0.07. Carapace 0.34/0.40. Leg I: trochanter 0.06/0.07, femoropatella 0.18/0.05, tibia 0.12/0.04, tarsus 0.13/0.03. Leg IV: trochanter 0.10/0.07, femoropatella 0.23/0.06, tibia 0.18/0.05, tarsus 0.17/0.03.
Some of the morphometric values given here differ slightly from the original description (
Holotype
: Polynesia • ♀; Tonga, Onevai [-21.087, -175.115]; 7 m a.s.l.; 10 Jun. 1980; Galina Fedorovna Kurcheva leg.; moss;
Adult female
(Figs
Nesocheiridium onevai sp. nov., holotype female A carapace (damaged part cross-hatched) B, C details of granulation types on carapace D right chelicera E rallum F coxae G right palp minus chela H chelal fingers, ventro-lateral view, showing swelling on fixed finger I right chela J detail of granulation on chela K chaetotaxy of genital area (sternites II–III) L right leg I M right leg IV. Abbreviations as for Figure
Pedipalp
(Fig.
Dimensions (length/width or, for legs, length/depth) in (mm). Body length 0.85. Pedipalp: trochanter 0.14/0.09, femur 0.26/0.08, patella 0.21/0.10, chela 0.39/0.15, hand with pedicel 0.21/0.15, hand without pedicel 0.19, moveable finger 0.18. Chelicera: 0.09/0.05, moveable finger 0.07. Carapace 0.28/0.39. Leg I: trochanter 0.05/0.05, femoropatella 0.15/0.05, tibia 0.11/0.04, tarsus 0.13/0.03. Leg IV: trochanter 0.10/0.06, femoropatella 0.19/0.05, tibia 0.15/0.04, tarsus 0.16/0.03.
The species epithet refers to the island Onevai, on which this species occurs. It is used as a noun in apposition.
The two species currently placed in the genus are easy to distinguish from each other by the form of the carapace (N. stellatum lacks a medial depression on the posterior disk, whereas N. onevai sp. nov. has a weak medial depression on the posterior disk); the shape of the palpal patella (not broadened in N. stellatum, versus markedly broadened mesally in N. onevai sp. nov.); the number of setae on the carapace (43 in N. stellatum, 30 in N. onevai sp. nov.); the number of marginal teeth on the fixed chelal finger (16 in N. stellatum, 10 in N. onevai sp. nov.); the shape of the setae on sternite VIII (leaf-like in N. stellatum, as opposed to acuminate in N. onevai sp. nov.); and the lengths of the palpal segments (femur 0.33 mm in N. stellatum, 0.26 mm in N. onevai sp. nov.; patella 0.26 mm in N. stellatum, 0.21 mm in N. onevai sp. nov.; hand with pedicel 0.28 mm in N. stellatum, 0.21 mm in N. onevai sp. nov.).
The original description of the genus Nesocheiridium was based on a single male of N. stellatum. The discovery of a new, congeneric species affords the opportunity to clarify the diagnostic characters of this inadequately known genus. The presence of a granulate swelling on the base of the fixed chelal finger is considered to be the main diagnostic character of Nesocheiridium. However, it is worth noting that, although this character has not previously been mentioned in descriptions of other Cheiridiinae, some drawings, such as those published for Neocheiridium corticum (Balzan, 1877) by
We are grateful to Petra Sierwald, Rudiger Bieler, Robin Delapena, and Stephanie Ware (Collaborative Invertebrate Laboratory at the Field Museum, Chicago) for their help and for taking images. We thank our colleagues Daniel Gruľa, Erika Igondová, and Dávid Selnekovič (Comenius University, Slovakia) for technical assistance with the photographs and map. Special thanks go to Galina Fedorovna Kurcheva who collected the material in Polynesia and Mark Stephen Harvey who encouraged us to do a better job. We are grateful to the reviewers, M.S. Harvey and Hajime Ohira, for valuable and constructive comments which improved the quality of the paper.