Charinus giganteus, Souza & Ferreira, 2025

Souza, Priscila Emanuela De & Ferreira, Rodrigo Lopes, 2025, A small giant in the darkness: A new cave-dwelling Charinus (Amblypygi: Charontidae) from northeast Brazil, Zootaxa 5660 (2), pp. 228-242 : 231-238

Charinus giganteus sp. nov. ( Figs. 4–20 )

Type material. Holotype: ♀ (ISLA 126450). Lapa dos Brejões I cave (11°0'24.64"S 41°26'9.68"W), São Gabriel , Bahia, Brazil. leg. Ferreira, R.L. et al., 19.I.2024 . Paratypes: 1♀ ( ISLA 126451) , 1♂ ( ISLA 126452) , 1♂ ( ISLA 126453) , 1♀ ( ISLA 126454) , 1♂ ( ISLA 126455), unsexed juvenile ( ISLA 126456) , 1♀ ( ISLA 126457). Same data and local as holotype . 1♀ ( ISLA 126458) , 1♂ ( ISLA 126459) , 1♀ ( ISLA 126460). Same local as holotype. leg. Ferreira, R.L. et al., 13.IX.2024 . 1♀ ( ISLA 126461) , 1♀ ( ISLA 126462). Same local as holotype. leg. Ferreira, R.L. et al., 20.I.2024 .

Diagnosis. Charinus giganteus sp. nov. is distinguished by a unique combination of morphological traits: slightly projected carapace with a subtriangular frontal process and six rigid setae on the anterior margin; well-developed lateral and median eyes with a prominent median ocular tubercle; a tetrasegmented sternum with fully sclerotized plates. In females, the genital operculum is lighter in color with prominent posteromedial setae and sucker-shaped gonopods sclerotized at the base; in males, the operculum is rounded with scattered setae, and the fistula extends beyond its margin. Pedipalp femur with four dorsal and five ventral primary spines, consistently present across specimens, with setiferous tubercles on the first two dorsal spines; the patella has three dorsal (pd) and two ventral (pv) spines. Leg I bears 23 tibial and 41 tarsal articles. Leg IV has the basitibia divided into four pseudo-articles and the distitibia with 3 proximal and 15 distal trichobothria.

Comparative diagnosis. Charinus giganteus sp. nov. resembles C. santanensis , C. carioca , and C. euclidesi in the number of dorsal and ventral spines on the pedipalp femur, as well as the development of both median and lateral eyes. However, it differs markedly in the patellar spination: while the mentioned species have 6pd/3–4pv, 4pd/5pv, and 5pd/5pv respectively, C. giganteus sp. nov. has only 3pd/2pv. It also shares 7–9 denticles on the cheliceral claw with geographically close species from the Caatinga, such as C. diamantinus , C. mysticus , and C. santanensis . Yet, it can be distinguished by its reduced number of patellar spines and, in females, by the presence of basally sclerotized sucker-shaped gonopods, which are absent or weakly sclerotized in C. mysticus .

Charinus diamantinus differs from the new species by having 16 trichobothria on distitibia IV, compared to 15 in C. giganteus . When compared to Amazonian and northern species such as C. alagoanus , C. brescoviti , and C. magalhaesi , the new species exhibits more robust femoral spination and a greater number of basitarsal pseudosegments. Additionally, the sucker-like female gonopods in new species show lateral projections and a slightly convex posterior margin, resembling C. tocantinensis , C. renneri , and C. spelaeus , though differing in degree of sclerotization and shape.

Among the species from the Caatinga, all exhibit four pseudo-articles on the basitibia of leg IV and possess female gonopods with a sucker-like shape. In contrast, Amazonian species typically have two to three pseudo-articles on the basitibia of leg IV — with the exception of C. carvalhoi — and display female gonopods with a cushion-like morphology.

Description based on the female holotype and paratypes (♀ and ♂). (Measurements of the holotype and paratypes are provided in Table 1).

Coloration. Alcohol-preserved specimens: The prosoma is brownish-orange. The opisthosoma ranges from brownish-orange to light orange-yellow, with tergites and sternites moderate to light orange-yellow. The pedipalps and spines are dark reddish-orange, while the legs are moderate to dark orange-yellow. Live specimens: The prosoma displays a blend of light bluish-gray and pale blue. The opisthosoma is light yellow, with tergites appearing light grayish-yellowish-brown. The pedipalps and spines range from deep reddish-brown to black. The legs are centrally pale green, transitioning to light greenish-gray on the laterals.

Carapace ( Figs 4, 5 ). Carapace has a heart-shaped (cordiform) structure, slightly projected, with a length-towidth ratio of 7/10. Its surface is covered with scattered granules, more concentrated towards the anterior region. Posterior and lateral margins bear small setae, while the anterior margin is rounded, featuring three pairs of long, rigid setae alongside smaller setae at the base. Frontal process is large and subtriangular, with a slightly oval apex, and is only partially visible dorsally ( Fig. 5 ). It is 1.25× longer than wide. The lateral eyes are well-developed, with dark internal pigmentation that is either faint or absent. The median eyes are prominent, situated on a developed median ocular tubercle. A small seta is located posterior to each lateral ocular triad. Fovea is deep and triangular, positioned posteriorly. Median and transverse dorsosubmedian grooves extend from the ocular tubercle to the posterior margin. The anteromedian groove, unconnected to the fovea, stretches from the anterior margin to approximately 38% of the carapace length, while the posteromedian groove extends from the posterior margin to the fovea.

Sternum ( Fig. 6 ). The structure is tetra-segmented, with all plates fully sclerotized. Tritosternum is elongated, with a truncated apex projecting anteriorly beyond the base of the coxal pedipalp. It bears six pairs of setae: one apical pair, one median pair, and one basal pair of large setae, along with smaller setae at the base. The medial plate (tetrasternum) and the third plate (pentasternum) form a single convex structure with a rounded apex. This plate has a pair of large anterior setae and multiple smaller posterior setae. Tetrasternum is slightly larger than the pentasternum and features one or two medium-sized setae at its base. Metasternum forms a single subtriangular plate, with the anterior margin narrower than the posterior margin. It has four setae located in the membranous region.

Opisthosoma. Oblong in shape, longer than wide, with tergites exhibiting prominent punctation and sternites smooth ( Fig. 7 ).

Genitalia ( Figs 8–11 ). Female ( Figs 8, 9 ): The genital operculum is lighter in color than that of the male, with several setae along the margin and surface, and a pair of prominent setae located posteromedially. The gonopods are sucker-shaped, heavily sclerotized at the base, longer than wide, with a rounded opening and edges featuring a fold and a small posterior slit. The lateral margins are slightly projected. Male ( Figs 10, 11 ): The genital operculum has a rounded margin, wider than long, with few scattered setae, which are longer than those on the female margin. The base of the lateral lobes and the distal margin of the Fi are heavily sclerotized, with the Fi extending beyond the margin of the genital operculum. LaM has a slightly pointed projection located medially and ventrally to the Fi. LoD is drop-shaped, and LoL2 is irregularly oval, with the former being larger than the latter. Both are not visible ventrally, and the Pi is reduced. LoL1 is long, with a sclerotized base that gradually narrows towards LoL2.

Chelicera ( Figs. 15, 16 ). The basal segment has four internal teeth. The proximal tooth is the largest, with the two median teeth approximately half its size. The distal tooth is bifid, with the proximal cusp smaller than the distal one. Tooth length follows the order: IV> Ia> Ib> II> III. A small tooth is present on the retrolateral row of the basal segment, opposite the bifid tooth. The proventral and retroventral margins are densely covered with setae. The movable claw features 7–9 denticles.

Pedipalps ( Figs. 12–14 ). Trochanter: Features a ventral spiniform apophysis pointing forward, accompanied by a series of robust setiferous tubercles. On the prolateral surface, two spines of similar size are present: the first near the medial region and the second positioned above the apophysis projection, close to the femur. Four setiferous tubercles are aligned between the two spines, with two additional tubercles located proximally. Femur: The primary dorsal series consists of four (I> II> III> IV) or five spines, with setiferous tubercles along the first and second spines. In the holotype and some paratypes, a smaller spine is present between spines II and III. The femur also has five or six ventral spines, with an anterior setiferous tubercle aligned with the first spine (A1) (II> III> IV> A1> V). Additional smaller spines can be observed between spines II and III and spines III and IV in the holotype. Patella : Composed of three dorsal spines (I> II> III) and two ventral spines (I> II). A prominent setiferous tubercle is located distal to dorsal spine I, measuring approximately 3/10 of its length. Multiple smaller tubercles are distributed along the insertion margins of both dorsal and ventral spines. Tibia: Displays two dorsal medial spines, with the distal spine being about three times the size of the proximal one. A single ventral spine is present distally, accompanied by two setiferous tubercles near the anterior margin. Tarsus: Two to three dorsal spines are present, with the proximal spines being smaller. The proximal spine of the same series as the distal one measures about one-third the size of the distal spine. In larger specimens, up to four dorsal spines may be observed. Long setae are distributed along the anterior and distal margins. The cleaning organ is well-developed, featuring 24 setae in the ventral row. Apotele: Slightly curved.

Legs ( Figs. 17, 18 ). Leg I: Composed of 23 tibial articles and 41 tarsal articles. Leg IV: Features four pseudo-articles in the basitibia. The patella contains two trichobothria, while the basitibia has one or two trichobothria. The first pseudo-article of the basitibia has a trichobothrium positioned medially, and the last pseudo-article has a trichobothrium positioned proximally. The distitibia includes three trichobothria located proximally and 15 trichobothria distally. The trichobothrium bc is positioned slightly closer to sbf than to bf. The sc and sf series each contain six trichobothria. Additionally, the proximal portion of the distitibia features extra trichobothria. The tarsus consists of three pseudo-articles, with the first tarsal article exhibiting a distinct distal white ring.

Etymology. The specific epithet giganteus is derived from Latin, meaning ‘giant’ or ‘very large,’ and refers to the species’ notably large body size, with individuals exceeding 16 mm in length. This species is currently the largest known within the genus.

Habitat, threats and conservation status. Brejões Cave I spans 8,416 meters of mapped galleries, making it one of the most extensive cave systems in Brazil. Its striking main entrance, reaching nearly 100 meters in height, is considered one of the country’s most remarkable cave portals ( Fig. 2 ). The cave features two extensive, sub-parallel main galleries, characterized by their immense size, with some sections reaching up to 80 meters in height and 150 meters in width. These galleries are interconnected by expansive chambers with steep, uneven floors, as each conduit develops at varying topographic levels. The eastern gallery — the former course of the Jacaré River — is the widest and most prominent of the two conduits. It is distinguished by its regular, triangular-shaped sidewalls, reminiscent of the main entrance portal. This gallery contains substantial sedimentary deposits, including large piles of collapsed blocks, some of which are cemented or covered by carbonate concretions ( Berbert-Born & Karmann, 2002). Impressive speleothems are also scattered throughout this section, adding to the cave’s aesthetic and geological significance ( Fig. 3 ). In contrast, the second gallery, which runs parallel to the eastern one, is narrower and exhibits a predominantly polygonal cross-section. While it also features piles of collapsed blocks, these are smaller and consist of more flattened fragments compared to those in the main gallery ( Berbert-Born & Karmann, 2002). Despite its smaller size, this conduit contributes to the cave’s intricate geomorphology.

The Jacaré River, a key hydrological feature of the system, sinks approximately 300 meters before the main entrance of Brejões Cave I. It reemerges within the cave around 750 meters from the entrance and flows through the entirety of the westernmost gallery, the smaller of the two main galleries. The river disappears again near the cave’s second skylight, only to reappear within Brejões Cave II, where it resurfaces into the external environment near that cave’s main entrance. In addition to the river’s flow, Brejões Cave I also contains several stagnant water bodies scattered throughout the westernmost gallery. These pools are located in the cave’s lower areas, corresponding to its phreatic zone, further highlighting the dynamic and complex hydrology of the system.

Individuals of C. giganteus sp. nov. ( Figs. 19–20 ) were observed in a secondary gallery within the eastern gallery complex. Interestingly, while most parts of the cave remain relatively dry (except for areas near the Jacaré River) this particular conduit is noticeably more humid and slightly warmer than the rest of the cave. This contrast is likely due to the isolation of the chamber, which makes it one of the most stable microclimates within the system.

The dryness in most sections of the cave is influenced by strong air currents flowing through the expansive entrances at both ends of the main conduit. However, the gallery where the specimens were found is located at a higher topographic level and lacks direct openings to the surface. As a result, warmer and more humid air become “trapped” in this portion of the cave, creating favorable conditions for the observed species. Additionally, unlike much of the cave, this gallery is adorned with speleothems, contributing to its distinct environment. Collapsed blocks, which are common in wider chambers throughout the cave, are only sporadically present along this conduit, further enhancing its unique structure and ecological stability.

Individuals of C. giganteus sp. nov. were observed freely moving on the cave floor, particularly near bat guano deposits. These guano piles serve as the primary organic resource in the dry eastern galleries and attract a variety of scavenger invertebrates, such as crickets, isopods, and booklice, which likely constitute potential prey for the amblypygids. However, specimens were also observed in areas far from the guano piles, suggesting a high degree of mobility along this conduit.

The population appeared to be significantly large, with dozens of individuals recorded during two visits to the cave (rainy and dry seasons). Notably, no specimens were observed in other parts of the cave, indicating a strict habitat preference. Although the Jacaré River’s moist substrates appear to offer suitable habitat conditions, the persistent strong air currents presumably render this area unfavorable for the species. This suggests that C. giganteus sp. nov. selects more environmentally stable areas within the cave, prioritizing microhabitats with minimal wind and consistent microclimatic conditions.

Finally, the increasing anthropogenic threats to the cave’s unique ecosystem are deeply concerning. This cave has been used for religious purposes for centuries. During annual religious celebrations, thousands of visitors enter the cave, though most remain near the entrance, avoiding the deeper zones. However, occasional visitors venture further inside, as evidenced by graffiti found throughout the cave. Additionally, intense siltation during heavy rains poses a significant threat, as it can alter the cave’s substrates and disrupt the organic input to certain areas. Urgent measures, including regulated visitation and systematic monitoring, are essential to prevent the potential decline of these endemic species in the near future.

Figures

FIGURES 4–7. Charinus giganteus sp. nov. 4. Carapace (ISLA 126451). 5. Frontal process, dorsofrontal view (ISLA 126453). 6. Sternum (ISLA 126451). 7. Habitus (ISLA 126461). Scale bars: 0.5 mm.

FIGURES 8–11. Charinus giganteus sp. nov. 8. Female gonopods in dorsal view (ISLA 126462). 9. Female gonopods in posterior view (ISLA 126462). 10. Male gonopods in dorsal view (ISLA 126452). 11. Male gonopods in retrolateral view (ISLA 126452). Scale bars: 0.2 mm.

FIGURES 12–16. Charinus giganteus sp. nov. 12. Dorsal view of the right pedipalp (ISLA 126450). 13. Ventral view of the right pedipalp (ISLA 126450). 14. Frontal view of the tibia, tarsus, and claw of the right pedipalp (ISLA 126451). 15. Prolateral view of the right chelicera (ISLA 126460). 16. Prolateral view of the right chelicera (ISLA 126460).Scale bars: 0.1 mm (Figs. 14); 0.2 mm (Figs. 12, 13); 0.5 mm (Figs. 15, 16).

FIGURES 17–18. Charinus giganteus sp. nov. (ISLA 126460) 17. Trichobothria on the left distitibia IV. 18. Distal part of tibia I and proximal part of tarsus I. Scale bars: 0.1 mm (Figs. 17, 18).

FIGURES 19–20. Individuals of new species inside the cave.

FIGURES 1–3. 1. Karst in the north-central region of the São Francisco Craton (the Jacaré river is visible); 2. External environment of Brejões I cave; 3. Inner portion of cave.