Genus Stenochrus Chamberlin, 1922

Type species: Stenochrus portoricensis Chamberlin, 1922 by original designation.

Stenochrus valdezi new species Figures 1–9; Table 1

Type material: MÉXICO: Chiapas: male holotype (CNAN-T0698) [18 June 2011, O. Francke, A. Valdez, C. Santibañez, J. Cruz, R. Monjaraz, G. Contreras, K. Zárate] from Cueva de San Francisco (16.09971ºN, 92.0469ºW, 1546 m), Municipio La Trinitaria. Paratypes: 4 females (CNAN-T0699), same data as holotype.

Etymology: The species name is dedicated to M. S. Alejandro Valdez-Mondragón for his help collecting the type series and for his contribution to the knowledge of arachnids from Mexico.

Diagnosis: Males can be distinguished by the rounded flagellum, with a conical posterior prominence and with two dorsal prominences which are rounded subdistally (Figs 1–3); by the palp trochanter with a distal conical projection (arrow in Fig. 6). Females can be distinguished by the spermathecae having conical lateral lobes, and the long and curved central lobes appearing like an upside down “J” (Fig. 8); and by the chitinized arch ending in pointed projections (arrow in Fig. 8).

Description. Male (Holotype): Body, palps, legs and flagellum pale brownish, chelicerae red brownish.

Prosoma: Propeltidium 1.20 long, 0.85 wide; anterior process distally rounded, with 3 apical setae, one behind the other two (2+1), and with 3 pairs of dorsal setae, the first larger than the other two in descending order. Without eyespots. Mesopeltidial plates 0.24 long, 0.06 wide; space length between the plates 0.25. Metapeltidium undivided, 0.30 long, 0.88 wide; metapeltidium plate very close to mesopeltidium. Anterior sternum triangular, with 10 setae. Posterior sternum triangular, with 6 setae.

Chelicera: Movable finger: Serrula with 21 teeth, guard tooth present (arrow in Fig. 4), with three small accessory teeth, Seta 1=3, 2=4, 3=4, 4=3, 5=7, 6=1. Fixed finger: with 7 smaller teeth between 2 primary teeth (Fig. 5).

Palps: Total length 3.33. Trochanter with a small mesal spur (arrow Fig. 7). Femur with 2 setae on the retrolateral margin, and 4 spiniform setae on the prolateral margin. Patella slightly curved posteriorly, with 3 pairs of ventrolateral setae (Fig. 6). Tibia with 8 plumose setae on the prolateral margin. Tarsus with 2 asymmetrical claws 0.2 long.

Legs: Leg 1, including coxa, total length 6.97, basitarsal-tarsal proportions 30: 5: 6: 6: 7: 6: 15. Femur IV 2.8 x longer than deep.

Opisthosoma: tergite I with 1 anterior pair of large setae and 3 pairs of small posterior setae; tergite II–VIII each with 1 pair of large dorsal setae; tergite IX with 1 pair of dorsolateral setae and 1 pair of lateral setae; tergite X–XI with 1 pair of lateral setae each side; tergite XII slightly telescoped, without evidence of posterodorsal process. Flagellum 0.54 long, 0.34 wide, 0.22 deep; with 4 large dorsal setae, 2 long setae in each bulb (Vl1 large and Dl1 small) and with 5 long ventral setae (Figs 1–3).

Female (Paratype): Similar to the male, differences: Body longer and more robust than male; palps longer but slightly thinner than male, and without spiniform setae. Leg I larger than male (measurements given in Table 1). Flagellum composed of 3 articles. Spermatheca with 4 lobes, median pair curved and larger than lateral pair. Lateral pair shorter and triangular in shape. Without bulbs or granules. Gonopod long and widened apically. Base of spermatheca with 2 sclerotized arcs (Fig. 8).

Variation. (Females, N= 4). Anterior carapaceal process of male with 3 setae, but females have 3 (2+1) or 2 (1+1) setae. Cheliceral movable finger of some females with 17 small teeth on serrula, accessory tooth with irregular shape, Seta 1=3, 2=3, 3=4, 4=11, 5=6, 6=1. Fixed finger of chelicerae with 4 smaller teeth between 2 primary teeth.

Characters Male Females

Holotype Paratype 1 Paratype 2 Paratype 3 Paratype 4 Remarks. Stenochrus valdezi resembles S. palaciosi (Reddell and Cokendolpher, 1986) (holotype examined), but they differ in size, S. valdezi is larger (4.35) than S. palaciosi (3.64). The shape of the flagellum is more globose and bigger in S. valdezi than in S. palaciosi (figs. 1–5, 11; Reddell and Cokendolpher, 1986). The spermatheca in S. valdezi has large median lobes and short lateral lobes, the median ones an inverted “J“ (Fig. 8). In S. palaciosi the median and lateral lobes have the same length (fig. 11; Reddell and Cokendolpher, 1986). The palps of S. palaciosi are more slender and smaller (2.18) than S. valdezi (3.33) (Fig. 6), the anterior margin of the trochanter ends in a conical projection as S. valdezi, however the trochanter of S. palaciosi is smaller (0.20) than S. valdezi (0.80) and armed with more spiniform setae. The patella is slightly larger in S. valdezi than S. palaciosi .

Distribution. Known only from the type locality (Fig. 9).

Natural history. The specimens were collected around 100 m inside a karstic cave, collected manually on the floor and walls. The habitat outside the cave is oak forest. The cave showed high degree of human disturbance, because there are religious ceremonies by the people that live in the town near the cave. Even inside the cave the subterranean river has been contaminated. The male holotype was found inside an old candle holder, and the females in a narrow passage with low concentration of oxygen.