Holotype 1 female specimen deposited at MZLQ, Brazil, Minas Gerais, Matozinhos, Cave 013, 19°31'57.21"S, 44°5'30.30"W Datum WGS84, col. Filho et al., setember.2016, manual collection. Paratype 1 male specimen deposited at MZLQ, same data as holotype; paratype 1 male specimen deposited at ISLA, same data as holotype; 1 female specimen deposited at ISLA, same data as holotype; paratypes 1 male specimen deposited at MZLQ, Brazil, Minas Gerais, Matozinhos, Cave 053, 19°31'47.92"S, 44°5'33.51"W Datum WGS84, col. Filho et al., setember.2016, manual collection; 1 female specimen deposited at MZLQ, Brazil, Minas Gerais, Matozinhos, Cave 053, 19°31'47.92"S, 44°5'33.51"W Datum WGS84, col. Filho et al., setember.2016, manual collection; paratype 1 female specimen deposited at ISLA, Brazil, Minas Gerais, Matozinhos, Cave 093, 19°31'56.06"S, 44°5'34.70"W Datum WGS84, col. Filho et al., setember.2016, manual collection; paratype 1 female specimen deposited at UFMG-AC, Brazil, Minas Gerais, Matozinhos, Cave 010, 19°31'58.45"S, 44°5'31.05"W Datum WGS84, col. Filho et al., setember.2016, manual collection.

Noun in apposition. The specific epithet “spelaion” is in honor of the Spelayon, a group of speleologists and for their contribution to the knowledge of Brazilian subterranean biology and geospeleology.

Neocarus species are often identified by a combination of characters, mainly using palp, pregenital and genital setae, while the ovipositor shape is usually considered a species-specific character. A summary of the characters used for species definition is presented in Table 1.

The definition of the species Neocarus spelaion sp. n. is given by; palp tarsus with 5 or 6 foliate setae (d-type); area between sternal and genital verrucae with two pairs of long, tapering setae; female with hairless pregenital area and 10-12 smooth genital setae, and ovipositor cylindrical, bare and with two terminal lobes. Male genital area with 7–11 setae, and pregenital area with 9–12 setae variable in shape, some of them smooth and pointed, or ribbed and pointed. Ovipositor with two terminal lobes and shape of setae on male pregenital and genital area are unique to N. spelaion sp. n.

Chelicera (Fig. 2A). Basal segment (170–212 µm) with 1 and fixed digit (237–267 µm) with 3 setae. Setae ch1”, ch2”, cht and ch2’ lightly barbed in some specimens (only visible at high magnification). Dorsal (id) and antiaxial lyrifissure (ia) well developed. Fixed digit with 1 tooth, movable digit (80–87 µm) with 1 tooth and a well-developed terminal hook. Movable digit with one ventral denticles in the basal portion. Internal surface of movable digit with an orifice of cheliceral gland (ocg). Sexual differentiation indistinct or absent.

Subcapitulum (Fig. 2B). All 4 pairs of paralabial setae present: pl1 small, conical; With’s organ (pl2) membranous and barbed marginally; rutella (pl3) with one distinct row of 5 teeth, inserted dorso-lateral; pl4 very small, inserted dorsal. With 4 circumbuccal (cb), and 8–9 median and subcapitular setae on male and 10–12 on female. Seta vm1 in all adults with rounded tip and robust, similar to circumbuccal setae. Females with one to three additional pairs of median setae with rounded tips (indicated by arrows in Fig. 2B, C). All setae in the median area of the subcapitulum in males show a fine, attenuated tip. Canals (ogl1 and ogl2) on lateral lips distinct.

Palp tarsus (Fig. 3A–B). Trochanter with 2–4 r and 2 p setae; Femur with 4–9 p, 6–16 r setae. Spike-like setae absent. Genu with 1–7 p, 16–29 r setae. Tibia with 16–30 s (some of these setae have small and fell barbs on base, and are positioned dorso-laterally), 16–27 r. Palp tarsus with lyrifissures iα and iπ. Setation includes two or one pointed and smooth setae positioned dorsally (probably v1), three s-type (smooth, resemble solenidia, but lack the transverse striation), 5–6 d-type (leaf-like), 3–4 v1-type, 3–5 v2-type, 14–18 ch-type and 7–8 sm-type setae. Pretarsus with well-developed claws. Total length of palp (trochanter/femur/genu/tibia/tarsus) 205–240 mm. No distinct sexual differentiation observed.

Idiosoma (Fig. 4A–B). Length 2100–2200; width 11600–12400, no significant diferences were observed among male and female. Color light with dark blue patches. Body sometimes with a brownish background resulting from ingested food. Dorsal shield with 130–172 ribbed setae and two pairs of eyes. One pair of lyrifissures present (same position and shape as observed by Klompen et al. 2015). Rostrum rounded. Dorsal portion of idiosoma between the shield and the preanal segment without setae, but with numerous lyrifissures arranged in transverse rows. Four stigma is present in separated body segments (VIII, IX, X and XI). Preanal segment with 1 dorsal and 2 lateroventral setae; anal plates in adults each with 10–12 stout, ribbed setae. Sexual differentiation indistinct or absent

Sternitogenital region (Figs 5–7). Sternapophyses with two setae, one small seta at the tip and one long and barbed seta positioned more basal. Sternal verrucae on adults with 2–5 barbed, tapering setae plus 1distinctly longer, barbed, tapering setae (St1). Remaining sternal area with 2 pairs of barbed, tapering setae (St2 and St3) on central area, and 4-6 pairs of long, ribbed setae, and commonly 3 pairs of lyrifissures, two pairs very large, the third smaller; all different in shape and size from “standard” opisthosomal lyrifissures. But some specimens have the central pair of lyrufissure duplicated (placed between St2 and St3) (Fig. 6A, B). Setae St2 and St3 equal in size. Pregenital capsules each with 1 long tapering seta (St5) and 4–5 ribbed setae. Pregenital and genital area in male with setae variable in shape, some of them smooth and pointed, or ribbed and pointed. Male genital area with 7–11 setae, and pregenital with 9–12 setae. In females, pregenital area nude and genital area with 10–12 smooth and pointed setae. The genital setae of the new species present a clear base but are hidden when the ovipositor is folded inside the body of the specimens. This group of the setae is considered genital and not eugenital, because eugenital setae are considered all setae present near or at tip of the ovipositor, without a clear base, like described by Vázquez and Klompen (2009).

Ovipositor when invaginated, consisting of a tube-like structure with two rounded and lateral lobs on tip, but when evagined these two lobs turn in a single structure, placed laterally to opening, without a eugenital setae. A single pair of gland-like structures in its median portion, and apex convex.

Legs (Figs 8–9). Leg I longer than others (leg I, 4310–4360 µm; leg II, 2135–2340 µm; leg III 2185–2375 µm; leg IV, 3295–3725 µm). Telotarsus I has a highly modified group of dorsal setae located in the apical portion, close to the tarsal claws, homologous to the Haller’s organ of ticks (Moraza 2005). All other leg segments carry three types of setae arranged in distal to basal lines: 1) tapering and barbed, 2) papilliform and 3) smooth seta.

Acrotarsus of leg II with a dorsal bifurcate seta and two smooth sensilla (one long and other ωa small) resembling solenidia (Figure 7). Acrotarsi of legs III–IV carry just 3 long, barbed and tapering setae dorsally. Additionally, acrotarsi II–IV carry 3 pairs of smooth ventral setae, 1 pair of lightly barbed ventrolateral setae (positioned distally), 1 pairs of smooth lateral setae and 1 pair of smooth laterodorsal setae (positioned distally). Basitarsi II–IV carrying coronidia dorsaly and two solenidia, ωd dorsodistal and partially sunk, and ωp basidorsal. Pretarsi in all instars with one pair of claws and 2 pairs of setae, one pair long and curved, and other smaller and apically pectinate. Pretarsal ambulacrum rounded and smooth.

The caves where the N. spelaion sp. n. was found receive large amounts of organic matter from the surrounding epigean system, which penetrates through skylights, gaps, cracks in the ceiling and at the main entrance. These caves contain a lot of loose rock, plus wide entrances, resulting in extensive photic zone in the hypogean environment, which enables the development of plant species in places near the entrance, providing a suitable place for shelter and permanence of Opilioacarida species (Fig. 10). However, it is believed that this species is not restricted to the cave environment and can be distributed in a much larger area than that studied, as found for other species of Brazilian Opilioacarida that inhabit caves and karst areas (Bernardi et al. 2012, Bernardi et al. 2013ab).

The transport of organic matter from the epigean to the hypogean environment can be an important factor for the opilioacarid species to establish a population in the interior of caves. There have already been reports that this species group feeds on pollen, fungi hyphae, plant fragments and arthropods (With 1904, van der Hammen 1966, Vázquez and Palacios-Vargas 1989, Walter and Proctor 1998, Klompen 2000). Analyses of the stomach contents of N. spelaion sp. n. specimens corroborated with these previous reports, revealing individuals had ingested plant tissue fragments, pollen, fungal spores, besides exuviae from invertebrates and mites (parts of Mesostigmata, Oribatida, Parasitengonina larvae and Alycidae specimen) (Fig. 11). The intact exuviae of mites (Acariformes: Oribatida) suggested that these individuals had been swallowed whole. As noted by Walter and Proctor (1998), fragments or even nearly complete bodies of other mites (Speleorchestes, Eupodidae, Teneriffiidae, Tarsonemidae and Oribatida) can be found in the fecal masses of Opilioacarida, but species in this group have never been observed preying on other organisms. Thus, it is likely that they scavenge the remains of dead mites and other invertebrates rather than actively predate these groups.

The Brazilian opilioacarids are widely distributed in karst regions, places where there is a great demand for mineral extraction. At least other 5 species, including a new genus, have been found in this formation, however, their descriptions have not yet been published (pers. observation).

The region of the Bambuí Geomorphological unit contains important limestone deposits and is under for intense pressure from mining activities, threatening caves and the surrounding epigean habitats (Ferreira et al. 2009, Simões et al. 2014). These activities threaten all species, due to the rapid and destructive nature of resource extraction methods, which often occur in an uncontrolled manner and which falls below the legally accepted standards.