Alacran chamuco Francke, 2009, new species

Alacran chamuco, new species

(Figs. 1–16, 18, 20)

Alacran sp.: Vignoli & Prendini, 2009: 4 (Fig. 1 A), 8 (Table 2), 35.

Type data. Holotype female, and only known specimen, from Te Cimutaa (NAD 27 777899 1987404) [N 17° 54’ 14.5” W 96° 22’ 37.6”, elev 944 m.], Municipio de Valle Nacional, Oaxaca, Mexico (Fig. 1); 25 April 2008, Paul Bryant; approximately 50 m. from the cave entrance. Deposited in the Colección Nacional de Arácnidos (CNAN T-0401), Instituto de Biología, UNAM. “Te” means “cave” in Chinanteco, the native language of the inhabitants of the Valle Nacional region.

Distribution. Known only from the holotype.

Etymology. The specific epithet is a noun in apposition, a name given in parts of Mexico (including the Chinanteca region) to the devil—which inhabits in the underworld.

Diagnosis. The most conspicuous differences between A. chamuco and A. tartarus are: (1) the former has five inner denticles on the fixed finger of the pedipalp chela, and six inner denticles on the movable finger, whereas the latter has six and seven inner denticles, respectively; (2) in A. chamuco the telson is proportionately smaller: the ratio telson length/carapace length in A. chamuco is 1.08, and in A. tartarus it is 1.25 (n=5, range 1.24–1.27) (16% shorter); the ratio telson width/carapace length in A. chamuco is 0.47, and in A. tartarus it is 0.58 (n=5, range 0.55–0.62) (23% narrower); and the ratio of telson depth/carapace length in A. chamuco is 0.43, and in A. tartarus it is 0.57 (n=5, range 0.55–0.62) (32% less deep).

Description. Based on holotype and only known specimen.

Color: Dorsum pale yellow-brown, venter and legs pale yellow; pedipalps orange-brown; granules on metasomal and pedipalpal carinae reddish brown.

Prosoma: Carapace subquadrangular, anterior margin straight; without distinct furrows or ridges; lacking median and lateral ocelli; with scattered, moderately dense small granulation (Fig. 2). Sternum longer than wide; with a shallow, broad posteromedian furrow (Fig. 3).

A. tartarus A. tartarus A. tartarus A. tartarus A. tartarus A. tartarus Standard A. chamuco Tel W / Car L 0.57 0.55 0.59 0.62 0.59 0.584 0.026076 0.47 Tel D/ Car L 0.55 0.55 0.56 0.62 0.55 0.566 0.030495 0.43

Mesosoma: Tergites I–VI smooth, lustrous, acarinate. Tergite VII with scattered, medium-sized granules posterolaterally; without distinct carinae; lateral margins finely serrate. Genital operculum obovate, with a complete median longitudinal membranous connection. Pectines each with three distinct marginal lamellae, five teeth and no fulcra; teeth finger-like, 3–4 times longer than wide, with sensory pegs on distal 1/3 to ¼ only (Fig. 4). Sternites III–VI smooth, lustrous, with few scattered macrosetae; stigmata small, round. Sternite VII with very few scattered granules, acarinate.

Metasoma: All segments longer than wide. I and II with three pairs of carinae each: Dorsolateral, ventrolateral and lateral supramedian keels moderately strong, granulose; III–V with two pairs of carinae each, dorsolateral and ventrolateral, all moderately strong, granulose. Intercarinal spaces smooth, lustrous. Telson globose, smooth, lustrous; aculeus short, strongly curved (Fig. 6), without lateral serrations.

Chelicera: Fixed finger with four teeth; basal and middle teeth not forming a bicusp. Movable finger dorsal margin with five teeth; ventral margin distinctly ridged, with distal tooth twice as long as dorsal counterpart. Both fingers densely covered with long, white hairs ventrally.

Pedipalp femur: Strongly compressed dorsoventrally, about 3–4 times wider than deep; with five distinct, granular carinae (prodorsal, proventral, retrodorsal, retromedian and retroventral), and with three trichobothria (Fig. 7). Dorsal face with few scattered granules; ventral face with very few granules basally.

Pedipalp patella: Subquadrangular in cross-section, slightly wider than deep. Four distinct, granular carinae: prodorsal, proventral, retrodorsal and retroventral. Anterior face smooth, lustrous. Dorsal face with three trichobothria, each surrounded by scattered granules (Fig. 8). Posterior face with 19–20 trichobothria (Figs. 9, 10), each surrounded by granules. Ventral face with sparse scattered granules; with three trichobothria along posterior margin.

Pedipalp chela: Digital carina with fairly distinct, single row of medium-sized granules. Dorsal secondary carina with somewhat scattered medium-sized granules. Dorsal marginal carina with widely scattered medium-sized granules. Retrolateral secondary carina present only on basal one-half, with somewhat scattered medium-sized granules. Proventral and retroventral carinae with somewhat scattered, medium-sized granules. Prodorsal and proventral carinae weak, with few scattered granules (Figs. 12, 14). Trichobothrial pattern as in A. tartarus. Fixed finger with six distinct rows of granules, with five outer and five inner denticles (Fig. 16). Movable finger with seven rows of granules, with six outer and six inner denticles (Fig. 18).

Legs. Long and slender (selected measurements in Table 1). Tibial spurs absent. Prolateral pedal spurs present on all legs. Retrolateral pedal spurs absent. Telotarsus without ventromedian spinules (Fig. 20); ungues long and curved.

Comparisons. A. chamuco differs from A. tartarus, the only other known species in the genus, as follows: (1) on A. tartarus the fixed finger of the pedipalps has seven rows of granules (Fig.17) instead of six (Fig. 16) clearly separated by six outer denticles instead of five; (2) the movable finger has seven inner denticles (Fig. 19) instead of six (Fig. 18); (3) the telson is considerably larger (Table 2; Figs. 5, 6); (4) the carinae on metasomal segment V are more finely granulose (Figs. 5, 6); (5) the pedipalp chela is rounder and the carinae are more granulose (Figs. 12–15).

Although both species posses enlarged vesicles, a phenomenon known in several other troglobitic scorpions (Volschenk & Prendini, 2008), in the new species it is not as large as in A. tartarus (Table 2). Considering the five adult females of A. tartarus (mean and standard deviation) and comparing them against the single A. chamuco available we find statistically highly significant differences between them: (a) for the ratio telson L/carapace L C = (1.25–1.08)/0.0122=13.93 (p<0.001); (b) for the ratio telson W/carapace L C = (0.584–0.47)/0.0261=4.37 (p<0.001); and (c) for the ratio telson D/carapace L C = (0.566–0.43)/0.0305=4.46 (p<0.001).

Biogeographical considerations. The caves in which the two species of Alacran have been found are only about 75 km apart on a straight line (Fig. 1). However, those on the Huautla Plateau are located at about 2000 m in elevation, whereas Te Cimutaa is at 944 m. Furthermore two deep canyons separate the Mazateca and the Chinateca regions: in a straight-line intersect from Huautla to Valle Nacional the contour first climbs to about 2300m; then, the canyon of the Rio Santo Domingo has an elevation of approximately 300 m; the contour raises again to 1500 m in elevation before dropping once more, at the Rio Perfume, down to 100 m in elevation; finally, is the climb to Te Cimutaa (topographical contour lines shown in Fig. 1). The probability that the two cave systems are interconnected beneath the Sierra Madre is infinitesimal.