Tyrannochthonius aratu, Guimarães & Prado & Ferreira, 2025

Guimarães, Lucas, Prado, Guilherme C. & Ferreira, Rodrigo L., 2025, Two new species of Tyrannochthonius Chamberlin, 1929 (Pseudoscorpiones: Chthoniidae) from caves in Brazilian semiarid region., Zootaxa 5706 (3), pp. 367-382 : 374-378

Tyrannochthonius aratu sp. nov.

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Material Examined. Holotype male ( ISLA 126405), preserved in ethanol: Brazil , Iuiú , Bahia, Morro do Aurélio cave ( 14°30'49.34"S, 43°32'35.56"W), October 20, 2021, collected by Ferreira, R.L.

Etymology. The specific epithet aratu refers to the Aratu ceramic tradition, an archaeological complex associated with pre-colonial indigenous peoples from the interior regions of northeastern Brazil. The name honors the cultural history of the region where the species was discovered. This should be treated as a noun in apposition.

Diagnosis. Tyrannochthonius aratu sp. nov. most closely resembles T. rotundimanus in the following combination of characters: presence of two pairs of eyes, a small triangular smooth epistome, carapace chaetotaxy of 4+2: 4: 4: 2: 2, cheliceral dentition with 7 teeth on the movable finger and 10 teeth on the fixed finger, and coxal chaetotaxy of 3: 4: 5: 5. It differs from T. rotundimanus by more elongate pedipalp: femur 4.9 longer than wide (in T. rotundimanus 3.7–4.0), chela 5.0 longer than wide (in T. rotundimanus 4.5–4.7), femur/patella ratio 2.34 (in T. rotundimanus 1.94–2.01), fixed chelal finger with 30 teeth (in T. rotundimanus 18–22), fixed chelal finger with 9 intercalary microdenticles (in T. rotundimanus , 5); leg IV: tibia 4.8 longer than wide (in T. rotundimanus 2.9–3.1), telotarsus 11.0 longer than wide (in T. rotundimanus 6.0–7.6), basitarsus 3.0 longer than wide (in T. rotundimanus 2.2–1.8).

Description. Preserved specimen: Body slightly translucent light yellow; chelicerae and carapace slightly darker ( Figs 1B, D ). Live specimen: Carapace brown (charred orange); abdomen dark burnt orange; chelicerae reddishorange; pedipalps slightly translucent, with a color resembling aged copper ( Fig. 8D ). Vestitural setae simple, thin and sharp, anteriorly projected on prosoma and posteriorly projected on opisthosoma.

Carapace. Slightly constricted posteriorly, with a small difference between ocular width and posterior width of 0.07 mm. Surface smooth, without any furrows. Presence of two pairs of eyes, the anterodorsal ones without defined lens. Anterior margin smooth, epistome triangular, small and smooth, with 2 setae flanking the base. Carapace chaetotaxy: 4+2: 4: 4: 2: 2 (18), simple setae, the median lateral ones shorter ( Fig. 7B ).

Tergites. Undivided, smooth surface. Chaetotaxy uniseriate: I–XI 4: 4: 6: 4: 6: 6: 6: 6: 7(8): 4: 4.

Coxae. Palpal: Manducatory process with two acuminate distal setae, and 3 coxal setae arranged in a triangle. Pedal: Apex anterior of coxae I with an acute projection, coxae II with 6 coxal spines with branched apex (4–6 branches each), arranged in an oblique row ( Figs 7A, F ). Intercoxal tubercle absent. Coxal chaetotaxy: 3: 4: 5: 5 ( Fig. 7A ).

Male genital operculum. Genital opening slit-like; sternite II with 8 setae; sternite III with 7 marginal setae on each side (22 setae distributed throughout the sternite) ( Fig. 7G ).

Sternites. Chaetotaxy IV‒XI: 6: 6: 6: 8: 6: 6: 6: 8, anal operculum with 2 ventral setae.

Chelicerae. 0.15 times longer than wide. Hand with 5 setae, movable finger with 1 medial seta. Movable cheliceral finger with 10 teeth (1–2 acute, 3–5 worn and 8–10 vestigial teeth), galea absent; fixed cheliceral finger with 7 teeth (most distal one larger and the second most distal bicuspid, followed by 3 smaller and acute teeth), basal ones with rounded apex ( Fig. 7H ). External and internal serrula with 19 and 12–15 blades, respectively. Rallum with 6 unilaterally pinnate blades.

Pedipalp. Trochanter 1.71, femur 4.91, patella 1.7, chela 5.18, hand 1.90 times as long as wide; femur 2.34 times as long as patella; movable chelal finger 1.64 times as long as hand and 0.62 times as long as chela. Movable chelal finger with apodeme slightly sclerotized, with 31 well-spaced and acute teeth, except for the four most basal, which are vestigial, rounded, and contiguous; 3 intercalary microdenticles in the distal portion. Fixed chelal finger with 30 well-spaced and strongly acute teeth; 9 intercalary microdenticles in the distal portion. Trichobothria: ib and isb adjacent, located submedially on the dorsum of the hand. Trichobothrium esb is slightly distal to eb and slightly more distal to ist. In the posteromedial portion, it is slightly distal to est. In the distal portion, et is proximal to dx. On movable finger, sb is halfway between b and st; t is distal to b ( Fig. 7I ), b closer to t than sb (ratio distance sb–b / b–t = 3.0).

Leg I. Femur 1.77 times as long as patella, tarsus 2.27 times as long as tibia. Arolium undivided, slightly shorter than the simple claws. Chaetotaxy (trochanter to tibia) 0: 9: 8: 12 ( Fig. 7E ).

Leg IV. Femur and patella 2.91 times as long as wide, tibia 5.03 times as long as wide; basal tactile setae on both tarsal segments, basitarsus 2.95 times as long as wide, telotarsus 9.46 times as long as wide and 2.18 times as long as basitarsus. Arolium undivided, slightly shorter than the claws. Chaetotaxy (trochanter to basitarsus) 1: 3: 6: 10: 10 ( Fig. 7C ).

Measurements (mm): (length/width or depth in mm and ratios in parentheses calculated with three significant digits). Male holotype. Body length 1.17. Carapace 0.32/0.36 (0.88). Palps: trochanter 0.16/0.09 (1.7), femur 0.40/0.08 (5.0), patella 0.17/0.10 (1.7), chela 0.57/0.11 (5.18), movable finger length 0.35. Leg I: trochanter 0.11/0.08 (1.37), femur 0.23/0.05 (4.6), patella 0.13/0.05 (2.6), tibia 0.11/0.04 (2.75), tarsus 0.25/0.02 (12.5). Leg IV: trochanter 0.09/0.09 (1.0), femoropatella 0.41/0.17 (2.35), tibia 0.29/0.06 (4.8), basitarsus 0.13/0.04 (3.25), telotarsus 0.28/0.03 (9.3).

Ecological Remarks. The single specimen of Tyrannochthonius aratu sp. nov. was collected in Morro do Aurélio Cave, situated in the municipality of Iuiú, southwestern Bahia, Brazil. This cave develops within a relatively small limestone outcrop (approximately 2.2 km in length and 1.5 km in width), located about 2.5 km from the larger Serra de Iuiú massif. Morro do Aurélio Cave has a labyrinthine structure, which extends for 1,380 meters and features multiple entrances (primarily vertical shafts or skylights) located at the top of the outcrop. These features facilitate significant air circulation and light penetration, creating microclimatic conditions characterized by extensive dry zones, particularly during the rainy season when evaporation is intensified. Despite this overall dryness, T. aratu sp. nov. was found in a humid aphotic zone far from the cave entrances. The specimens were observed walking on moist sediment beneath limestone blocks in a chamber that receives episodic input of surface runoff during rainfall events. These inputs not only maintain localized humidity but also deposit allochthonous organic matter, such as plant debris, which likely supports the cave’s trophic network. The cave interior is remarkably well preserved, primarily due to the absence of regular human visitation. Archaeological artifacts (including lithic fragments and pottery shards) found within the cave attest to its historical use by ancient South American cultures. The vegetation atop the outcrop remains relatively intact; however, the surrounding external environment is heavily degraded. As in other areas of the Iuiú region, native vegetation has been largely replaced by pasturelands and monocultures. Nevertheless, due to its elevated position atop the outcrop, Morro do Aurélio Cave is likely to be less directly impacted by these external alterations.

Figures

FIGURE 1. Habitus. A) Tyrannochthonius iuiu sp. nov., dorsal view; B) Tyrannochthonius aratu sp. nov., dorsal view; C) T. iuiu sp. nov., ventral view; D) T. aratu sp. nov., ventral view. Scale bars: 1.0 mm.

FIGURE 7. Tyrannochthonius aratu sp. nov. Male holotype. A) Palp and pedal coxae, ventral view; B) Carapace, dorsal view; C) Right leg IV, antiaxial view; D) Left pedipalp, dorsal view; E) Right leg I, antiaxial view; F) Coxae II, detail of coxal spines; G) Genital area, ventral view; H) Right chelicera, dorsal view; I) Right chela showing trichobothrial pattern. Scale bars: (A–I) 0.1 mm.

FIGURE 8. Habitat of Tyrannochthonius aratu sp. nov. A) Outcrop where the Gruta Morro do Aurélio Cave is located (the yellow arrow indicates the main cave entrance); B) External landscape surrounding the cave; C) A conduit inside the cave; D) Holotype of T. aratu sp. nov., inside the cave.