Current challenges and preliminary morphological reassessment of the genus Chaerilus Simon, 1877 in China (Scorpiones: Chaerilidae) Author Tang, Victoria text Euscorpius 2025 406 1 89 journal article 10.5281/zenodo.16963598 1536-9307 16963598 3BDF2883-679A-4F3B-91E1-C2B896A79B67 Chaerilus wrzecionkoi Kovařík, 2012 ( Figures 5–10 , 68–75 ; Tables 1–2 ) http://zoobank.org/urn:lsid:zoobank.org:act:C097EF9A- B8A7-4BF1-A6BC-3E5416EF9B29 Chaerilus wrzecionkoi : Kovařík, 2012: 1–2, 11–13; Kovařík & Ojanguren-Affilastro, 2013: 132, 143; Di et al., 2013: 53 , 57–58, 88, 95; Di et al., 2014: 5 , 9, 14; Yin et al., 2015: 42–44 , 46, 48, 50; Di et al., 2015: 111 ; Tang, 2022a: 55 ; Tang, 2022b: 3 , 14; Tang, 2025: 16 . TYPE MATERIAL (Kovařík, 2012: 11). China , Tibet Autonomous Region , Nyingchi City , Bomê County , Tongmai Town , 30 km west of “Donjung”, 30°06'06.4''N 95°04'47.5''E (approximated), 2♂ 2♀ , FKCP . MATERIAL EXAMINED (VT) [putative; misidentified as C. tryznai in Tang (2024b)]. China , Tibet Autonomous Region , Nyingchi City , Bomê County , Tramog Town , Nyingchi City , Bomê County , 29°58'23.1''N 95°39'31.9''E , 3849 m . a. s. l., 22 nd July 2019 , 1♀ , leg. Tongtong ( Figs. 5–10 , 68–75 ) . DIAGNOSIS. TL ca. 33–37 mm for ♂ and 39–41 mm for ♀ . General color dark brown to blackish. Two pairs of lateral ocelli and one pair of median ocelli. Carapace and tergites granular; CAM straight; sternite III – VI smooth, VII granular and acarinate. Metasoma I – V with carinae 10-8-8-8-7. Male telson not strongly elongated. PTC 4–5 in ♂ and 3–4 in ♀ . Pedipalp chela slightly slender in ♂ , ChL/W ca. 2.57 in ♂ and 2.37 in ♀ ; manus with D 1 , D 3 – 5 , and V 1 , 3 present and granular, E and I obsolete; DSC of movable finger 8, dorsal edge of movable finger straight . CURRENT ASSESSMENT OF TAXONOMIC VALIDITY. Valid, but species characterization requires refinement. REMARKS. This species was rather tersely by two pairs of adults. Kovařík (2012: 11) diagnosed this species with a PTC of 3–5, but then detailed in his description with a note “… (females 3x4, 1x4; males 1x4, 3x5) …”. This could be a typographical error, where the first digits represent the number of pectines, aligning with the total pectine count for the four specimens . Therefore, the second digits likely represent the PTC, possibly indicating that one or three female pectines had 4 teeth, while the others had 3 teeth (according to the range in diagnosis). Yin et al. (2015 : tab. 3) considered the DSC of the male holotype to be 9, based on Kovařík (2012: fig. 64). The finger illustrated at a low resolution was covered with dirt, preventing a confident enumeration. I reckon at least 8 rows of denticles based on the inner denticles, concurring with Kovařík ( op. cit .: 11). Figures 54–59 . Adult female Chaerilus sp. ( cf. herta sp . n . ) from Mêdog (purchased), carapace (54), pectines (55), sternite VII (56), and right chela in dorsoexternal view (57) under white light, and left (58) and right (59) pedipalp movable fingers under UV light. Kovařík ( op. cit. : 13) briefly compared C. wrzecionkoi with C. mainlingensis and C. tryznai , which were the only resemblant Tibetan congeners at the time (now also C. pseudoconchiformus ). A single character was leveraged, the carinae on sternite VII, which are present in C. mainlingensis but absent in C. wrzecionkoi . However, a more reliable character appears to be D 3 , which is absent in C. mainlingensis but present in C. wrzecionkoi . The comparison between C. wrzecionkoi and C. tryznai was referenced to the dichotomous keys (No. 19, op. cit. : 2), in which males of C. tryznai possess proportionally narrower chela than C. wrzecionkoi (> 3 vs . <2.6). Based on Kovařík (2000 : tab. 1), females of C. tryznai also have narrower chela (2.91 vs . 2.37). Concerns may arise for the potential overlap when taking intraspecific variation and measurement inconsistency into account since the difference was based solely on one ratiometric. Although he examined multiple specimens of both species, no intraspecific variation was documented, which appears to be the author’s regular practice. While experienced authors may defend such a modus operandi , particularly when they can demonstrate having the species for comparison, readers cannot confidently accept their conclusions with a rigorous mindset. This approach leaves them hindered by doubtful diagnostic characters (e. g., ChL/W, as indicated in Figs. 7–10 ). The distinction between these two species are however conspicuous if one were to infer from the presumed adult female specimens examined herein (cf. Figs. 44–51 , 68–75 ). DISTRIBUTION. Known only from the type locality; Tongmai Town of Bomê County, in Nyingchi City. Morphological investigations into Chaerilus specimens collected from Drepung Nine adult females and 40 adult males ( Figs. 108–109 ) of an unidentified Chaerilus species (all had been preserved in 75% ethanol) were collected from Drepung Township, Mêdog County, the type locality of C. tessellatus . Congeneric species recorded in proximity also include C. tricostatus and C. tryznai ( Fig. 1 ). A cursory examination swiftly ruled out C. tricostatus as a potential match given the well-developed D 3 in all specimens. According to the summarized diagnostics ( Table 1 ), C. tessellatus and C. tryznai should ideally be differentiated by DSC , sternite VII, and metasoma II carinae, since males of C. tessellatus remain unknown. For the purpose of providing a general review of diagnostic traits previously used to differentiate Chinese Chaerilus species , the following characters were examined for the 40 Drepung males: PTC , DSC , ChL/W, CAM , sternite VII, and metasoma II– III carinae. The ventral accessory denticles ( VAD ) on the cheliceral fingers were not assessed, as the ridged segmental membrane in some specimens hindered manipulation of these structures, which appear to be either variable or nondiagnostic (interspecifically overlapped or with unknown intraspecific variation). Nevertheless, several other examined materials of Chaerilus are provided with photographs of VAD on their cheliceral movable fingers ( Figs. 92–107 ). It seems that the varying development degree of those denticles can obstruct unambiguous enumeration. The current analyses were founded upon two assumptions to eschew biases stemming from interspecific and ontogenetic variations: all males were (1) conspecific and (2) adult. Conspecificity was recognized upon observing no potentially meaningful morphological discrepancies apart from size and ChL/W (which will be further analyzed). Maturity was verified based on the coloration (uniformly dark brownish black, except for several evidently discolored specimens), carinae and granule development, and most importantly, the presence of hemispermatophores confirmed from several smallest males, ensuring the absence of any large juveniles that overlap with small adults in size. Given my utter lack of experience with this genus and the specimens’ long-term storage in ethanol that prevented perfect anatomy, identification on the hemispermatophores of small males was inferred from their similarity with the unambiguous hemispermatophores retrieved from the largest male ( Figs. 110–116 ). 1 . Methodologies (1) Carapace length as the primary proxy for total length and the secondary proxy for body size Conceptually, “size” is hereby defined as the volume an object occupies within physical space, representing a composite metric that incorporates length, width, and height. For scorpions, size theoretically refers to the total volume of all their segments, including minuscule structures such as setae. In contrast, “body size (BS)” exclusively pertains to the combined volume of the prosoma, mesosoma, metasoma, and telson, collectively denoted as the “body”. However, the visual impression of a scorpion’s size can be influenced by the relative size of its pedipalps or leg span. For instance, many hormurid species possess massive pedipalps in relation to their body size. Thus, BS is not necessarily an exhaustive representation of the scorpion’s overall size. “Total length (TL)”, or “total body length” as in Sissom et al. (1990: 217) , is the linear measurement along the longitudinal axis of the body (i.e., somatic axis). For practical purposes, TL is frequently used as the primary proxy for BS, as it represents the largest dimension (or “principal component”) contributing to the total volume of the scorpion body. The inclusion of chelicerae in body length measurements is predominantly observed in amateur scorpion-rearing circles and occasionally in academic studies (e. g., recently in Sanchez-Piñero et al. (2024: 190)). While excluding the telson is well justifiable, as this division is not regarded as a true body segment in scorpions ( Hjelle, 1990: 8 ; Lourenço, 2018: 4 ), chelicerae, being highly movable appendages, cannot reliably guarantee a standard or consistent measurement of body length. Moreover, the degree of cheliceral protrusion varies depending on the state of the specimen, both in vivo and in vitro . The derivation of scorpion TL varies among authors and/or depends on the specific research objectives. A crude, expedient method is to simply measure the linear distance between carapace anterior margin ( CAM ) and telson tip. The evident issue with this method is that the TL of specimens with an inflated or contracted mesosoma will be either overestimated or underestimated. A more meticulous way entails taking 14 independent segment measurements from carapace to telson, treating each cuticular component separately for mesosoma and metasoma. However, this method can inadvertently amplify the total error due to ambiguities in selecting the initial and terminal points for measurement on each sclerite, as well as the unavoidable imprecision inherent in manual operations. This error becomes evident during repeated measurements of the same specimen by the same practitioner. Suppose each measurement has an associated uncertainty (or variation, error) arising from measurement imprecision, denoted as δ, the total uncertainty in the sum (Δ) is given by: Figures 60–61 . Adult female Chaerilus sp. ( cf. herta sp . n . ) from Mêdog (purchased), dried specimen (now preserved in 75% ethanol), habitus in dorsal (60) and ventral (61) views, under white light; record not included in the map. where n is the number of measurements, and δ i is the uncertainty in the i -th measurement. Assuming all measurements share the same δ, the formula simplifies to Δ = (√14) ∙ δ ≈ 3.74 ∙ δ. To ensure there is no Δ between two independent measurements on the same specimen, one would need either to eliminate the individual δ entirely, or ensure that all δ cancel each other out. To control Δ under a given threshold k (in mm), each δ must be smaller than k / 3.74 mm (e. g., for k = 1, δ must be less than approximately 267 μm). Achieving this level of precision is highly challenging, if not practically impossible. Owing to the absence of a standardized protocol for accurate linear measurement, and the fact that some specimens exhibited contraction in the mesosoma, the carapace length (CaL) was used in this study as the proxy for TL to avoid cumulative uncertainties propagated through sequential measurements of individual body segments (measurement conducted manually with the aid of a digital caliper by carefully confining the anterior and posterior carapacial margins). Ergo, CaL represents the secondary proxy for BS. In the context of studying intersexual differences, Fox et al. (2015: 14) suggested that CaL itself may exhibit sexual dimorphism and thus be less reliable, recommending the use of metasoma I width (met1W) as the TL indicator. It is worth noting that the accuracy of width measurements may also vary depending on the species under study, particularly when the segment lacks nearly parallel bilateral surfaces. Given that the current objective focuses on a single sex and crude visual inspection revealed no significant somatic ratiometric discrepancies among individuals, CaL was chosen as the secondary—with TL being the primary—BS reference, as it is less flexible than carapace width, which is more prone to transverse deformation in preserved specimens, particularly among small species having less rigid cuticle (cf. Tang et al., 2023: fig. 91). However, for multispecies comparisons, CaL can be an unreliable proxy for either TL or BS due to the distinct morphologies (essentially the somatic ratiometrics) exhibited by different species, particularly when compared between sexes if significant sexual dimorphism is present. TL itself, being a one-dimensional linear variable, also does not effectively translate into size (or more precisely, volume), which is a three-dimensional variable. Predictably, few would contend that a 31 cm long cotton thread with a diameter of 2 mm is comparable in size to a 12-inch pizza or a cylindrical water bucket with a volume of 162 ×31π cm 3 . Overly simplified reduction leads to the significant loss of numerous crucial morphological (profile) information. A species may have a large TL, but this could essentially be the result of a disproportionately elongated metasoma, while the combined volume of its prosoma and mesosoma may be smaller than that of another species sharing the same TL, as the two species may differ in the relative width of mesosoma. For example, both adult female Androctonus gonneti Vachon, 1948 and adult male Lychas scutilus can reach ca. 85 mm in TL, yet the latter appears considerably smaller as a result of its overall slenderness; similarly, both adult male Androctonus turkiyensis Yağmur, 2021 and L. scutilus may have a CaL of ca. 6.6 mm , but the former reaches only 56 mm in TL (Tang, pers. obs.; see the figure gallery of this paper on ResearchGate). Their size discrepancy becomes even more pronounced in vivo when metasoma is curled over mesosoma. This is one of the many fundamental errors made by Forde et al. (2022) (e. g., failing to account for the different sources of LD 50 values and intraspecific variations in morphometrics, and neglecting to include many other non-medically significant species with smaller sizes and chelae, which would virtually nullify their result; it is also questionable regarding how they quantified the size of the chela), who argued that there is a negative correlation between scorpion “body size” and venom potency. In a multispecies context, TL, as a biased BS proxy, could potentially be corrected by a weighted average width ( W avg ). One may partition the scorpion body into two halves, with the upper half comprising prosoma and mesosoma, and the lower half being metasoma. Telson is excluded for convenience in this method, and the redefined TL is denoted as TL ’ . The weighted average width is hence given by: where L 1 is the upper length, L 2 is the lower length, Ŵ 1 is the estimated mean upper width, Ŵ 2 is the estimated mean lower width, W ca is the anterior width of carapace, W cp is the posterior width of carapace, W tm is the maximum width of tergite, W min is the minimum width of metasoma, and W max is the maximum width of metasoma. TL ’ can be normalized based on the width contribution. One way to correct the TL ’ for comparison is to use the ratio of weighted average widths: Figures 62–67 . Adult female Chaerilus sp. ( cf. herta sp . n . ) from Mêdog (purchased), carapace (62), pectines (63), sternite VII (64), and right chela in dorsoexternal view (65) under white light, and left (66) and right (67) pedipalp movable fingers under UV light. Figures 68–69 . Adult female Chaerilus cf. wrzecionkoi , 75% ethanol preserved specimen (same as in Figs. 5–10), habitus in dorsal (68) and ventral (69) views, under white light; record included in the map. where M is the metric (corrected TL ’ ) later used for multispecies comparison, and W avg,tot is the mean weighted averaged width of all species under comparison, which is calculated by dividing the sum of all W avg for each ( i -th) species by the number of species ( n ). This correction method implies that it is tailored for specific comparative contexts. Since proxies are utilized for their practical convenience at the expense of compromising precision or accuracy, authors may opt to derive TL ’ by directly measuring the linear distance from CAM to the lateral anal lobe of metasoma V. L 2 , attained from the more unstable metasomal segments, can also be obtained by simply subtracting L 1 from TL ’ . Additionally, to derive the mean upper width, individual measurements for the anterior and posterior widths of the carapace and each tergite may not be necessary. I propose to use only the anterior and posterior widths of the carapace and the maximum tergite width (e. g., width of tergites IV, V, or VI) for estimation. Similarly, for the mean lower width, it may be sufficient to measure the two metasoma with the minimum and maximum widths, after leveling the segment and applying a constraint rectangle to determine each value. Apparently, this simplified calculation would likely indicate its unsuitability in assessing species with prominently disproportionate metasomal segments (e. g., Apistobuthus Finnegan, 1932 , some Microbuthus Kraepelin, 1898 , and adult male Jaguajir pintoi (Mello-Leitão, 1932)) . Be that as it may, the final decision hinges on the practitioner’s judgement regarding the tradeoff between time investment and precision. Nevertheless, comparisons (in mm) between true mean metasoma widths ( W 2 , based on all segments) and min~maxaveraged metasoma widths ( Ŵ 2 ) suggested that even for species like Microbuthus spp. and adult male J. pintoi , the simplified calculation proposed herein would not lead to significant deviation from the true mean metasoma width: (1) M. gardneri Lowe, 2010 : W 2 2.106 ( vs. Ŵ 2 2.115) in holotype male and 2.342 ( vs. 2.335) in paratype female ( Lowe, 2010: 8–9 ); (2) M. kristensenorum Lowe, 2010 : W 2 2.146 ( vs. Ŵ 2 2.175) in holotype female and 1.316 ( vs. 1.325) in Wadi Shuwaymiyah female ( Lowe, 2010: 15 ); (3) J. pintoi : W 2 6.32– 7.54 ( vs. Ŵ 2 6.25–7.4) in two males and 5.94–6.76 ( vs. 5.9–6.7) in two females (Teruel & Tietz, 2008: tab. 1). However, such deviation was notably exaggerated in A. susanae Lourenço, 1998 , resulting in overestimations of the true mean metasoma width: W 2 6.622 ( vs. Ŵ 2 7.465) in Bostan male and 6.81 ( vs. 7.435) in Omidiyeh female (Navidpour & Lowe, 2009: tab. 2). The degree of amplification ( Λ = Ŵ 2 / W 2 ) is 0.98–1.01 for Microbuthus and J. pintoi , but approximately 1.1 (1.09–1.13) for Apistobuthus . The within-group difference is minimal at around 0.03 for { M. gardneri , M. kristensenorum , J. pintoi }, whereas this difference increases ca. 3- to 4-fold to 0.09– 0.12 when this group is compared against A. susanae . The Λ variation range for { M. gardneri , M. kristensenorum , J. pintoi } falls within the general variability (mean ± SD = 1.005 ± 0.019, n = 172) derived from several buthid species—as other families tend to exhibit even less variability in their metasomal segment widths (most possessing relatively slenderer metasoma)— that exhibit no conspicuously disproportionate metasomal segments: Aegaeobuthus gallianoi (Ythier, 2018) , Ananteris ochoai Botero-Trujillo & Flórez, 2011 , Anomalobuthus rickmersi Kraepelin, 1900 , Androctonus kunti Yağmur, 2023 , Androctonus sumericus Al-Khazali & Yağmur, 2023 , Barbaracurus exquisitus (Lowe, 2000) , Buthacus amitaii Cain et al., 2021 , Butheoloides nuer Kovařík, 2015 , Butheolus harrisoni Lowe, 2018 , Buthus castellano Teruel & Turiel, 2022 , Centruroides caribbeanus Teruel & Myers, 2017 , Chaneke hofereki Kovařík et al., 2016 , Charmus saradieli Kovařík et al., 2016 , Compsobuthus satpuraensis Waghe et al., 2022 , Gint banfasae Kovařík & Lowe, 2019 , Grosphus angulatus Lowe & Kovařík, 2022 , Heteroctenus turieli Teruel & Yong, 2023 , Hottentotta gibaensis Kovařík, 2015 , Ischnotelson peruassu Esposito et al., 2017 , Isometrus kovariki Sulakhe et al., 2020 , Janalychas granulatus Mirza, 2020 , Lanzatus huluul Kovařík & Lowe, 2021 , Leiurus macroctenus Lowe et al., 2014 , Lychas mucronatus (Fabricius, 1798) , Mesobuthus bogdoensis (Birula, 1896) , Microcharmusantongil Lourençoetal.,2019, Microtityus adriki Moreno-González et al., 2024 , Neobuthus amoudensis Kovařík et al., 2018 , Odontobuthus persicus Barahoei & Shahi, 2024 , Olivierus gorelovi (Fet et al., 2018) , Orthochiroides somalilandus Kovařík & Lowe, 2022 , Orthochirus fomichevi Kovařík et al., 2019 , Parabuthus robustus Kovařík et al., 2019 , Physoctonus debilis (C. L.Koch, 1840) , Pseudouroplectes jacki Lourenço, 2021 , Razianus farzanpayi Tahir et al., 2014 , Reddyanus jayarathnei Kovařík et al., 2016 , Rhopalurus ochoai Esposito et al., 2017 ( one female paratype metasoma IV width corrected to 4.9), Somalibuthus sabae Kovařík & Njoroge, 2021 , Somalicharmus whitmanae Kovařík, 1998 , Teruelius haeckeli Lowe & Kovařík, 2022 , Thaicharmus lowei Kovařík et al., 2007 , Tityobuthus mariejeanneae Lourenço et al., 2018 , Tityopsis rolandoi Kovarik et al., 2024 , Tityus ( Tityus ) achilles Laborieux, 2024 , Tityus ( Atreus ) moralensis Moreno-González et al., 2022 , Tityus ( Caribetityus ) schrammi Teruel & Santos, 2018 , Tityus ( Archaeotityus ) wachteli Kovařík et al., 2015 , Troglorhopalurus translucidus Lourenço et al., 2004 , Trypanothacus barnesi Lowe et al., 2019 , Uroplectes malawicus Prendini, 2015 , Xenobuthus xanthus Lowe, 2018 , and Zabius gaucho Acosta et al., 2008 (raw width data retrieved from their respective original or redescription papers, assuming no severe errors). It turned out that the investigated buthids generally tend to increase their metasoma width progressively in both directions, or show slight dilation at segment III or VI, facilitating quick visual determination of the two segments selected for calculating the estimated mean metasoma width in practice. It can also be noticed that some data provided by the authors were affected by manual imprecision based on their discordance with the illustrations, or the relatively high intraspecific fluctuations (maximum Λ difference ~0.08 seen in M. adriki , followed by 0.06 in T. translucidus ); achieving precision is important as a few authors often leverage ratiometric differences in metasoma for species delimitation. The overall fitness (Pearson’s r = 0.9996, RMSE = 0.048, MAE = 0.036; WSR p = 0.1006, effect size = 0.1245; nonnormal dataset ( p <0.0001), n = 180, including Microbuthus and Jaguajir ) supports Ŵ 2 as a relatively suitable estimator for true mean metasoma width. Figures 70–75 . Adult female Chaerilus cf. wrzecionkoi , carapace (70), pectines (71), sternite VII (72), and right chela in dorsoexternal view (73) under white light, and left (74) and right (75) pedipalp movable fingers under UV light. Figures 76–77 . Adult male Chaerilus variegatus , fresh specimen (now preserved in 75% ethanol), habitus in dorsal (76) and ventral (77) views, under white light. In extreme cases such as Apistobuthus spp. , a possible approach is to treat the enlarged segment (metasoma II) as a separate entity for calculation. This would entail dividing the lower half into segments II and {I, III, IV, V}, measuring the length of segment II (as only this measurement is required), and calculating their respective mean widths. Based on the empirical data (the same A. susanae data as before), this approach, albeit reducing overestimation to some extent, still led to deviations from the true mean metasoma width (true values: L 2 W 2 314.2 in male, 322 in female; basic estimation: L 2 Ŵ 2 354.2 in male, 351.5 in female; revised estimation: L 2 Ŵ 2 ’ 328.9 in male, 332.3 in female). An alternative correction involves applying an empirical scaling factor, k , to L 2 Ŵ 2 in the basic formula. This factor can be determined by the inverse of Λ , which equals 0.887 in the male and 0.916 in the female. Averaging these values gives k = 0.9. Multiplying L 2 Ŵ 2 by k results in 318.8 for male and 316.4 for female. Figures 78–83 . Adult male Chaerilus variegatus , carapace (78), pectines (79), sternite VII (80), and right chela in dorsoexternal view (81) under white light, and left (82) and right (83) pedipalp movable fingers under UV light. The above methodology does not factor in the variability in somatic depth across different species for two primary reasons: (1) the depth of the prosoma or mesosoma is highly flexible and influenced by the individual scorpion’s condition (e. g., states of gestation, starvation, and hydration); and (2) depth generally contributes less to the total volume of the scorpion, with the exception of certain dorsoventrally compressed and/or lithophilic crevice dwellers (e. g., genera Chiromachetes Pocock, 1899 , Hadogenes Kraepelin, 1894 , Hormurus Thorell, 1876 , Hormiops Fage, 1933 , Liocheles Sundevall, 1833 , Palaeocheloctonus Lourenço, 1996 , etc.). In the absence of other information, CaL or TL alone cannot be regarded reliable for representing the actual BS of a species of a random sex in a comparative context. Further studies are needed to assess how sensitive multispecies comparison results are to these biases and whether similar mathematical corrections can mitigate them. A more laborious approach would involve measuring all segments of the scorpion, followed by the use of dimension reduction algorithms (e. g., Principal Component Analysis) to obtain the first principal component, which captures the majority of the information contributing to BS. Alternatively, since metasoma tends to be more morphologically erratic within the order, the estimation of BS (under another definition) could be confined solely to the more conservative prosoma and mesosoma. In any case, a refined measurement protocol for each body segment is requisite before obtaining the raw values that are used to further calculate the TL or mean widths. Figures 84–85 . Adult female Chaerilus variegatus , fresh specimen (now preserved in 75% ethanol), habitus in dorsal (84) and ventral (85) views, under white light. When the present paper was in press, a meticulous study on various size predictive proxies for scorpions while taking phylogenetic relationships into account was published. Foerster (2025: 9) demonstrated that the length of metasoma V (met5L) was the best proxy for TL in buthids, followed closely by CaL (RMSE difference = 0.05; op. cit. : tab. 2). The general accuracy of using met5L as a TL predictor was confirmed for both sexes, also with no significant interaction with sex observed among other studied predictors ( op. cit. : fig. 3). The primary potential concern is the methodological discrepancy in measurements (as also acknowledged by the author; op. cit. : 4), since most morphometric data were sourced from past taxonomic studies by different authors. According to his diagram ( op. cit. : fig. 1), met5L was measured dorsally based on the visible anterior and posterior boundaries of the segment. While the posterior boundary may be consistently represented by the lateral lobe of the anal arch among authors (unless some pivoted to leverage the ventral boundary of the anal arch), the anterior boundary can vary depending on the specimen’s orientation, leading to different measurements. As discussed earlier, each metasomal segment has a base section that can be partially concealed within its anterior segment. The least biased point is likely the most proximal end (or anywhere near it that is located more proximally) of the median lateral carina for metasoma V (and the dorsolateral carina for I–IV). Although these technical considerations may seem overly fastidious, the potential measurement bias they introduce might have contributed to the slight difference in TL prediction accuracy between met5L and CaL. In practice, CaL is easier to measure given the clearer boundaries compared to the more irregular metasomal segments.