Taxonomic re-appraisal of Scolopocryptops quadristriatus (Verhoeff, 1934) and a description of a new species from Japan and Taiwan (Chilopoda, Scolopendromorpha, Scolopocryptopidae)

Centipedes of the genus Scolopocryptops Newport, 1844 are blind species mostly described from the New World and East Asia. In this study, a Japanese species, S. quadristriatus (Verhoeff, 1934), which is characterised by four longitudinal keels on the tergites, is re-described, based on the likely holotype preserved in the Zoologische Staatssammlung München and specimens newly collected from near the type locality. In addition, S. longisetosus sp. nov. , a new species that bears tergal keels like S. quadristriatus , is de - scribed from the Ryukyu Islands in Japan and Taiwan. Although the presence of four keels on tergites is unique to these two species, phylogenetic analyses using nuclear and mitochondrial markers showed that S. longisetosus sp. nov. is not sister to S. quadristriatus . The obtained phylogeny indicates that the tergal longitudinal keels evolved in parallel within Scolopocryptops or that the presence of keels represents a plesiomorphic character of the clade containing these species.


Introduction
Scolopocryptops Newport, 1844 is a centipede genus that mostly inhabits epigean habitats in North and South America, West Africa, East Asia and Vietnam and species have been also recorded from India, the Philippines, Indonesia, New Guinea and Fiji (Chagas- Jr et al. 2023;Le et al. 2023).The genus currently comprises 33 species and subspecies, which are classified into two groups: the Asian/North American group and the Neotropical/Afrotropical group (Chagas-Jr 2008;Edgecombe et al. 2012;Vahtera et al. 2013;Chagas-Jr et al. 2023;Le et al. 2023;Jonishi and Nakano 2023).Recent studies showed that the Asian/North American group consists of two lineages: a lineage composed of S. elegans (Takakuwa, 1937) and its closest relatives (hereinafter the elegans lineage), which is known from Far East Asia and a lineage including the rest of the Asian and North American species (hereinafter, the ex-elegans lineage) (Jonishi andNakano 2022, 2023).
Scolopocryptops centipedes are characterised by a distinctive kind of collared antennal setae, the absence of eyes, 23 leg-bearing segments (except for S. sukuyan Chagas-Jr, Edgecombe & Minelli, 2023, which has 25 segments) and an ultimate leg prefemur with one dorso-medial and/or one ventral spinous process (Koch et al. 2010;Chagas-Jr et al. 2023;Le et al. 2023).Several Asian/North American species, for example, S. sexspinosus (Say, 1821) and S. spinicaudus Wood, 1862, are distinguished from others by the absence of complete paramedian sutures on tergites (Le et al. 2023).Amongst them, the Japanese S. quadristriatus (Verhoeff, 1934) bears four longitudinal keels on its tergites, which is a specific character that distinguishes this species from all other Scolopocryptops (Verhoeff 1934;Takakuwa 1940;Shinohara 1984;Le et al. 2023).After it was described as Otocryptops sexspinosus quadristriatus, based on a specimen from the vicinity of Tokyo, S. quadristriatus has been recorded from several localities in Honshu, the Izu Islands and Kyushu in the Japanese Archipelago (Shinohara 1949;Takashima and Shinohara 1952;Miyosi 1953;Takano 1973).Phylogenetic analyses indicated that this species belongs to the ex-elegans lineage (Jonishi and Nakano 2022).As summarised by Le et al. (2023), however, the taxonomic status of S. quadristriatus remains uncertain because only a low resolution of morphological features has been reported (Verhoeff 1934;Takakuwa 1939Takakuwa , 1940;;Shinohara 1984).
In this study, a re-description of S. quadristriatus, based on the likely holotype is provided and newly-obtained specimens from near the type locality and adjacent areas were also investigated.In addition, several unidentified Scolopocryptops specimens obtained from the Ryukyu Islands in southern Japan and Taiwan have been studied.These individuals are morphologically similar to S. quadristriatus, but differ in several characters.Based on both morphological examination and phylogenetic analyses using nuclear and mitochondrial markers, these specimens are described as a new species herein.

Specimen collection and morphological observation
A specimen labelled as "Otocryptops sexspinosus quadristriatus" deposited at the Zoologische Staatssammlung München (ZSM A20051244), which is likely to represent the holotype of this taxon, was examined.Additional specimens of S. quadristriatus were collected from several localities in Tokyo and adjacent areas in eastern Honshu, Japan (Fig. 1).A total of 21 unidentified Scolopocryptops individuals were also collected from Okinawa, Ishigaki and Yonaguni Islands in the Ryukyu Islands and Hsinchu and Nantou Counties in Taiwan (Fig. 1).Specimens were placed in 30% ethanol for several minutes, fixed in 80% or 99% ethanol and then preserved in 75% ethanol.Ultimate leg-bearing segments of several specimens were dissected to examine genital segments.(Verhoeff, 1934) and S. longisetosus sp.nov. in the present study.Purple circles: S. quadristriatus; red diamonds: S. longisetosus sp.nov.; black diamonds: localities of the sequence data of Taiwanese "S.capillipedatus" (= S. longisetosus sp.nov.) obtained from INSD.Locality numbers (Q1-Q3 and L1-L6) are shown in Table 1 and Fig. 13.All specimens were observed using a Leica M125C stereoscopic microscope with a drawing tube (Leica Microsystems, Wetzlar, Germany).The specimens were photographed using a Sony a6500 digital camera and a 65 mm macro lens and a Leica MC170 HD digital camera mounted on the Leica M125C.Images captured with the Leica MC170 were processed using Leica Application Suite v. 4.1.2.Specimens examined are deposited in the Zoological Collection of Kyoto University (KUZ).

Molecular analyses
In addition to the 42 sequences obtained in this study, 39 sequences of Japanese and Taiwanese Scolopocryptops species (Jonishi andNakano 2022, 2023) and 31 sequences of scolopocryptopid species retrieved from the INSD were included in the taxon set (Table 1).
The nuclear ITS2 sequences were aligned using MAFFT L-INS-i (Katoh and Standley 2013); the nuclear 28S and the mitochondrial 16S sequences were aligned using MAFFT Q-INS-i (Kuraku et al. 2013;Katoh et al. 2019) considering the RNA secondary structure; non-conserved regions of these genes were trimmed by Gblocks v. 0.91b (Castresana 2000).The mitochondrial COI sequences showed no indels; thus, alignment was straightforward.The first four COI positions were excluded from the analyses because this portion was missing in most of the sequences.The concatenated sequences yielded 2510 bp of aligned positions comprising 780 bp of ITS2, 536 bp of 28S, 654 bp of COI and 540 bp of 16S.
Uncorrected pairwise distances for COI sequences (590-654 bp) were calculated with MEGA 11 (Tamura et al. 2021), with pairwise deletion of missing data (Suppl.material 2).Type specimen.Otocryptops s. quadristriatus was described, based on a single specimen from the vicinity of Tokyo, without any information on the collector, collecting date or deposition of the specimen (Verhoeff 1934).Most of the Verhoeff's specimens are now kept at the Zoologische Staatssammlung München (ZSM), the Museum für Naturkunde (MfN) and the Naturhistorischen Museums Wien (NHMW) (Melzer et al. 2011).

Taxonomy
A specimen of O. s. quadristriatus is deposited at the ZSM, but neither MfN nor NHMW have specimens labelled as O. s. quadristriatus (Moritz and Fischer 1979;Schileyko and Stagl 2004).ZSM A20051244 (Fig. 2) is, thus, the only specimen of O. s. quadristriatus remaining within the Verhoeff's collection and is supposed to be the holotype of this nominal taxon, although the original label and collection data of this specimen are unavailable (Stefan Friedrich, personal communication).Its cephalic capsule, maxillae and left ultimate leg had been preserved in a separate vial (Fig. 2A); the body had been cut into two parts on leg-bearing segment 8 (Fig. 2B); its ultimate leg-bearing segment had been dissected.Additionally, its left legs 6, 8, 12, 14, 15, 17, 18, 20 and 22; right legs 3, 8, 12-18 and 20-22; and right ultimate leg had been lost or loosened; its left leg 16 was loosened during observation by the first author.Morphological features of the likely holotype are consistent with the original description and specimens newly obtained in this study.Thus, a description, based on both ZSM A20051244 and our specimens, is provided below.Shinohara (1982) stated that a Japanese myriapodologist, the late Dr Yoshioki Takakuwa, sent a specimen of O. s. quadristriatus to Verhoeff.Given that Verhoeff also received other chilopod specimens from Takakuwa (e.g.Verhoeff (1934Verhoeff ( , 1935Verhoeff ( , 1937)), it is plausible that the likely holotype was also dispatched from Takakuwa to Verhoeff.
Additional material.Japan -    Colour in life yellowish-brown with dark pigment on two basal antennal articles, purplish on subsequent articles; reddish-brown on forcipules; reddish-brown with dark pigment on anterior, lateral and posterior margins of cephalic plate, tergites 1, 22 and 23; purplish dark brown on tergites 2-21; legs and ultimate legs brownish-yellow or orange with bluish dark pigment (Fig. 3B).Colour in ethanol slightly greenish on tergites and legs (Fig. 6A).
Second maxillae article 2 with elongated and semi-transparent [dark brown] dorsal spur distally; dorsal brush with transparent margination; pretarsus consisting of dark brown basal and semi-transparent short apical parts (Fig. 5B, C).Forcipular coxosternite and trochanteroprefemora sparsely punctate, coxosternite with median suture and transverse sutures cross median one on anterior third of coxosternite (Fig. 5D); trochanteroprefemur with small and blunt black process with basal suture (Fig. 5D); anterior margin of coxosternite strongly sclerotised and slightly convex, divided into two low lobes by median diastema (Fig. 5D).
Legs almost lacking setae [sparse minute setae present in several specimens]; tarsi of legs 1-21 undivided; legs 1-20 with lateral and ventral tibial spurs and tarsal spur, leg 21 with tibial spur and tarsal spur; leg 22 with tarsal spur only; all legs with two accessory spines.
Distribution.This species has been recorded from Honshu and the Izu Islands and is abundant in Tokyo and adjacent areas (Takakuwa 1939(Takakuwa , 1940;;Shinohara 1949;Takashima and Shinohara 1952;Takano 1973).Miyosi (1953) recorded S. quadristriatus from Nagasaki in Kyushu, but this species was not obtained during the survey conducted by the first author in Nagasaki and adjacent localities (25-27 July 2023).
Availability of "quadristriatus" based on Takakuwa's works.The name "Otocryptops sexspinosus quadristriatus", which was attributed to Verhoeff, was introduced by Takakuwa's two works (Takakuwa 1933a, b) before its formal description by Verhoeff in 1934.However, we herein decide that neither Takakuwa (1933a) nor Takakuwa (1933b) made the species-group name "quadristriatus" available."Otocryptops sexspinosus quadristriatus Verh" first appeared in Takakuwa (1933a: 11), who intended to provide general anatomical features of Scolopocryptops (originally "Otocryptops").Nonetheless, the detailed morphological features and figures provided in this work were unambiguously based on S. rubiginosus L. Koch, 1878 (referred as "Otocryptops ruliginosus" [sic]).Therefore, the name quadristriatus in the combination of Otocryptops sexspinosus quadristriatus in Takakuwa (1933a) did not satisfy the provision of Article 13.1 of the International Code of Zoological Nomenclature (hereinafter, Code; International Commission on Zoological Nomenclature 1999) and thus is unavailable.
In a synopsis of the Japanese centipedes, Takakuwa (1933b: 1459) provided a brief taxonomic account and morphological descriptions of the subspecies referred as "Otocryptops sexspinosus quadristriatus Verhoeff".However, Takakuwa considered that "O.s. quadristriatus" sensu Verhoeff was indistinguishable from the nominotypical subspecies "O.s. sexspinosus"; thus, he did not provide any description or definition that are purported to differentiate "O.s. quadristriatus" (see Article 13.1.1 of the Code).Therefore, we conclude that the species-group name quadristriatus in the combination of Otocryptops sexspinosus quadristriatus in Takakuwa (1933b) is also unavailable and the authorship of this nominal taxon is attributed to Verhoeff (1934), who established O. s. quadristriatus explicitly as a new subspecies.Moreover, according to Shinohara (1982Shinohara ( , 1990), Takakuwa's (1933b) description of this taxon was based on specimen(s) misidentified as "O.sexspinosus"; O. s. quadristriatus sensu Takakuwa (1933b) was later described as S. nipponicus Shinohara, 1990 (placed in synonymy with S. spinicaudus by Shelley 2002).
Remarks.Verhoeff (1934) established this taxon as a subspecies of the North American S. sexspinosus, based on brief taxonomic accounts.He only described the absence of tergal paramedian sutures, the presence of four longitudinal keels on tergites and the colouration of head and leg-bearing segments.Shinohara (1984) elevated quadristriatus to full species status, based on the following features: 1) cephalic marginal sulci reaching from postero-lateral margin of cephalic plate to antennae; 2) tergites without paramedian sutures and with four longitudinal keels; 3) arrangement of tibial and tarsal spurs on legs 19-23; and 4) a slightly slender "general form" compared with other species of the genus.It is unclear whether Shinohara compared quadristriatus with the North American O. sexspinosus sexspinosus or the Japanese "O.sexspinosus" (see above) and the characters of 1), 3) and 4) cannot conclusively distinguish quadristriatus from other species.Nonetheless, the presence of four longitudinal keels on tergites distinguishes S. quadristriatus from all other Scolopocryptops (except S. longisetosus sp.nov.; see below).The distinctness of S. quadristriatus is also supported by the molecular phylogenetic analyses (Fig. 13).
This species is absent from, but should be added to Chilobase 2.0 (Bonato et al. 2016).
Description of holotype [data from other specimens given in square brackets].Body length approx.31.4 mm [19.9-37.2mm] in 75% ethanol.Colour in life and in ethanol yellowish-brown with dark pigment on two basal antennal articles, purplish on subsequent articles; reddish-brown on forcipules; reddish-brown with dark pigment on lateral and posterior margins of cephalic plate, tergites 1, 22 and 23; brown with dark pigment on tergites 2-21; legs and ultimate legs brownish-yellow or orange with purplish dark pigment (Figs 8B, 10A, 11A).
Antennae 10.1 mm in length, approx.0.3× as long as body, composed of 17 articles; dorsal surface of two basal articles with sparse hairs and setae (sensu Bonato et al. (2010)) of various lengths, subsequent articles densely covered with long setae and minute short setae [in small specimens, most setae from article 3 shorter than those of two basal articles] (Fig. 9A); setae emerging from various-sized collars.Cephalic plate as long as wide; its surface sparsely punctate with minute hairs, with complete lateral margination (Figs 9B, 10A).
Second maxillae article 2 with elongated and semi-transparent dorsal spur distally; dorsal brush with transparent margin; pretarsus consisting of dark brown basal and semi-transparent short apical parts (Fig. 10C, D).Forcipular coxosternite and trochanteroprefemur sparsely punctate, coxosternite with transverse sutures on anterior third of coxosternite; trochanteroprefemur with small and blunt black process and basal suture; anterior margin of coxosternite strongly sclerotised and slightly convex, divided into two low lobes by median diastema (Fig. 10E).
Legs on anterior leg-bearing segments with sparse minute setae [setae denser in small individuals], posterior legs almost lacking setae [all legs setose in KUZ Z5123]; tarsi of legs 1-21 undivided; legs 1-19 with lateral and ventral tibial spurs and tarsal spur, legs 20 and 21, respectively, with tibial spur and tarsal spur; leg 22 without spurs.All legs with two accessory spines.
Etymology.The specific name is derived from the Latin compound adjective, "longus" (long) and "setosus" (hairy), referring to the long antennal setae of this new species.
Distribution.This species is known from Okinawa, Ishigaki and Yonaguni Islands in the Ryukyu Islands, Japan and is also widespread in Taiwan.Remarks.This species resembles S. quadristriatus, but S. longisetosus sp.nov.can be distinguished by the presence of long antennal setae (vs.setae short in S. quadristriatus; also see the Identification key provided in the Discussion).
The phylogenetic analyses indicate that specimens of this species from Taiwan have been misidentified as S. capillipedatus, based on the dense setae on ultimate legs (Chao andChang 2003, 2008;Chao 2008).However, S. longisetosus sp.nov.can be distinguished from S. capillipedatus by the presence of longitudinal keels and median depression on tergites.

Discussion
In the obtained phylogenetic trees, S. quadristriatus and S. longisetosus sp.nov.were strongly supported as monophyletic lineages.The analyses indicated that S. longisetosus sp.nov.comprises two lineages: Okinawa Island and the southern Ryukyus-Taiwan.These lineages differ in two external features, i.e. the presence/absence of dark pigment on the cephalic plate and the density of setae on ultimate legs.However, the pigmentation is subject to intraspecific variation in this genus and other scolopendromorph taxa and the density of the ultimate leg setae is also variable within Scolopocryptops species (e.g.Lewis (2003); Le et al. (2023)).It should be noted that the body lengths of the specimens from the southern Ryukyus and Taiwan (19.9-27.8mm) were generally smaller than those from Okinawa Island (23.4-37.2mm; juveniles excluded).Nonetheless, body length difference is not considered a taxonomic character here because it may be the result of different growth rates under different habitats (as speculated on Cryptops species; Lewis (2007)) or simply due to sampling bias.Additionally, because the COI genetic distances between the two lineages (5.77-8.87%)fell within the intraspecific divergence of Scolopocryptops (Garrick et al. 2018) and is smaller than the divergence amongst the sequences from the southern Ryukyus and Taiwan (4.89-9.17%),all the specimens from the Ryukyu Islands and Taiwan are considered a single species, S. longisetosus sp.nov.
It is noteworthy that four COI sequences of "S.capillipedatus" from Taiwan belonged to S. longisetosus sp.nov.(Suppl.material 3).Scolopocryptops capillipedatus, which is characterised by the dense setae on femur and subsequent articles of ultimate legs, was originally described from South Korea and has been recorded from Japan, Taiwan and Vietnam (Takakuwa 1938;Miyosi 1971;Chao andChang 2003, 2008;Chao 2008;Le et al. 2023).Chao (2008) provided a description of Taiwanese "S.capillipedatus" and noted that there were numerous long setae densely covering the femur, tibia and tarsi of the ultimate leg.However, this nominal species is clearly distinct from S. longisetosus sp.nov.because tergal keels are absent in S. capillipedatus (Takakuwa 1938(Takakuwa , 1940)).Although Chao (2008) did not mention the presence or absence of tergal keels, our specimens from Taiwan (KUZ Z5126 and Z5127) exhibited the characteristic longitudinal keels on tergites.The present result thus indicates that the records of "S.capillipedatus" from Taiwan were based on misidentified specimens of S. longisetosus sp.nov.Chao (2008) also described an unapparent median suture on tergites 1-3, which was not observed in our specimens, but described in Takakuwa's (1938) original description of S. capillipedatus.Morphological variability amongst Taiwanese populations needs to be examined, based on further taxon sampling.
Scolopocryptops longisetosus sp.nov. is quite similar to S. quadristriatus because they both have four longitudinal keels and median depression on tergites, as well as dark pigmentation on antennae and the dorsal surface of the body.Despite their phenotypic similarities, phylogenetic analyses did not support their sister relationship, but united S. longisetosus sp.nov.with three Japanese nominal species, S. ogawai, S. musashiensis and "S.nipponicus", which lack tergal keels (Fig. 13).The obtained phylogeny thus indicates that the longitudinal keels on tergites evolved in parallel within Scolopocryptops or that the presence of keels represents a

S. miersii
Asian/North American Scolopocryptops Neotropical/Afrotropical Scolopocryptops plesiomorphic character of the clade comprising these species.Within Scolopocryptops, the tergal keels and median depression are unique to these two species and S. hoanglieni Le, Schileyko & Nguyen, 2023, which bears "'drop-like' longitudinal median depression bordered by paramedian keels" (Le et al. 2023).However, the phylogenetic implication of the tergal keels remains uncertain because the phylogenetic position of S. hoanglieni is undetermined (Le et al. 2023).
It is also notable that all members of the ex-elegans lineage, except S. rubiginosus, lack complete paramedian sutures on tergites (Shinohara 1984(Shinohara , 1990;;Shelley 2002;Le et al. 2023), whereas all species of the elegans lineage and most of the Neotropical/Afrotropical species bear complete paramedian sutures (e.g.Chagas-Jr (2008); Chagas- Jr et al. (2023); Jonishi and Nakano (2023); Le et al. (2023)).Nonetheless, the evolutionary history of their paramedian sutures and the tergal keels remains unclear because the analyses failed to reconstruct a robust phylogeny of the ex-elegans lineage.Further systematic studies, for example, phylogenetic analyses using a larger taxon set including data from additional loci, need to be conducted to reveal the morphological evolution of Scolopocryptops species.
An identification key to Scolopocryptops species of East Asia Diagnostic characters and known localities mainly follow Le et al. (2023), but were updated, based on Jonishi and Nakano (2023) and the present study.
Antenna with sparse short hairs and setae on dorsal surface of two basal articles, subsequent articles densely covered with short setae.Cephalic plate with complete lateral marginal sulci.Tergites lacking paramedian sutures, tergites 6-20 with four longitudinal keels and median depression bordered by paramedian keels.