Selachochthonius naledi, Prado 1 & Preez 2 & Ferreira 1, 2022

Prado 1, Guilherme C., Preez 2, Gerhard C. Du & Ferreira 1, Rodrigo L., 2022, Selachochthonius naledi sp. nov. (Pseudoscorpiones, Pseudotyrannochthoniidae), a new troglobitic species from South Africa, Subterranean Biology 42, pp. 125-138 : 125

Selachochthonius naledi sp. nov.

Material examined.

Holotype female (NCA 2021/1351), preserved in ethanol: South Africa, Cradle of Humankind (UNESCO WHS), Maquassi Hills Municipality, Villa Louisa cave (26°01'25.5"S, 27°42'43.0"E), 09 October 2019, leg. R.L Ferreira. Paratype male (NCA 2021/1352), Cradle of Humankind , Maquassi Hills Municipality, Yom Tov Cave (26°01'14.92"S, 27°42'53.46"E), 17 October 2019, leg. R.L Ferreira.

Etymology.

The epithet naledi refers to Homo naledi , an extinct hominid species discovered within the Dinaledi chamber. This chamber is located in the Rising Star Cave (Fig. 1C ), a World Heritage site located approximately 50 km from Johannesburg. The caves where the pseudoscorpions were found are located on the same hill as Rising Star Cave. The distances between the entrance of Rising Star Cave and the entrances of Vila Louise and Yom Tov caves are approximately 425 and 220 meters, respectively. Considering the fissure system associated with the carbonatic rock in the area, it is likely that the pseudoscorpions are able to disperse through small fissures to other macrocaves in the hill, including Rising Star Cave.

Diagnosis.

Selachochthonius naledi sp. nov. differs from other members of the genus by the following combination of characters: absence of eyes or eyespots ( S. heterodentatus Beier, 1995 with four well-developed eyes and S. serratidentatus Ellingsen, 1912 bearing four small eyes) ( Ellingsen 1912; Beier 1955); epistome triangular and strongly dentate ( S. cavernicola Lawrence, 1935 presents a flattened apex and slightly dentated epistome) ( Lawrence 1935); palpal femur with length of 0.65-0.66 mm or 6.2 times longer than wide (4.0 times in S. serratidentatus and S. heterodentatus with femur length of 1.0 mm); chela 6.1-6.2 times longer than wide (3.8 times in S. serratidentatus and 5.0 times in S. heterodentatus ) ( Ellingsen 1912; Beier 1955); fixed finger with 32-34 simple, sparse, acute and triangular teeth ( S. cavernicola with 23 sparse, simple and triangular teeth, presented in only 2/3 of the segment; S. heterodentatus with 28 acute teeth intercalated by 24 smaller teeth and S. serratidentatus with sparse, acute and complex teeth, each one intercalated by one or two smaller teeth) ( Ellingsen 1912; Lawrence 1935; Beier 1955); movable finger with 29-31 simple, sparse acute and triangular teeth ( S. cavernicola with 17 simple, sparse, acute and triangular teeth; S. heterodentatus with 16 acute and triangular, intercalated by 12 smaller teeth) ( Lawrence 1935; Beier 1955); presence of a small tubercle in both chelae between the 13th and 14th teeth of the female movable finger and between the 10th and 11th teeth of the male movable finger ( S. cavernicola , S. heterodentatus and S. serratidentatus lacks tubercle); 7-11 coxal spines tripinnate arranged in a single row on the anterior portion of the coxa I ( S. cavernicola with 12 bipinnate coxal spines) ( Lawrence 1935).

Description.

(Fig. 5E-F ). Body pale yellowish, mostly translucent; chelicerae slightly reddish orange, abdomen beige. Some parts of the body scaly. Vestitural setae sharp and anteriorly projected.

Carapace. (Fig. 2B-D ). Ratio length/width near 1.0, strongly constricted posteriorly showing a difference between ocular width and posterior width of 0.08-0.10 mm; anterior margin smooth; absence of eyes or eyespots; epistome strongly dentate and saw-like; posterior margin of carapace smooth; chaetotaxy 6: 4: 4: 2: 2 (18), lateral pre ocular setae are shorter in female (Fig. 2C ).

Chelicera. (Fig. 2A ). Hand with 7-8 setae; movable finger with 1 subdistal seta and fixed finger with 1 subdistal setae as well; galea absent; fixed finger with 11-12 acute teeth; movable finger with 8-9 acute teeth including one large distal tooth; rallum with 11 blades, middle blades long; serrula exterior with 22-25 blades, serrula interior with 19-21 blades.

Tergites. Not divided; surface smooth; chaetotaxy uniseriate, I-XI 2: 2: 4: 4: 4-6: 6-8: 6: 4-6: 4: 4: 4. Anal operculum with two dorsal setae. Pleural membrane smooth.

Coxae. (Fig. 3A-C ). Manducatory process with two apical setae (the distal one about half of the length of the proximal one); rest of palp coxae with 3 setae arranged in a triangle; delicate lamellae outlined by 15 small spines. Pedal coxae (Fig. 3A-C ): coxal spines tripinnate, with smooth tips arranged in a single oblique row in coxae I (7-11), chaetotaxy: I 4, II 4, III 4-5, IV 5 intercoxal tubercle present reduced between coxae III and IV, female bearing two setae and the male one.

Genital operculum of female: setae distributed in three horizontal rows: 2: 2: 3, genital opening not bifurcated (horizontally contiguous).

Genital operculum of male (Fig. 3D ): setae distributed in two horizontal rows: 2: 2; Anterior genital operculum with 10 setae; genital opening with 8-9 valvular genital setae.

Sternites. chaetotaxy IV-XI: 10-12: 12-14: 6-12: 6-8: 6: 6: 6: 4. Anal operculum with two ventral setae.

Palp (Fig. 4A-D ). Trochanter 1.4-1.8 times longer than wide, patella 2.3-2.4 times longer than wide, femur 6.2-6.6 times longer than wide. Femoral chaetotaxy 3: 4: 4-5: 2: 7: 1. Trichobothrial pattern: ib and isb located at the distal portion of the hand on a tiny hump (Fig. 4C-D ), adjacent to each other, eb proximad to esb, ist distad to esb (about the same distance between both), eb - esb - ist located at the base of fixed finger, it distad to est, et distad from it. Trichobothrium st located at third teeth level, sb proximad to b, t distad to b, b at the same distance from t and sb (Fig. 4C-D ). Fixed finger almost straight, movable finger slightly bent (Fig. 3A-D ). Chelal fixed finger with 32-34 acute, triangular, and widely spaced teeth. Movable finger with 29-31 acute teeth, growing from basal to distal, tubercle present between the 13th and 14th teeth of the female movable finger and between the 10th and 11th teeth of the male movable finger (Fig. 4C-D ).

Leg. IV (Fig. 2E ). Arolia same length as claws; a tiny protuberance near end of tarsus.

Measurements. (length/width or depth in mm; ratios in parenthesis calculated by using three significant digits): Female holotype and male paratype range. Body length 2.33 [1.86]. Carapace 0.55-0.70/0.52-0.70 (1.0). Palps: trochanter 0.21-0.35/0.15-0.20 (1.4-1.8), femur 0.93-1.22/0.14-0.20 (6.2-6.6), patella 0.38-0.51/0.16-0.21 (2.3-2.4), chela 1.39-1.8/0.30-0.23 (6.1-6.2), movable finger length 0.92-1.14. Leg I: trochanter 0.13-0.23/0.10-0.18 (1.3), femur 0.44-0.67/0.08-0.10 (5.9-6.8), patella 0.29-0.38/0.07-0.09 (4.1-4.4), femur/patella 1.5-1.8, tibia 0.23-0.35/0.05-0.07 (4.3-5.1), tarsus 0.54-0.65/0.05-0.06 (10.7-11.3). Leg IV: Trochanter: 0.24-0.27/0.13-0.17 (1.6-1.8), femur + patella 0.77-1.30/0.19-0.27 (4.1-4.8), tibia 0.50-0.68/0.10-0.12 (5.2-5.4), basitarsus 0.25-0.30/0.07-0.09 (3.4-3.6), telotarsus 0.55-0.73/0.05-0.06 (10.9-12.1).

Habitat and ecological remarks.

Despite extensive efforts in search of invertebrates in the caves, only two specimens of Selachochthonius naledi sp. nov. were found, thus indicating their low population density. In both Vila Louise and Yom Tov caves, the specimens were found in the deeper, moist and aphotic areas. The two individuals were collected from under block rocks in the cave floor. Neither specimens exhibited any phototactic behaviour. An interesting behaviour was observed for the individual from Vila Louise cave (female holotype): when gently touched by the brush bristles, the individual responded aggressively, repeatedly grasping the bristles. Even though one of the authors (RLF) has been collecting cave pseudoscorpions for the last 30 years (especially Chthonioidea), this “aggressive” behaviour has never been recorded by him before. Potential prey in both caves include springtails, juvenile crickets and isopods ( Styloniscidae ).

Figures

Figure 1. Distribution map of Selachochthonius species in South Africa A Africa continent, detail on South Africa country B South Africa, exhibiting distribution of Selachochthonius species with detail on S. naledi sp. nov. type localities C Selachochthonius naledi sp. nov. distribution area, exhibiting Yom Tov, Villa Louise and Rising Star Caves (Homo naledi type locality), detail on quarry activity occurring nearby.

Figure 2. Selachochthonius naledi sp. nov. A left chelicera of female holotype, antiaxial view B female holotype carapace, showing chaetotaxy of carapace C detailed anterior margin of female paratype carapace D detailed anterior margin of male paratype carapace E leg IV of female holotype, showing tubercle location. Scale bars: 0.25 mm (A, C-D); 0.5 mm (B, E).

Figure 3. Selachochthonius naledi sp. nov. A female holotype palp and pedal coxae B detail of female holotype coxa I C detail of female holotype coxal spines D leg I of female holotype E male paratype genitalia, showing arrangement of setae F right pedipalp of female holotype, dorsal view. Scale bars: 0.3 mm (A); 0.1 mm (B-C); 0.5 mm (D); 0.05 mm (E); 1.0 mm (F).

Figure 4. Selachochthonius naledi sp. nov., female holotype A right pedipalp chela, showing lyrifissures and trichobothrial pattern, dorsal view B right pedipalp chela, showing lyrifissures arrangement, ventral view C left pedipalp chela, showing teeth morphology, trichobothrial pattern and tubercle location, antiaxial view D right pedipalp chela, antiaxial view. See Material and methods for abbreviations. Scale bar: 1.0 mm.

Figure 5. Type locality and habitat of Selachochthonius naledi sp. nov. A Villa Louise cave entrance B Villa Louise cave interior general aspect C Villa Louise cave interior, showing altered floor D Yom Tov cave entrance E live female holotype F live male paratype.