Revision of the troglomorphic genus Troglostygnopsis Šilhavý, 1974 (Opiliones, Laniatores, Stygnopsidae)

In the present paper, we have made a taxonomic revision of the previously monotypic genus Troglostygnopsis Šilhavý, 1974. Based on the revision of diverse material, the genus is rediagnosed and the type species, Troglostygnopsis anophthalma Šilhavý, 1974 is redescribed. The new species Troglostygnopsis kalebi sp. nov. is described from specimens collected in a cave in Chiapas, Mexico, and this species is compared with T. anophthalma. A final discussion on some troglobitic genera of Stygnopsidae is addressed.


Introduction
As part of his revision of Mexican cavernicolous Laniatores, Šilhavý (1974) described the subfamily Troglostygnopsinae Šilhavý, 1974in Stygnopsidae Sørensen, 1932. According to Šilhavý, this subfamily differs from Stygnopsinae in having the fi rst distitarsus with more than two segments. In the same work, Šilhavý described the genus Troglostygnopsis Šilhavý, 1974 as the only member of Troglostygnopsinae. This genus was diagnosed as true troglobitic animals with ocularium reduced, eyeless, mesotergal areas unarmed, scutum with lateral projections between third and fourth areas, sometimes on posterior corners of scutum, chelicerae large, pedipalps long and armed with large spines, and distitarsi I and II with more than two segments. Šilhavý (1974) assigned two troglomorphic eyeless species to Troglostygnopsis: T. anophthalma Šilhavý, 1974 (type species) and T. inops (Goodnight & Goodnight, 1971), this last formerly assigned to Hoplobunus Banks, 1900. Later, Kury (2003 considered Troglostygnopsinae was proposed on troglomorphic autapomorphies; therefore, Kury and contemporaneous authors did not consider the subfamilial criterion of Šilhavý, keeping this subfamily as a junior synonym of Stygnopsinae (Reddell 1981;Kury & Cokendolpher 2000;Kury 2003;Mendes & Kury 2007).
During their taxonomic revision of selected stygnopsid genera, Cruz-López & Francke (2013b) noticed that male genitalia of Paramitraceras Pickard-Cambridge, 1905, Philora Goodnight & Goodnight, 1954 and Troglostygnopsis share similarities in the shape of the apical portion of penises and setal arrangement. In this regard, Cruz-López & Francke considered that these similarities could be due to common ancestry. Later, Cruz-López & Francke (2015) proposed a morphological-based phylogenetic hypothesis of the genus Karos Goodnight & Goodnight, 1944 and obtained two main results regarding Troglostygnopsis. First, this genus was recovered as polyphyletic, so they proposed the genus Mictlana Cruz-López & Francke, 2015 and transferred T. inops to it. Second, T. anophthalma together with Paramitraceras and Philora form a clade, supported by morphological characters of the male genitalia. In a broad sense, Cruz-López & Francke (2017) proposed a total evidence phylogeny of the family Stygnopsidae, including the largest number of taxa available to date. In that paper, two undetermined Troglostygnopsis were recovered as monophyletic, being the sister group of Sbordonia Šilhavý, 1977 in the subfamily Stygnopsinae, corroborating the monophyly of the genus.
Recently, Aguiñaga & Cruz-López (2019), Cruz-López et al. (2019) and Cruz-López & Francke (2020) have continued with the revisions of some genera of the family, especially those with troglomorphic traits. As a complement of the systematics of Stygnopsidae, here we present a taxonomic revision of Troglostygnopsis, rediagnosing the genus, redescribing T. anophthalma, and describing the new species Troglostygnopsis kalebi sp. nov., from caves in Chiapas, Mexico.

Material and methods
The material examined is deposited in the Colección Nacional de Arácnidos (CNAN), UNAM, Mexico and the American Museum of Natural History (AMNH), New York, USA. Color photographs were taken with an AxioCam Mrc5 camera attached to a Carl Zeiss V16 stereoscope. Drawings were made in Photoshop CS5 using assembled photographs to delineate the main structures. SEM photos were taken using a Hitachi S-2460N Scanning Electronic Microscope. Color photographs and SEM images were taken at the Instituto de Biología, as part of the Laboratorio Nacional de Biodiversidad (LaNaBio network) in the same institute. All images and schemes were edited using Photoshop. Nomenclature of the scutum shape is according to Kury & Medrano (2016). The relative size of chelicera with respect to the body, and the ratio between the length of scutum and the length of cheliceral hand was taken according to Cruz-López & Francke (2013a). Nomenclature of the main setiferous tubercles of pedipalpal tibia follows Acosta et al. (2007), with modifi cations for the family proposed in Aguiñaga & Cruz-López (2019). The macrosetal groups on the penis are named in accordance with Kury & Villarreal (2015), with modifi cations proposed by Cruz-López & Francke (2019b Kury, 2002Superfamily Gonyleptoidea Sundevall, 1833Family Stygnopsidae, Sørensen, 1932Subfamily Stygnopsinae Sørensen, 1932 Genus Troglostygnopsis Šilhavý, 1974Troglostygnopsis Šilhavý, 1974: 182. (type species: Troglostygnopsis anophthalma Šilhavý, 1974 original designation).

Emended diagnosis
Troglomorphic members of Stygnopsinae, eyeless, similar condition as Mexotroglinus Šilhavý, 1977, Toojah Cruz-López, in press, Chinquipellobunus madlae (Goodnight & Goodnight, 1967) (2013b): pars distalis tubular, with an apical depression where the follis arises, with many pairs of acute MS C on lateral sides, many pairs of spatulate MS A+B at the base and laterally on the pars distalis, two pairs of MS E, E1 small and in the middle of ventral side, E2 long and external to E1, and one or two pairs of MS D, near the base of follis. Troglostygnopsis can be differentiated from those genera with male genitalia with this pattern (Paramitraceras, Panzosus, Philora and Sbordonia) as follows: ocularium not pointing forward, pedipalps strongly armed with long spiniform setiferous tubercles, and males without glandular ventral tubercles on stigmatic area (in this last character similar to Sbordonia armigera Šilhavý, 1977).

Diagnosis
Movable fi nger of chelicera with three teeth (Fig. 1B), small and wide. Tubercles of leg IV small and scattered; patella with few, small tubercles (Fig. 2B). Penis with one pair of MS D, MS E1 below the level of E2 (Fig 3).

Preliminary considerations
The holotype was not examined; however, according to several caves studies and maps collected by the Association for Mexican Cave Studies (AMCS, information available at: http://www.mexicancaves.org/) we know that Grutas de Rancho Nuevo are the same as Grutas de San Cristobal; therefore, the male examined here is considered a topotype. This specimen is poorly preserved, without almost all legs, incomplete scutum and broken body. In the present work, we could only illustrate the chelicera, pedipalp, ornamentation of femur and patella IV, and male genitalia in detail. Fortunately, these structures are enough to recognize and diagnose this species. Additionally, Šilhavý (1974) made excellent drawings of dorsal and lateral view of the holotype, which are very clear and informative for taxonomic purposes. Finally, Šilhavý (1974), based on immature stages, mentioned two additional records for T. anophthalma from Cueva de la Golondrina and Cueva del Nacimiento del Río San Antonio, both in Bochil, Chiapas. Due to the specifi city in cave habitats in these species, it is necessary to collect adults from those caves to corroborate if they are conspecifi c with T. anophthalma or represent undescribed species.

Redescription
Male MEASUREMENTS. Scutum length: 4.9, scutum width: 4.1. CHELICERA (Fig. 1A-B). Scutum/cheliceral hand ratio: 1.37. Basichelicerite long, with diffuse bulla. Cheliceral hand slightly swollen, fi xed fi nger with six teeth distributed evenly throughout, middle one biggest; movable fi nger with three scattered teeth, basalmost and middle ones small and triangular, distal one diffuse. PEDIPALPS (Fig. 1C-D). Measurements: 2.30/1.00/1.75/1.80/1.00. Trochanter globose, with three ventral spiniform tubercles, apical one very large, dorsally with one spiniform tubercle. Femur slightly compressed laterally, with one ventral and one dorsal row of large spiniform tubercles pointing distally, these tubercles uniformly distributed throughout femur, ventral basalmost one most prominent. Patella with few small spiniform tubercles. Tibia with long armature, with relative sizes of three major tubercles (SST) on mesal side 1 = 3 > 2, and on ectal margin 3 = 2 > 1, on this segment two small setiferous tubercles between SST 1 and 2, and at apical end of the margin. Tarsus with six major tubercles on mesal side (2 > 4 = 5 > 6 > 1 = 3) and fi ve on ectal side (1 > 4 > 2 = 3 = 5). LEGS (Fig. 2). All segments very long and slender, femur IV longer than scutum. Ornamentation of femur IV composed of small and scattered tubercles forming longitudinal rows, patella covered with few small tubercles. PENIS (Fig. 3). Pars distalis with an apical concavity, lateral and apical margins softly rolled dorsally. Follis rugose, apices of dorsal bilobular projection long and pointed. One pair of small MS D lateral to base of follis, near to lateral margins of pars distalis. Four pairs of acute MS C forming two irregular rows on lateral sides. MS A+B formed by many spatulate setae, on latero-basal portion of pars distalis, some of them on ventral side. MS E composed of two pairs, MS E1 markedly below level of E2.

Female
Not examined.

Distribution
Known only from the type locality.

Diagnosis
Movable fi nger of chelicera with two teeth, low and wide (Fig. 5B). Tubercles of leg IV large and very close each other, patella with many of these tubercles (Fig. 6B). Penis with two pairs of MS D, MS E1 just above the level of E2.

Etymology
Patronymic honoring our colleague and friend Kaleb Zárate, an enthusiastic speleologist who has helped us collecting troglomorphic arachnids during several expeditions in southeastern Mexico.  BODY (Fig. 4). Scutum type zeta 'ζ', with both constrictions marked, specially C1, which marks the limits between prosoma and opisthosoma. Lateral margins of the scutum projected in lateral clear areas,   large and rounded. Entire dorsum smooth, with few small tubercles in middle of each mesotergal area. Ocularium at the frontal margin of the prosoma, acute, without eyes. CHELICERA (Fig. 5A-B). Scutum/cheliceral hand ratio: 1.29. Basichelicerite large and smooth, with few small tubercles on ventral and apical regions. Cheliceral hand slightly widened but not swollen. Fixed fi nger with four teeth distributed evenly throughout, central triangular-shaped. Movable fi nger with two teeth, one basal and one subterminal, basalmost rounded. PEDIPALPS (Fig. 5C-E). Measurements: 2.31/1.10/1.80/1.80/1.10. Trochanter globose, with long spiniform setiferous tubercles on ventral and dorsal faces. Femur compressed laterally, armed with dorsal and ventral row of about 10 very large spiniform setiferous tubercles. Additionally, femur with mesal apical spiniform tubercle, near patella. Patella covered with spiniform tubercles on dorsal and mesal faces. Tibia with large main armature, relative sizes of SST on mesal side 1 = 3 > 2, and on ectal margin 3 = 2 = 1. Also on tibia three very small tubercles between SST 1, SST 2 and SST 3 on mesal side, and four small ones between SST 1 and SST 2, one between SST2 and SST 3, and one apically. Tarsus with six major tubercles on mesal side (1 > 2 > 3 > 4 > 5 > 6) and six on ectal side (1 > 2 > 3 > 4 > 5). LEGS (Fig. 6). All segments long and slender, legs I-III without armature, ornate only with few disperse small tubercles. Ornamentation of femur IV formed by rounded and acuminate tubercles, which form longitudinal rows along entire femur, patella covered with many tubercles.  Šilhavý, 1974; red = T. kalebi sp. nov. Circles show distribution of Brujita Cruz-López, in press, Toojah Cruz-López, in press and the dubious record for Mictlana inops (Goodnight & Goodnight, 1971) reported by Goodnight & Goodnight (1973) (Goodnight & Goodnight, 1973); red = M. inops. PENIS (Fig. 7). Pars distalis wide, spoon-shaped. Follis multifolded, apices of dorsal bilobular projection acute, stylus arises from inside. Two pairs of MS D, lateral to base of follis, one pair very small and other formed by large acute MS. Five to six pairs of acute MS C forming curved rows on lateral sides. MS A+B formed by 16-17 spatulate setae, latero-basally to pars distalis. MS E composed of two pairs, MS E1 just above level of E2.

Female
Very similar to male, without remarkable sexual dimorphism.

Distribution
Known only from the type locality. Goodnight & Goodnight (1971, 1973, described and assigned six cave-dwelling harvestmen species to the genus Hoplobunus, based on their reductionist classifi cation scheme which they previously proposed in Goodnight & Goodnight (1953). Goodnight & Goodnight (1971) described Mictlana inops (as Hoplobunus inops) from Sotano de la Joya, in Tamaulipas State, northern Mexico (Fig. 8). This species was easily separated from other species of Hoplobunus by "general adaptation to a cave life", according to them. Subsequently, Goodnight & Goodnight (1973) reported some new records for M. inops; surprisingly, one of these is in Cueva del Nacimiento del Río San Antonio, Acatlán, Oaxaca State, southern Mexico, about 560 km south of those records near the type locality (Fig. 8). This record was supported by the Goodnights' conception of species highly being variable in morphology with very wide geographical distributions. Many years later, this record was corroborated as an undescribed troglomorphic species by Reddell (1981) and Kury (2003). Complementarily, the way that Goodnight & Goodnight delimited species has been refuted, especially for some Mexican harvestmen (e.g., Cruz-López & Francke 2015, 2019a.
The Northern portion of Oaxaca is characterized by the presence of numerous karstic caves, the most remarkable being the Huautla Cave System (HCS) (Steele & Smith 2019). In this area, seven troglomorphic stygnopsids have been reported, and remarkably, both species of Minisge inhabit HCS sympatrically but at different depths . Also, in this region of Oaxaca State, the locality of the false record of M. inops from Acatlán is about 66 km away from the type locality of Brujita chapulapa Cruz-López, in press, a troglomorphic species somewhat similar to Mictlana. A further revision of this specimen or additional specimens from the same locality would clarify its identity.
Additionally, the troglobitic genera Brujita, Mictlana (both in Karosinae), Toojah and Troglostygnopsis (both in Stygnopsinae) resemble each other externally very much, mainly by the presence of clear lateral projections in the middle scutum. This last character may perhaps have been the reason why Goodnight & Goodnight misidentifi ed the troglobitic stygnopsid from northern Oaxaca as M. inops. Cruz-López (in press) discussed the synapomorphies for both subfamilies, as well as other diagnostic characters used for the recognition of several taxa among the subfamilies. In this way, the shape of mesotergal sulci (sometimes only visible using an SEM), cheliceral dentition, cheliceral comb, armature of pedipalpal femur and patella, and arrangement of MS on the penis are enough for the recognition of all genera in the family.
Regarding Troglostygnopsis, both species are restricted to the central portion of Chiapas State, with both type localities separated by about 56 km. This genus, like the rest of the other troglobitic genera, shows a short-range endemic distribution (Fig. 8). Also, cheliceral dentition, pedipalpal armature, leg IV ornamentation, and male genitalia are more reliable characters than the tarsal count and presence of lateral clear areas, as Goodnight & Goodnight and Šilhavý have proposed. Also, based on the phylogenetic hypothesis of Stygnopsidae, lateral clear areas are homoplastic character (Cruz-López & Francke 2017). In conclusion, troglobitic genera with these structures show very restricted distribution ranges, Mictlana in northern Mexico, in the states of Tamaulipas and San Luis Potosí; Brujita and Toojah in northern Oaxaca, and Troglostygnopsis restricted to the central portion of Chiapas (Fig. 8).