Chaerilus tricostatus Pocock, 1899

Chaerilus tricostatus Pocock, 1899 View in CoL

( Figures 36–43 View Figures 36–37 View Figures 38–43 , 212 View Figure 212 ; Tables 1–2) http://zoobank.org/urn:lsid:zoobank.org:act:4D9B559C-

2C6C-44C4-AF26-6227F8635F21

Chaerilus tricostatus View in CoL : Pocock, 1899: 266–267; Pocock, 1900: 54, 59–60; Henderson, 1913: 131–132; Kraepelin, 1913: 142, 146; Takashima, 1945: 100; Pérez, 1974: 31; Tikader & Bastawade, 1983: 318, 320–326; Bastawade, 1985: 260; Kovařík, 1998: 129; Fet, 2000: 327; Kovařík, 2000: 40, 57, 61–62, 70, 72; Bastawade, 2006: 450, 454; Di et al., 2009: 131–137; Di, 2009: 98, 106; Di & Zhu, 2009: 97; Sun, 2010: 101, 108; Kovařík, 2012: 3; Kovařík & Ojanguren-Affilastro, 2013: 132–133, 142; Di et al., 2013: 52 View Cited Treatment , 56, 88, 95; Di et al., 2014: 4–5, 9, 14; Yin et al., 2015: 42, 48, 50; Di et al., 2015: 111; Tang, 2022a: 55; Tang, 2022b: 3, 14; Tang, 2025: 16 View Cited Treatment .

TYPE MATERIAL ( Pocock, 1899: 267). India, Assam State, Tinsukia District , Sadiya Town (?in Khasi Hills), 2♂ , NHMUK.

OTHER MATERIAL. China, Tibet Autonomous Region, Nyingchi City, Mêdog County, Abor Hills , 28°07'58.2''N 95°07'26.7''E (approximated), 1♀ GoogleMaps , ZMNH ( Henderson, 1913: 131); Nyingchi City , Mêdog County, 29°20'N 95°20'E, 3♀, 4 juv. ♀ GoogleMaps , MWUH (Di et al., 2009: 133).

MATERIAL EXAMINED (VT). China, Tibet Autonomous Region, Nyingchi City , Mêdog County, June 2024, 1♀, purchased dried specimen, collector unknown ( Figs. 36–43 View Figures 36–37 View Figures 38–43 , 212 View Figure 212 ) .

DIAGNOSIS. TL ca. 48–52.1 mm for ♂ and 55.3–59.2 mm for ♀. General color dark blackish brown. Two pairs of lateral ocelli and one pair of median ocelli. Carapace and tergites granular, denser in females; CAM straight; sternite III – VI smooth, VII smooth to granular and tetracarinate. Metasoma I – V with carinae 10-8-8-8-7. Male telson not strongly elongated. PTC 5–6 in ♂ and 4–6 in ♀. VADC of cheliceral movable/fixed fingers 7–11/7–8. Pedipalp chela notably slender in ♂, ChL/W ca. 3.71 in ♂ and 2.21–2.43 in ♀; manus with D 1, D 4 – 5, and V 1 , 3 present and granular, E and I obsolete; D 3 highly obsolete an unridged dark stripe, indicated distally and proximally; DSC of movable finger 10–12, dorsal edge of movable finger straight .

CURRENT ASSESSMENT OF TAXONOMIC VALIDITY. Valid.

REMARKS. The Chinese population of C. tricostatus was first reported by Henderson (1913: 131) as an adult female from “Upper Rotung” in “Abor country” (a record cited by Kovařík (2000: 62)), which refers to the Abor Hills north of Rottung Village in Siang District. Again, this location is situated in the disputed territory (“ Arunachal Pradesh, India ” or “South Xizang, China ”). Di et al. (2009: 133) later provided the first illustrated description for a female C. tricostatus from Mêdog County, alongside information on 6 more females. In 2023, a friend of mine, Tongtong, collected another adult female from approximately the same location ( 29°19'20.6''N 95°19'48.4''E; iNaturalist, obs. ID = 196900793). Based on the map in Bastawade (2006: 450), the following additional localities are approximated ( Fig. 1 View Figure 1 ): Nyingchi City, Zayü County, 28°32'55.2''N 96°07'09.7''E; Shannan City, Tsona City, 27°18'16.4''N 92°32'36.4''E, 27°41'34.0''N 93°52'57.4''E. One record from iNaturalist (obs. ID = 117892140) was reported from Mêdog County ( 28°06'14.1''N 95°00'19.4''E), near the first reported Chinese female by Henderson (1913). The specimen was identified as a male C. tricostatus by me based on the rectangular and elongated manus as well as the absence of D 3 ( Pocock, 1899: 266).

As indicated by the species name, the dichotomous identification of C. tricostatus has been primarily relied upon the presence of only three “costate” carinae ( D 1, D 4, D 5) on the dorsal surface of its pedipalp chela (e. g., Tikader & Bastawade, 1983: 318; Kovařík, 2000: 70; Kovařík, 2012: 3; Kovařík & Ojanguren-Affilastro, 2013: 132; Di et al., 2013: 88; Di et al., 2014: 14). This species was described based on two males from by Pocock (1899: 266–267), who measured a TL of 48 mm for the holotype male, which increased to 50 mm and 52.25 mm in its redescriptions by Pocock (1900: 50) and Tikader & Bastawade (1983: 322) respectively. The type materials were said to be from “Sadi, in the Khasia Hills”, likely referred to the Khasi Hills in the Meghalaya State of India. However, Pocock (1900: 50) subsequently changed the locality to “ Sadiya , Assam ”. In a more detailed redescription by Tikader & Bastawade (1983: 326), they included both localities, selecting the second as its type locality (“… Sadiya (Type locality) Assam; Khasia hills, Meghalaya …”). Henderson (1913: 131) was the first to describe the female of this species based on 4 specimens from “Abor country”. He noticed a sexual dimorphism in ChL/W and carapacial granulation density, which was followed by Kovařík (2000: 62), and the dense granules in females were also concurred by Di et al. (2009: 133). The selected female for description measured 53 mm in TL ( Henderson, 1913: 132). The largest female was recorded with a TL of 59.2 mm in Di et al. ( op. cit.: tab. 1), who also documented the lowest known female ChL/W (13.7/6.2). All sternites were originally described as smooth except for the presence of 4 carinae on VII in Pocock (1899: 266), followed by Henderson (1913: 131), Kovařík (2000: 62), and Kovařík & Ojanguren-Affilastro (2013: 142). In the redescription of this species, Di et al. (2009: 136) described the sternite VII as “… with some small granules on posterior portion …” (note that this does not refer to the four granular carinae), suggesting an equivalent state of “weakly granular” or “subgranular”. However, Yin et al. (2015: tab. 3) simply described it as “granular” (logically, a larger set), while they also employed the more specific descriptor, “weakly granular”, for other congeners ( C. conchiformus and C. mainlingensis ).

Kovařík (2000: 62) provided a PTC range of 5–6 without specifying the sex, likely combined the male count (5–6) in Pocock (1899: 267; 1900: 60; however, Tikader & Bastawade (1983: 324) described the male holotype with 5/5 pectinal teeth) and the female count (5) in Henderson (1913: 132), whereas Di et al. (2009: tab. 1) further recorded one female pectine with a count of 4. Tikader & Bastawade (1983: 324) were the first to enumerate the cheliceral VAD in this species, providing a count of 8/7 for movable/fixed fingers of the holotype male. Later, Bastawade (2006: 454) reported a range of 8–9 and 7–8 VAD for the cheliceral movable and fixed fingers respectively. Di et al. (2009: 137) recorded a total range of 7–11 VAD on the movable finger for the 7 females they examined.

Pocock (1899: 267) initially mentioned 11 subrows of denticles on the movable finger of this species based on the holotype male, but then erroneously recorded it with 4 subrows in his redescription (Pocock, 1990: 60). Henderson (1913: 132) reported 10 subrows based on 4 new female specimens from “Abor country”. Kraepelin (1913: 142) subsequently keyed this species with as DSC of 10–11 (“… Schrägreihen des beweglichen Fingers 10–11 …”), but later in the same work ( op. cit.: 146) diagnosed it as “… die Zahl der Schrägreihen des beweglichen Fingers beträgt 11–12 …” (“the number of oblique rows of the movable finger is 11–12”). Tikader & Bastawade (1983: 324) did not directly provide the count, but illustrated a finger of the male holotype showing 11 subrows ( op. cit.: 916), if based on the division by larger granules. Kovařík (2000: 62) accepted the count of 11–12, which was later consistently adopted in Di et al. (2009: 133), Kovařík & Ojanguren-Affilastro (2013: 142), Di et al. (2013: 88), Di et al. (2014: 14), and Yin et al. (2015: tab. 3). The count of 10–11 was first followed by Bastawade (2006: 454) in his interspecific comparison of C. dibangvalleycus . In his dissertation, Di (2009: 98) keyed this species with a DSC of 10–12, but then ( op. cit.: 106) diagnosed it as 11–12 (as per Di et al. (2009: 133)), citing Bastawade’s description in the section of C. dibangvalleycus on page 101. The exactly same scenario is found in Sun’s (2010: 101, 103, 108) dissertation. In fact, the two dissertations are generally identical (and both listed C. mainlingensis as their new species).

Chaerilus tricostatus is one of the most unique Chinese Chaerilus species (alongside C. conchiformus and C. pictus ) for its relatively large size, essentially dark blackish color, and absence of D 3. The strongly sexually dimorphic pedipalp is also distinctive, with males showing long, cuboid chela. According to the diagnostic table summarized herein ( Table 1), the presence of 10–12 subrows of denticles on pedipalp movable finger would only associate it with C. pictus and C. tessellatus , whose distinctions have been discussed above. The lack of D 3 places it closer to C. dibangvalleycus and C. mainlingensis , from which it can be separated by its higher DSC ( vs. 7–8 in those two species). It is worth clarifying that D 3 is still observable in the moistened specimen with the aid of light from proper angles (pers. obs.; cf. Di et al., 2009: fig. 1). What gives rise to its apparent absence is but a significant reduction in the relative size of is constitutive granules ( Figs. 42–43 View Figures 38–43 ). However, the slightly concave intercarinal surfaces between D 1 and D 3, as well as D 3 and D 4, contribute to identifying the residual presence of D 3.

DISTRIBUTION. Nyingchi City (Mêdog and Zayü counties) and Shannan City (Tsona City).