Chaerilus assamensis Kraepelin, 1913

Tang, Victoria, 2025, Current challenges and preliminary morphological reassessment of the genus Chaerilus Simon, 1877 in China (Scorpiones: Chaerilidae), Euscorpius 406, pp. 1-89 : 10-11

Chaerilus assamensis Kraepelin, 1913

( Tables 1–2) http://zoobank.org/urn:lsid:zoobank.org:act:BEA6DB62-

1A10-4ADF-AA7A-24C758187ECB

Chaerilus assamensis : Kraepelin, 1913: 141, 144–145; Takashima, 1945: 101; Pérez, 1974: 31; Kovařík, 1998: 129; Fet, 2000: 324; Kovařík, 2000: 39–40, 42, 66, 69, 72; Di et al., 2009: 131–133; Di, 2009: 99; Di & Zhu, 2009: 97; Sun, 2010: 101–102; Kovařík, 2012: 2; Kovařík & Ojanguren-Affilastro, 2013: 131–133; Di et al., 2013: 52, 75; Di et al., 2014: 5; Tang, 2022a: 54; Tang, 2022b: 2, 3, 14; Tang, 2025: 16 .

Chaerilus dibangvalleycus : Bastawade, 2006: 451–454; Di et al., 2009: 131–133; Di, 2009: 98, 101–102; Sun, 2010: 101, 103–104; Kovařík & Ojanguren-Affilastro, 2013: 133; Di et al., 2013: 55 , 57, 88, 95; Di et al., 2014: 4, 9, 14; Yin et al., 2015: 42, 48–49; Di et al., 2015: 111; Tang, 2022b: 2, 14; Tang, 2025: 16.

=? Chaerilus dibangvalleycus Bastawade, 2006 (syn. Kovařík & Ojanguren-Affilastro, 2013: 133) http://zoobank.org/ urn:lsid:zoobank.org:act:10E079A1-B6B7-40CC-9AC7-6197BF3AF0B7 TYPE MATERIAL ( Bastawade, 2006: 454). China, Tibet Autonomous Region, Nyingchi City, Zayü County [“ India, Arunachal Pradesh State, Dibang Valley District, Mayodia or Mayudia”], 28°51'48.2''N 95°57'00.3''E (approximated), 6♂ 5♀, 2 juvs, NZSI.

TYPE MATERIAL (Kraepelin, 1913: 144). India, Assam State, 1♂, 1 juv. ♀, NZSI .

MATERIAL EXAMINED. None.

DIAGNOSIS. TL ca. 31.5–41.5 mm for ♂ and 36.75 mm for ♀. General color reddish to dark brownish; legs pale brown; telson reddish brown. Two pairs of lateral ocelli and one pair of median ocelli. Carapace and tergites granular, stronger in ♀; CAM arched (or weakly concave?) in ♂, straight in ♀; sternite III – VI smooth, VII granular and tetracarinate. Metasoma I– V with carinae 10-8-8-8-7. Male telson not strongly elongated. PTC 4–5 in both sexes. VADC of cheliceral movable/fixed fingers 4–5/8–10. Pedipalp chela slender in ♂ (?), ChL/W ca. 3.25 in ♂; manus with D 1, D 3 – 5, E, and V 1 , 3 present, smooth (?) to granular, I obsolete; D 3 mostly obsolete (?), indicated distally and proximally; DSC of movable finger 7–8 (?9), dorsal edge of movable finger straight .

CURRENT ASSESSMENT OF TAXONOMIC VALIDITY. Valid; but its synonymy with C. dibangvalleycus remains dubious.

REMARKS. Kraepelin (1913: 144–145) roughly characterized C. assamensis based on an adult male (31.5 mm, PTC 5/5) and a juvenile female (22 mm, PTC 4/4) from Assam, India. He noted that this species differs from all other congeners of the time by a distinctly arched (vs. straight) CAM in the male, which is flatter in the female (“… einen stärker gekrümmten Kreisbogen bildende Rundung des Stirnrandes …”; op. cit.: fig. 3a–b). All carinae on the pedipalp manus were described as developed and almost smooth, except for the “secondary inner keel” (= D 5; op. cit.: fig. 2) being somewhat granular (“… Handkiele alle entwickelt und alle fast glatt, nur der sekundäre Innenrandkiel etwas zackig körnig …”). This species has never been revised based on any materials since then. Another character later emphasized by Kovařík (2000: 42) was the presence of 7–8 subrows of denticles on the pedipalp chela movable finger (Kraepelin, 1913: “… Schrägreihen des beweglichen Scherenfingers (bezw. der äusseren Seitenkörnchen mit Einschluss des Endkörnchens) nur 7–8 …”, “… Beweglicher Finger mit sieben Schrägreihen …”), a count then observed only in C. tryznai from China (now known to occur in several other Chaerilus species).

Bastawade (2006: 451) described C. dibangvalleycus based on a number of adult specimens and two juveniles. Although the description was more detailed, several issues hinder a clear understanding of this species. Most importantly, he did not clarify the sex of the specimen illustrated. While the pectines showed 3 teeth (op. cit.: fig. 6), rendering it more likely a female, the presence of a pair of genital papillae (cited in the description) suggests it was a male. However, the author calculated 4 teeth for males and 5 for females. Moreover, he initially mentioned the presence of 4 and 8–9 ventral accessory denticles on cheliceral movable and fixed fingers (op. cit.: 451), but then shifted these counts to 5 and 10 in his interspecific comparison (op. cit.: 454). The illustration (op. cit.: fig. 4) showed 9 accessory denticles on the fixed cheliceral finger.

Kovařík (in Kovařík & Ojanguren-Affilastro, 2013: 133) synonymized C. dibangvalleycus with C. assamensis based primarily on geographic proximity and identical DSC, albeit examining no specimens. The current investigation further discovered that the descriptions of both species documented sexual dimorphism in the tergal granulation development, where it is weaker in males. Kovařík considered the carapace illustration in Bastawade (2006: 452, fig. 1) pertained to the female paratype, yet the original author did not explicate the sex in either description or figure caption. If one assumes that all depictions were of the male holotype (as that of the pectines), then the male C. dibangvalleycus clearly shows a weakly concave CAM. Another discrepancy between the two species lies in the metasomal carinae. Kraepelin (1913: 144) described the male C. assamensis as lacking inframedian (= median lateral) carinae (“ untere Mediankiele ”) on metasoma I–II. On the contrary, Bastawade (2006: 451) claimed that in C. dibangvalleycus , all carinae on metasoma I are well-developed, but the “laterals” on metasoma II–IV are not, suggesting a carina formula of 10-8-8-8 for metasoma I– VI. In addition, Kraepelin (1913: 144) briefly characterized the sternites of C. assamensis as matt and agranular (“… Bauchplatten matt, ungekrönt …”), contradicting the granular and carinate sternite VII described for C. dibangvalleycus , though it is unclear if Kraepelin’s qualification applies to all sternites. There was no indication from Kraepelin of a reduction in D 3 on the chela carinae, while the opposite appears to be the case in C. dibangvalleycus ( Bastawade, 2006: fig. 14). Kraepelin also did not provide enough metrics, but noted that the pedipalp finger was shorter than the manus in both sexes (“… F [inger].: H [inter] hand beim ♂ = 3,5: 5, beim ♀ 2,5: 3 …”) and a length to width ratio of manus for both sexes (“… Verhältnis von Länge der Hinterhand zur Handbreite beim ♂ = 5: 3, beim ♀ = 3: 2 …”). He described the chela as “rather narrow” (“… Hand ziemlich schmal …”) without specifying any difference between sexes, which could suggest either a weak sexual dimorphism (as also indicated by the manus ratio) or an ontogenetic variation (i.e., juvenile female had narrower manus than its adult counterpart). Bastawade, on the other hand, noted that male C. dibangvalleycus are more slender than females. This further suggest that his original figures were more likely depicted for the male holotype, where a narrow chela was illustrated. A crude measurement based on his figure 14 yields a ChL/W of 3.25.

In any case, the taxonomic status of both species is currently unclear. Given the morphological incongruence in some aspects between the two species, C. dibangvalleycus may in fact be a valid species. However, whether synonymous or not, the decision largely depends on the reliability of the characters discussed (i.e., whether they are intraspecifically stable in the two species): CAM, pedipalp and metasomal carinae, sternite, and ChL/W.

The earliest mentioning of C. assamensis as a member of the scorpiofauna of China appears to be in Di et al. (2009: 132–133), who cited Kraepelin (1913: 144) and Kovařík (2000: 42, tab. 2) in the bibliography under this species. This is baffling as neither work considered this species to be distributed in China or Arunachal Pradesh, since only two specimens of this species have been known for the whole time. Chaerilus dibangvalleycus was also included in their Chinese checklist, which was not synonymized with C. assamensis at that time. It is likely that the authors misread the table 2 in Kovařík (op. cit.: 72). This error perpetuated until Di et al. (2013: 52) and Di et al. (2014: 5) corrected it. Di et al. (2013: 55) considered the type locality of C. dibangvalleycus to be located in Mêdog County. According to the 2023 version administrative division map of Nyingchi City provided by the Department of Natural Resources of the Xizang Autonomous Region, the Dibang Valley District covers both Mêdog and Zayü counties. Approximated coordinates based on Bastawade (2006: map 1) place the type locality within Zayü ( Fig. 1 ), though rather near the border with Mêdog. It, however, would not be surprising that this species occurs in both counties. On iNaturalist, one observation record (obs. ID = 219229842) from Mêdog (28°50'12.0''N 95°52'25.9''E) featured an apparently young adult male Chaerilus species, close to the type locality of C. dibangvalleycus (ca. 8 km). The specimen matches Bastawade’s description for the coloration, as well as a narrow chela with obsolete D 3. A weakly concave CAM can also be observed from the fourth photograph. To secure the record, photographs are reproduced with permission in Figs. 2–4 . Another observation (obs. ID = 258985048) was recently uploaded for the same record (same date and coordinate).

Di et al. (2013: 57) also noted that “… Both sexes of C. conchiformus , C. dibangvalleycus and C. tryznai have anterior margin truncated, but only females of C. mainlingensis have same anterior margin of carapace as C. dibangvalleycus …”, which is bewildering. Only one sex (presumably male) of C. dibangvalleycus has been illustrated, which shows a weakly concave CAM, not “truncated” (= straight). Chaerilus mainlingensis is known only from females, and the original authors (with the senior author being Z.-Y. Di, who made the above statement) also described its CAM as “weakly concave” (Di & Zhu, 2009: 98). Therefore, while their second sentence holds true, it contradicts with the first where the CAM was regarded straight for C. dibangvalleycus . In their dichotomous keys, Yin et al. (2015: 49) characterized this species as “… carapace with anterior margin straight with a median notch …”, an eccentric description. A notch refers to an abrupt concavity seen in, for example, all Scorpiops species, which is not observable in Bastawade’s illustration. A straight margin with a median notch suggests the concavity is not gradual, but prominent. However, the original depiction shows a smooth inward curvature.

DISTRIBUTION. Known only from the type locality; Zayü County (“Mayodia”), in Nyingchi City.

Figures

Figure 1. Map showing the known distribution of Chinese Chaerilus species. Black lines represent China national border, downloaded from GitCode. Yellow lines represent county-level division in Nyingchi and Shannan cities, downloaded from Tianditu. Red dash lines represent disputed area (Arunachal Pradesh), downloaded from Natural Earth. The locality of C. pseudoconchiformus is represented by the examined adult pair. Localities of C. conchiformus include those of an examined specimen, iNaturalist observations, and published records (see text). Localities of other species include those of iNaturalist observations and published records only (see text). Insets: left above corner, closeup of type locality of C. herta sp. n.; right bottom corner, localities of the studied C. cf. tryznai (white cross) and C. cf. wrzecionkoi (white triangle).

Figures 2–6: Figures 2–4. Chaerilus cf. dibangvalleycus Bastawade, 2006, adult male in vivo habitus (photo courtesy ofAshwin Viswanathan); record not included in the map. Figures 5–6. Adult female Chaerilus cf. wrzecionkoi (same as in iNaturalist obs. ID = 108856746) preserved in 75 % ethanol for about 5 years, photographs taken under 365 mm UV light on A4 paper (5) and black cloth (6) in a dark room at night, on 5th November 2024 (the current author had already investigated problems associated with UV fluorescence using this specimen in 2023 deriving the same contrasting results, but no formal photos were taken). Setup and settings: Canon 5DsR paired with Kenko extension tubes (12 + 20 mm) and Sigma 70mm f2.8 macro lens; M mode, ISO 100, F 9.0, shutter speed 1/6 for Fig. 5 and 0’’6 for Fig. 6, single shot (not edited).