A new species of Ditha (Pseudoscorpiones, Chthoniidae, Tridenchthoniinae) from the Western Ghats of India, with an identification key for the genus

Kyung-Hoon Jeong; Danilo Harms; Jithin Johnson

doi:10.3897/zse.100.110020

Abstract

A new species of the pseudoscorpion genus Ditha Chamberlin, 1929, is described from Kerala State, India. A detailed morphological description, diagnostic features, and illustrations of Ditha (Paraditha) shivanparaensis Jeong, Harms & Johnson, sp. nov. are provided. The current distribution of all the known Ditha species is mapped, and an identification key for the genus is provided.

Key Words

Arachnida, Kerala, montane, morphology, taxonomy

Introduction

Tropical montane cloud forests or ‘sholas’ of the Western Ghats of India encompass unique ecosystems characterized by their high elevations (>1000 m) and isolated nature. These sholas are considered as isolated ‘islands’ that are surrounded by the vast ocean of low-altitude forests or grasslands (Robin et al. 2015). The biota of these so-called ‘sky islands’ provide excellent templates for studying endemism and investigating the factors driving diversification and adaptation in such specialized environments. Pseudoscorpions (order Pseudoscorpiones de Geer, 1778) are one such group of arachnids found in these ecosystems. Globally, ca. 4000 nominal species are described in 25 families, with India hosting ca. 160 described species (WPC 2023). Due to their specific microhabitat preferences and poor dispersal abilities, most leaf-litter dwelling species, particularly those belonging to the family Chthoniidae Daday, 1889, exhibit short-range distributions (Cosgrove et al. 2016; Johnson et al. 2022; Hlebec et al. 2023).

Tridenchthoniinae Balzan, 1892 is a chthoniid subfamily with 71 extant species in 15 genera and one extinct species (Chelignathus kochii Menge, 1854). Until recently, it was regarded as a distinct family within the Chthonioidea superfamily (Benavides et al. 2019). It differs from other chthoniid subfamilies in the presence of granulate carapace, spines on both coxa I and II, trichobothria ib and isb located basally or sub-basally on the chelal hand, and a galea with multiple ramifications in the juvenile stage (Morikawa 1960; Kennedy 1989). Tridenchthoniinae is divided into two tribes, Tridenchthoniini and Verrucadithini, and they can be distinguished by the shape of the marginal chelal teeth, being relatively acute and distinctly spaced in Verrucadithini, while they are closely contiguous in Tridenchthoniini (Chamberlin and Chamberlin 1945). Tridenchthoniini comprises nine genera; among these, the genus Ditha Chamberlin, 1929 is distributed from East Asia to Africa. It includes two subgenera, Ditha (Ditha) and Ditha (Paraditha) Beier, 1931, with seven species recorded in each subgenus. The subgenus Paraditha comprises seven species: D. laosana Beier, 1951, D. pahangica Beier, 1955, D. sumatraensis (Chamberlin, 1923) and D. tonkinensis (Beier, 1951) distributed in Southeast Asia; D. latimana (Beier, 1931) and D. sinuata (Tullgren, 1901) from Africa; and D. marcusensis (Morikawa, 1952) from East Asia (Fig. 1).

Figure 1.

Distribution of the Ditha (Ditha) and Ditha (Paraditha) species.

Hitherto, only two species of Tridenchthoniinae belonging to the genus Compsaditha Chamberlin, 1929 have been reported from India: Compsaditha indica Murthy, 1960, and C. camponota Sivaraman, 1980. Here, we present the first record of the genus Ditha (Paraditha) from India and describe a new species from the Southern Western Ghats (Kerala state) of India along with an identification key for the genus Ditha.

Materials and methods

The specimens used for this study are lodged in the following institutions: Museum of Nature, Hamburg – Zoology (ZMH, formerly Zoological Museum Hamburg) and the Arachnology Division of Sacred Heart College, Thevara, India (ADSH). All specimens were initially preserved in 100% ethanol, with DNA extracted from the legs of one paratype female, while the other specimens are stored in 75% ethanol.

All specimens were examined using a Leica M125C stereomicroscope in 75% ethanol. Images were captured using a BK Plus Lab System (Dun, Inc.) equipped with a Canon EOS 7D Mark II camera fitted with a microscopic lens (5X, 10X magnification) using the software CAPTURE ONE PRO 9.3 64 Bit (v.9.3.0.85) and stacked using Zerene Stacker, and a Leica DMC4500 digital camera attached to a Leica M205A stereomicroscope, using the program, LEICA APPLICATION SUITE X (LASX), ver. 3.0.1. LASX was also used for taking the measurements. Mensuration and terminology largely follow Chamberlin (1931), with some minor modifications to the terminology of the trichobothria (Harvey 1992), chelicera (Judson 2007), and appendages (Harvey et al. 2012). Scanning electron micrographs were obtained with a Hitachi TM4000Plus scanning electron micrograph (SEM) system. Illustrations were created using ADOBE ILLUSTRATOR 2023 and edited with ADOBE PHOTOSHOP 2023. The distribution map was made using QGIS 3.22.10. Abbreviations used for chelal trichobothria: b – basal, sb – subbasal, st – subterminal, t – terminal, ib – internal basal, isb – internal subbasal, eb – external basal, esb – external subbasal, it – internal terminal, ist – internal subterminal, et – external terminal, est – external subterminal, xs – duplex trichobothria; leg segments: tr – trochanter, fe – femur, pa – patella, ti – tibia, mt – metatarsus, ta – tarsus; cheliceral seta: as – accessory setae.

Taxonomy

Family Chthoniidae Daday, 1889

Subfamily Tridenchthoniinae (Balzan, 1892)

Remarks

Balzan (1892) proposed the family Tridenchthoniidae to include the species Tridenchthonius parvulus Balzan, 1887 from Paraguay which possessed triple galea in the chelicera. However, Hansen (1894) considered this species to be an unusual Chthonius and reduced the taxon to the subfamily Tridenchthoniinae. Since then, the taxonomic status of the group has undergone several changes. Chamberlin (1929) in his revised classification scheme for pseudoscorpions, proposed a new subfamily Dithinae Chamberlin, 1929 to include the new genus Ditha Chamberlin, 1929. Dithinae chthoniids closely resemble Tridenchthoniinae, except that they include non-galeate forms, but they differ from members of Chthoniinae proper in the characters such as the presence of coxal spines (of single simple type) on coxa I and II and the patella of leg IV being distinctly longer in relation to the femur. Chamberlin (1931) later raised this group to the family status. However, without providing proper justification, Beier (1932) reduced the family to the subfamily status and later to Dithiidae again. However, recognizing Balzan’s species T. parvulus as a Dithiidae member, Chamberlin and Chamberlin (1945) proposed the family Dithiidae as a junior synonym of Tridenchthoniidae. Finally, in a recent study on pseudoscorpion transcriptomics (Benavides et al. 2019), the group was again reduced to a subfamily within Chthoniidae that now includes Tridenchthoniinae as a subfamily, alongside the Chthoniinae and Lechytiinae.

Genus Ditha Chamberlin, 1929

Type species

Ditha elegans Chamberlin, 1929.

Diagnosis

The genus Ditha can be diagnosed by the following combination of characters: tergites with biseriate setae; carapace with more than 50 setae; trichobothria st and t more than one areolar diameter apart, and triple galea in the juvenile stage. Ditha is divided into two subgenera, Ditha (Ditha) and Ditha (Paraditha). The subgenera Paraditha and Ditha can be differentiated based on the intercoxal tubercle and the number of accessory setae on the cheliceral palm (Beier, 1955). In Ditha, the intercoxal tubercle is strongly distinct and 10–12 accessory setae are present on the cheliceral palm, while the intercoxal tubercle is indistinct or even absent in Paraditha and only 1–2 accessory seta present on the cheliceral palm.

Ditha (Paraditha) shivanparaensis sp. nov.

https://zoobank.org/879135E3-C951-4A67-9FF8-4233D198E34B

Figs 1, 2, 3, 4

Type material

Holotype (Fig. 2A, B). Female (ADSH PST0001. INDIA: Kerala: Shivanpara, Mathikettan Shola National Park, Kerala, Idukki, 9°58'05.1"N, 77°13'43.5"E, altitude 1072 m, litter sample (sifting and Berlese trap), J. Johnson leg.

Paratypes (Fig. 2C, D): 3 females (ADSH PST0003, ADSH PST0004, ZMH-A0013527) and one male (ADSH PST0002), same data as holotype.

Figure 2.

Habitus of Ditha shivanparaensis sp. nov. A. Female holotype, dorsal view; B. Female holotype, ventral view; C. Male paratype, dorsal view; D. Male paratype, ventral view. Scale bars: 1 mm.

Etymology

This species is named after the hill ‘Shivanpara’ in the Mathiketan Shola National Park, where all specimens were collected.

Diagnosis

Within the subgenus Paraditha, Ditha shivanparaensis sp. nov. closely resembles D. tonkinensis Beier, 1951 found in Vietnam in having an indistinct intercoxal tubercle between coxa III and IV, and presence of eight setae on the posterior margin of the carapace. However, the new species differs from D. tonkinensis and from all other species within the subgenus in having two accessory setae on the cheliceral palm. Ditha shivanparaensis sp. nov. also bears similarity to Ditha (Ditha) proxima (Beier, 1951) from Vietnam in terms of having two accessory setae on the cheliceral palm and 45–47 marginal teeth on the movable chelal finger. However, it differs from the latter in possessing 14 setae on the anterior margin of the carapace (as opposed to 10 setae in D. proxima) and by the positioning of st, i.e., halfway between sb and t (whereas st is much closer to sb in D. proxima).

Description

Female, adult (holotype, Fig. 2A, B).

Colour. Uniformly orange-brownish, the legs lighter than the body.

Chelicera (Figs 3F, H, 4D, E). Cheliceral palm coarsely granulate and with seven setae (including two accessory setae), movable finger with one seta in medial position and seven marginal teeth, inner margin granulate; fixed finger with seven marginal teeth, the terminal one larger than the others (Fig. 3H); with two dorsal lyrifissures; rallum with ten blades (Figs 3F, 4E); serrula exterior with 16 blades of similar size.

Figure 3.

Drawings of Ditha shivanparaensis sp. nov. (all paratypes unless mentioned otherwise) A. Carapace, dorsal view; B. Leg IV; C. leg I; D. Coxa; E. Coxal spines; F. Rallum; G. Left chela from the lateral; H. Cheliceral, dorsal view, two accessory setae in the box; I. Male genital area external view; J. Female genital area external view (holotype). Scale bars: 0.5 mm (A–D, G); 1 mm (E–F); 2 mm (H–J).

Figure 4.

Ditha shivanparaensis sp. nov. A. Carapace, dorsal view; B. Left chela, lateral view; C. Left chela, dorsal view; D. Cheliceral, dorsal view; E. Rallum; F. Coxa (intercoxal tubercle in the circle); G Coxal spine. Scale bars: 200 µm (A–C); 100 µm (D, F); 30 µm (E); 50 µm (G).

Pedipalp (Figs 3G, 4B, C). Trochanter 1.44 times, femur 3.54 times, patella 1.83 times, chela (with pedicel) 3.79 times, hand 1.51 times longer than broad, movable finger 1.54 times longer than hand. Femur, patella, chela smooth. Fixed chelal finger with six trichobothria, movable finger with four trichobothria, ib and isb situated basally on the dorsum of the chelal hand; sb, st, and t located separately from b; sb, st and t all spaced more than one areolar distance; st slightly closer to sb than t; eb, esb and ist forming a group at basal to subbasal position; esb slightly closer to ist than eb; est and it positioned at the median on the fixed finger; et closely located with xs, almost less than one areolar distance (Figs 3G, 4B). Four lyrifissures on the dorsum of fixed chelal finger, one on the basal dorsum of chelal hand. Both fingers with small juxtadentate teeth; fixed finger with 55 triangular and retrorse teeth; movable finger with 47 rounded teeth.

Cephalothorax (Figs 3A, D, E, 4F, G). Carapace 1.04 times longer than broad sub-rectangular; lateral margins almost parallel but slightly wide at the base; coarsely granulate, without furrows; four corneate eyes; anterior margin serrated; epistome small and serrated; with 94 setae; 14 setae on the anterior margin, eight setae on posterior margin; setae short and acuminate; with ten lyrifissures, three each on the sides near the anterior margin, one between each eye, and one on each side situated near the posterior margin (Fig. 3A). Manducatory process with one long, acuminate setae, remainder of maxilla with ten setae; four lyrifissures on the maxilla. Coxal chaetotaxy: 10: 11: 11: 20 (Fig. 3D). Coxa I with ca. 5–6 spines, each spine serrated terminally, and ca. 2–3 spines from one base; coxa II with ca. 5–6 spines (Figs 3E, 4E, F); each spine serrated from the medial. Intercoxal tubercle indistinctly present between coxa III and IV, seta weakly present (Fig. 4F).

Abdomen. Pleural membrane papillostriate, tergites undivided, but sternites III–IV partially divided; setae biseriate and acuminate. Tergal chaetotaxy, 14: 23: 23: 25: 26: 24: 24: 25: 21: 17: 13: 0. Sternal chaetotaxy, 15: 10: 8: 8: 8: 8: 8: 9: 12: 4: 2. Sternite I with 4 setae in the genital opening area.

Legs (Fig. 3B, C). Leg I: trochanter 1.18 times, femur 3.87 times, patella 2.98 times, tibia 2.56 times, tarsus 5.93 times longer than broad, leg IV: trochanter 1.48 times, femur 2.75 times, tibia 3.44 times, metatarsus 2.57 times, tarsus 7.00 times longer than broad; leg IV: trochanter 1.67 times, femur 2.39 times, tibia 3.47 times, metatarsus 2.57 times, tarsus 5.49 times longer than broad. Tarsus of leg IV longer than the metatarsus; arolium undivided and shorter than the claws; pseudotactile seta located basally on leg I patella and medially on leg IV metatarsus.

Genitalia (Fig. 3J). Typical shape of the genus Ditha. 15 setae in the genital opening area, including nine setae on the center of the opening and three setae each on either side of the opening; ten setae on the sternite III; six setae on the anterior part of sternite III; four setae on the posterior region, and two setae each on the part of sternite III.

Dimensions (in mm). Body length 1.47; Pedipalp: trochanter 0.22/0.15, femur 0.48/0.13, patella 0.27/0.15, chela (with pedicel) 0.72/0.19, movable finger 0.45, hand 0.29/0.19; Chelicera: total 0.32/0.18, movable finger 0.17; Cephalothorax: Carapace 0.47/0.45, anterior eye 0.005, posterior eye 0.004; Leg I: trochanter 0.13/0.11, femur 0.27/0.07, patella 0.19/0.06, tibia 0.15/0.06, tarsus 0.27/0.05; Leg IV: trochanter 0.16/0.11, femur + patella 0.47/0.17, tibia 0.33/0.10, metatarsus 0.15/0.06, tarsus 0.28/0.04.

Male, adult (paratype, Fig. 2 C, D).

Same as the holotype, except slightly smaller (body length 1.291 mm).

Pedipalp. Trochanter 1.46 times, 3.54 times, patella 1.87 times, chela (with pedicel) 3.85 times, hand 1.47 times longer than broad, movable finger 1.56 times longer than hand; fixed finger with 50, movable finger with 48 teeth.

Cephalothorax. Carapace 1.06 times longer than broad; with 92 setae; 14 setae on the anterior margin, eight setae on the posterior margin; Coxal chaetotaxy: 10: 11: 11: 20. Coxa I with ca. 5–6 spines.

Abdomen. Tergal chaetotaxy, 10: 14: 15: 16: 19: 19: 19: 18: 16: 15: 13: 0. Sternal chaetotaxy, 10: 36: 6: 8: 10: 8: 13: 13: 11: 5: 2. Sternite II with nine total setae including six setae near the genital opening, sternite III with 38 total setae including 22 setae near the genital opening.

Legs. Leg I: trochanter 1.33 times, femur 3.65 times, patella 2.92 times, tibia 2.58 times, tarsus 5.80 times longer than broad; leg IV: trochanter 1.67 times, femur 2.39 times, tibia 3.47 times, metatarsus 2.57 times, tarsus 5.49 times longer than broad.

Genitalia (Fig. 3I). Typical shape of the genus Ditha. 15 setae in the genital opening area, including nine on the center of the opening and three each on either side of the opening; ten setae on the sternite III; six setae on the anterior part of sternite III; four setae on the posterior region, and two setae each on the part of sternite III.

Dimensions (mm). Body length 1.29. Pedipalp: trochanter 0.19/0.13, femur 0.44/0.12, patella 0.24/0.13, chela (with pedicel) 0.64/0.17, movable finger 0.38, hand 0.24/0.17; Chelicera: total 0.30/0.16, movable finger 0.17; Cephalothorax: Carapace 0.42/0.39, anterior eye 0.005, posterior eye 0.004; Leg I: trochanter 0.12/0.09, femur 0.24/0.07, patella 0.16/0.06, tibia 0.39/0.09, tarsus 0.24/0.04; Leg IV: trochanter 0.18/0.11, femur + patella 0.40/0.17, tibia 0.31/0.09, metatarsus 0.14/0.05, tarsus 0.26/0.05.

Variation of female paratypes

(n=2). Pedipalp. Trochanter 1.44–1.46 times, femur 3.46–3.68 times, patella 1.85–1.98 times, chela (with pedicel) 3.65–3.74 times, hand 1.48–1.52 times longer than broad, movable finger 1.43–1.44 times longer than hand. Movable finger with 48, fixed finger with 53–54 marginal teeth.

Cephalothorax. Carapace 1.04 times longer than broad. 96–100 setae.

Abdomen. Tergal chaetotaxy, 13–14: 21–23: 22–24: 24–25: 24–25: 25: 25–26: 23–25: 18: 15–16: 14–15: 0. Sternal chaetotaxy, 10: 10: 8: 7–8: 9–11: 8–10: 8–9: 10: 11–13: 4: 2.

Legs. Leg I: trochanter 1.20–1.34 times, femur 3.60–3.93 times, patella 2.61–2.64 times, tibia 2.47–2.77 times, tarsus 5.88–6.08 times longer than broad, leg IV: trochanter 1.59–1.66 times, femur 2.38–2.53 times, tibia 3.40–3.55 times, metatarsus 2.17–2.29 times, tarsus 5.39–6.14 times longer than broad.

Dimensions (mm): Body length 1.33–1.41; Pedipalp: trochanter 0.21–0.22/0.15, femur 0.48–0.51/0.13–0.15, patella 0.28–0.30/0.15, chela 0.71–0.73/0.19–0.20, movable finger 0.41–0.43, hand 0.29–0.30/0.19–0.20; Chelicera: total 0.29–0.31/0.18–0.19, movable finger 0.18–0.19; Cephalothorax: carapace 0.46–0.47/0.45, anterior eye 0.005–0.006, posterior eye 0.004; Leg I: trochanter 0.12–0.13/0.10, femur 0.28/0.07–0.08, patella 0.17–0.19/0.07, tibia 0.14–0.16/0.06, tarsus 0.27/0.04–0.05; Leg IV: trochanter 0.21/0.13, femur + patella 0.43–0.44/0.17–0.18, tibia 0.35–0.37/0.10–0.11, metatarsus 0.14–0.15/0.06–0.07, tarsus 0.27–0.30/0.05.

Distribution

Currently known only from the type locality.

Habitat

The species was collected from moist leaf litter of montane ‘shola’ forests of the Mathiketan Shola National Park and is probably endemic to this mountain, although more field sampling is required to verify this.

Erratum

The sequences with GenBank accession numbers OM792092.1, OM832661.1 and OM876917.1, previously attributed to the genus Compsaditha by Johnson et al. (2022), actually belong to the newly discovered species described herein as Ditha shivanparaensis sp. nov.

Key to the species of Ditha

1	Intercoxal tubercle distinct; 10–12 accessory seta positioned on the cheliceral palm	2, subgenus Ditha
–	Intercoxal tubercle indistinct or absent; 1–2 accessory seta positioned on the cheliceral palm	9, subgenus Paraditha
2	Cheliceral palm with less than six accessory setae	3
–	Cheliceral palm with more than six accessory setae	4
3	Carapace with less than 100 setae	D. proxima (Beier, 1951) (Vietnam)
–	Carapace with more than 100 setae	D. ogasawarensis Sato, 1981 (Japan)
4	Carapace with less than 150 setae	5
–	Carapace with more than 150 setae	6
5	12 setae on the anterior margin of the carapace	D. novaeguineae Beier, 1965 (Papua New Guinea)
–	14 setae on the anterior margin of the carapace	D. palauensis Beier, 1957 (Palau)
6	Tergite I with 12 setae in male	7
–	Tergite I with 21 setae in male	D. elegans Chamberlin, 1929 (Indonesia)
7	14 setae on the anterior margin of the carapace	D. philippinensis Chamberlin, 1929 (Philippines)
–	16 setae on the anterior margin of the carapace	D. loricata Beier, 1965 (Indonesia)
8	Intercoxal tubercle absent	10
–	Intercoxal tubercle indistinct	12
9	Intercoxal tubercle absent	10
–	Intercoxal tubercle indistinct	12
10	Posterior margin of carapace with 8 setae	11
–	Posterior margin of carapace with 14 setae	D. marcusensis (Morikawa, 1952) (Japan)
11	Carapace more than 70 setae	D. pahangica Beier, 1955 (Malaysia)
–	Carapace fewer than 70 setae	D. sumatraensis (Chamberlin, 1923) (Indonesia)
12	Carapace with more than 100 setae	D. laosana Beier, 1951 (Laos)
–	Carapace with fewer than 100 setae	13
13	Carapace with more than 70 setae	14
–	Carapace with fewer than 70 setae	D. sinuata (Tullgren, 1901) (Cameroon)
14	Pedipalpal femur at least 4 times longer than broad	D. latimana (Beier, 1931) (Tanzania)
–	Pedipalpal femur at least 4 times longer than broad	15
15	Chelicera with 1 accessory setae	D. tonkinensis Beier, 1951 (Vietnam)
–	Chelicera with 2 accessory setae	D. shivanparaensis sp. nov. (India)

Acknowledgements

KHJ thanks Jung-sun Yoo (National Institute for Biological Resources, Korea) for introducing him to Danilo Harms and facilitating his research stay at the Museum of Nature, Hamburg – Zoology. KHJ also extends deep gratitude to his parents, Aekyung Lim and Hyuncheol Jeong for their wholehearted support of his research stay in Hamburg, Germany. JJ thanks the Deutscher Akademischer Austauschdienst (DAAD), Germany for funding his research stay in Germany (No. 57440919, 2019/20). The authors are also grateful to Stephanie F. Loria and Nadine Dupérré (both from Hamburg) for their help with distribution mapping and imaging, respectively, and the forest department of the Indian state of Kerala and the National Biodiversity Authority, Govt. of India (No. NBA/Tech Appl/9/Form B-92/19/19-20/676 dated 20.06.2019) for providing necessary permits for the study. Furthermore, the authors also thank the academic editor and the two reviewers, one anonymous and the other Mark Harvey, for their valuable comments and suggestions that have improved this manuscript.

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