Leiobunum silum Shultz 2018, sp. nov.
Creators: name: Shultz, Jeffrey W.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Opiliones
Phalangiidae
Leiobunum
Leiobunum silum

description: Leiobunum silum sp. nov.
Figs. 1–13
Type material. holotype ♂ (selected for relative completeness of legs), allotype ♀ (selected for relative completeness of legs), other paratypes 6 ♂, 2♀. U.S.A.: Arizona: Cochise County: Chiricahua Mountains, Coronado National Forest, " Rustler's Camp " [= Rustler Park Campground?], (31.9055° N, 109.279° W), elev. 8500’ [2591 m], 9 Sept. 1950, W.J. Gertsch. Deposited in the American Museum of Natural History.
Etymology. Silum is the neuter form of the Latin word silus, meaning snub-nosed or pug-nosed. The name refers to the up-turned anterior margin of the carapace in both sexes (Fig. 11).
Diagnosis. Submarginal pro- and retrolateral rows of denticles entirely absent on pedal coxae (Figs. 2, 3, 5, 6), as in Nelima. Terminus of male labrum inflated to arrowhead shaped, armed with many minute denticles (Fig. 12). Median anterior margin of carapace reflected upward revealing an anterior transverse crescent-like plate, often bulging medially (Fig. 11). Significant sexual dimorphism in dorsal cuticle: Male carapace finely crenulate; scutum parvum and first two free tergites covered in low, rounded tubercles; dorsum primarily very dark brown to nearly black, median longitudinal mark subobsolete anteriorly, obsolete posteriorly (Fig. 1). Female dorsum granulate throughout, lacking crenulation and tubercles of male (some tubercles may occur on anterior scutal tergites); median longitudinal mark distinct on scutal tergite 1 but becoming increasingly indistinct posteriad, bordered laterad by light spots and splotches (Fig. 3). No similar combination of features is known from other Leiobunum species in the southwestern United States.
Description of male. Measurements of male holotype (in mm). Body length, 3.4, carapace length, 1.2., carapace width, 2.2. Palp: femur, 1.2; patella, 0.6; tibia, 2.1; tarsus, 1.4. Legs (femur, patella, tibia, basitarsus, telotarsus): I: 7.4, 1.4, 6.0, 8.2, 10.9; II: 11.4, 1.7, 10.1, 11.8, 21.3; III: 7.3, 1.4, 6.0, 9.0, 11.8; IV: 10.0, 1.6, 7.8, 12.3, 15.1.
Dorsum. Carapace finely granulate marginally, coarsely granulate medially, regions laterad and posteriad to ocularium finely crenulate; crenulations arranged in longitudinal crests and valleys at posterior margins of meso- and metapeltidia. Scutum and first two free tergites covered in low rounded tubercles. Last tergite and anal operculum finely granulate. Dorsal surface otherwise unarmed except for scattered erect setae. Ocularium smooth; weakly canaliculate anteriorly, becoming deeply canaliculate posteriorly; carinae unarmed except for scattered erect setae; anterior surface sloping steeply upward, posterior surface bulging posteriorly over post-ocularial carapace, base constricted posteriorly (Figs. 1, 3). Anteromedial margin of carapace without distinct doublure, forming vertical bulging crescent above supracheliceral lamina (Fig. 12). Supracheliceral lamina formed by two large, anteriorly projecting arched plates meeting at median sulcus; anteromedial margins with short, blunt, unarmed anterior projections. Ozophores prominent, surrounded with finely granulate cuticle, ozopores directed anterolaterally.
Venter (Fig. 2). Labrum (Figs. 2, 12) relatively long, projecting anteriad between flexed chelicerae; shaft thick, swollen subterminally then tapering to blunt point, sometimes forming robust arrowhead; with scattered fine, dark denticles, density and size of denticles greatest on lateral surfaces of bulging region. Genital operculum finely granulate, unarmed except for scattered erect setae. Sternites finely granulate, unarmed except for setae, most setae arranged in imperfect transverse row on each sternite.
Chelicera (Figs. 2, 3, 12): Basal article with short, prodorsal, longitudinal row of setae with row curving medially near distal margin; second article with prolateral (medial) row of setae increasing in density and length distally, several long setae on anterior surface at base of fixed finger.
Palps (Figs.1–3, 9–10): Trochanter simple, without apophyses, prolateral surface with marginal row of erect setae, retrolateral surface glabrous. Femur with broad dorsal and ventral fields of erect setae, densest on distodorsal surface; pro- and retrolateral surfaces largely glabrous; proximal retrolateral to ventral surfaces with field of denticles extending almost to midway of femur on retrolateral surface, femur otherwise unarmed. Patella and tibia unarmed except for scattered erect macrosetae, prolateral patellar apophysis absent; tibia with a few recumbent microsetae on retrodorsal surface. Tarsus as long as tibia + patella, coated with erect macrosetae (with ventral tuft near tip) and recumbent microsetae; long proventral row of ~26 sharp denticles, denticles spaced by a distance slightly greater than denticle thickness. Claw pectinate, with three or four small proximal teeth, or essentially smooth.
Legs. Coxae (Figs. 2, 3) smooth, without a trace of pro- or retrolateral rows of marginal denticles, surface finely granulate, unarmed except for scattered erect macrosetae and a few scattered denticles along distal margin. Trochanters relatively smooth on lateral and medial surfaces, with a few denticles and setae on pro- and retrolateral surfaces. Femora without pseudoarticulations; patellae unremarkable; tibiae II with 3 pseudoarticulations, all others without pseudoarticulations; basitarsi with pseudoarticular formula 3–4,6–7,4,3–6; telotarsi and claws unremarkable.
Penis (Fig. 13). Ventrolateral sacs large, voluminous, extending longitudinally from glans-shaft articulation to about one-fourth to one-third length of shaft; sac openings wide, region around opening reinforced with collar-like sclerotization. Shaft broad posteriorly, tapering gradually to level of sac opening then narrowing abruptly at glansshaft junction forming neck; glans slightly wider than neck. Dorsoproximal margin of basal hemocoelic opening to shaft posterior to ventral margin creating large ventroposterior opening. Shaft rather thick in lateral perspective and increasing in thickness posteriorly due to median longitudinal bulge that continues to posterior ventral margin. Stylus slightly less than half the length of glans.
Coloration (Figs. 1–3). Dorsum mainly dark toasted brown. Light brown mottling on carapace anterolateral to ocularium. Ocularium dark brown, each lens bordered by thin yellow line dorsally, line broadening posteriorly and ventrally, terminating anterolaterally at large patch of white at anterolateral base of ocularium. Medial margin of ozopore light brown. Dark median mark delimited laterally by lighter mottling, especially on scutal tergite 1, increasingly indistinct posteriorly. Pleural and intertergal membranes very dark brown with dense array of irregular white flecks, very obvious laterally, appearing dorsally as thin stripes separating meso- and metapeltidium, scutum, free tergites; membrane between last free tergite and anal operculum pure white. Anal operculum variable.
Venter (Fig. 2). Coxapophyses light yellow-brown. Genital operculum mottled with shades of brown, somewhat lighter medially, sometimes with short, fine anterior median stripe; anterior lip and anterior lateral margins yellow-brown. Sternites with mottled shades of brown anteriorly, yellowish posteriorly, with transition corresponding roughly to transverse row of setae.
Chelicera. Basal article mottled dark and light brown; second article nearly uniform toasted brown, but fixed and moveable fingers of chela abruptly yellow-brown with dark termini.
Palp. Coxa yellow; trochanter light brown; femur, patella, tibia and tarsus dark toasted brown, but tip of tarsus somewhat lighter.
Legs. Coxae dark toasted brown on distal (dorsal) surfaces but dark color increasingly restricted to exposed pro- and retrolateral surfaces proximad (ventrad) along coxa (marginal pro- and retrolateral surfaces light brown); middle and extreme proximal (ventral) surfaces a lighter brown but punctuated by dark-brown sigilla. Trochanters dark brown on ventral, prolateral and retrolateral surfaces, lighter but mottled with dark brown on dorsal surfaces. Base and terminus of femur light brown but remaining portion of femur, patella and tibia dark brown. Sometimes with slight evidence of alternating dark and light banding on femoral shaft. Basi- and metatarsi light brown.
Description of female. Measurements of female allotype (in mm). Body length, 6.4, carapace length, 2.0., carapace width, 2.5. Palp: femur 1.3, patella 0.6, tibia 0.9, tarsus 1.6. Legs (femur, patella, tibia, basitarsus, telotarsus): I: 6.2, 1.5, 4.9, 8.3, 9.1; II: 10.4, 1.8, 10.3, 10.5, 11.2; III: 6.1, 1.5, 4.7, 7.8, 9.3; IV: 6.0, 1.4, 5.0, 6.7, 8.7.
Dorsum. Carapace, scutum and free tergites finely granulate; carapace without crenulation of male; small, low rounded tubercles of male opisthosoma absent or limited to first three scutal tergites. Otherwise unarmed except for scattered setae. Supracheliceral lamina, anterior carapacal margin, ocularium and ozophore as in male (Fig. 11).
Venter (Fig. 5): Labrum not inflated or arrowhead shaped, terminus tapering but with scattered minute denticles, not as dense as in male. Venter finely granulate; sternites unarmed except for scattered short erect setae; genitial operculum with wide, glabrous anterior lip delimited posteriad by prominent submarginal sulcus, low transverse ridge delimited anteriorly by submarginal sulcus and posteriad by weakly procurved sulcus, ridge with imperfect row of erect setae; otherwise operculum armed with scattered erect setae.
Chelicerae. Basal article with retrodorsal longitudinal row of a few setae, row bends medially near distal margin. Second segment with stiff, protrorse bristles on medial surface, increasing in density distally to form tuft near base of fixed finger, a few long setae near base of chelal fingers.
Palps (Fig. 7, 8). Unarmed except for setae. Femur with erect macrosetae on dorsal and ventral surfaces, pro- and retrolateral surfaces almost bare. Patella without distoprolateral apophysis. Patella, tibia and tarsus with erect macrosetae; tibia and tarsus with coat of distally recumbent microsetae. Tarsus longer than patella and tibia combined. Claw lacking well-developed teeth, but a few small denticles may represent vestigial teeth.
Legs. Shorter and more robust than in male, but otherwise similar, including same number of tibial pseudoarticulations, basitarsal pseudoarticulations 3,6,4,6
Coloration (Figs. 4–6). Dorsum. Propeltidium with dark-brown triangular region enclosing ocularium, with apex at mid-anterior margin and base formed by posterior margin; brown interrupted by bilateral light and dark sigillary spots and a pair of light spots at base of ocularium. Ocularium whitish at base and carinae, central furrow dark brown; lenses outlined in black. Supracheliceral lamina and region anterior to ozophore dark brown, with a bilateral pair of distinct white lines along lateral anterior border of the carapace. Lateral surfaces of carapace dominated by whitish color with thin, dark marginal line, dark line outlining margin of ozopore and two elongate, dark submarginal spots. Mesopeltidium offset from propeltidium by dark transverse sulcus. Meso- and metapeltium with broad dark median band with reticulated mottling of buff spots; intertergal membranes dark brown with numerous white flecks; laterally with prominent whitish blotches and flecks.
Scutal tergites with dark longitudinal central figure continuing from carapace, distinct anteriorly but margins degrading posteriorly. Central figure of each scutal tergal region and first free tergite dark with numerous small buff flecks; lateral margin of central figure indicated by nearly pure black region on all tergites, contrasted by white region (tergite 1) or large buff or white spots, lateral margin of each terminating in large whitish spot, thus forming a longitudinal row of whitish spots. Each scutal and free tergite with medial pair of white spots, those of last scutal tergite within an irregular transverse whitish band. Intertergal regions of scutum with comparatively uniform dark cuticle and buff flecks, appearing as a continuation of flexible pleural cuticle. Last free tergite and anal operculum light mediad, darker laterad, but medial and lateral white spots still present on last free tergite.
Venter (Fig. 5).Venter much lighter than dorsum, whitish with fine dark mottling in irregular transverse patterns, intersegmental sigilla dark brown; dark transverse bands contrasting with light sternites in lateral perspective. Genital operculum whitish with subtriangular midregion of fine dark mottling.
Chelicerae. Basal segment dark brown prolaterally, light brown retrolaterally with two regions separated by white, setae occupying white region; second segment darker brown retrolaterally and lighter brown prolaterally divided centrally by whitish stripe, all fading to light yellow brown distally; chelal fingers light yellow-brown with dark tips.
Palps. Coxa, trochanter and prolateral to ventral surfaces of femur yellow-brown, femur brown on retrodorsal surface and distoprodorsal surface but these two regions divided dorsally by yellow-brown stripe extending from prolateral surface. Patella brown with yellow-brown distal margin. Tibia brown at proximal margin but brown area continuing distally on dorsal surface and gradually tapering distaf, remainder yellow-brown. Tarsus yellow-brown but with darker patch on subterminal ventral surface.
Legs. Coxae dark brown distad, extending along exposed pro- and retrolateral surfaces narrowing ventrad (extreme pro- and retrolateral surfaces lighter brown), dark brown gradually replaced on exposed pro- and retrolateral surfaces by brown sigilla embedded in lighter cuticle, sigilla become increasing lighter ventrally; center of coxal surface with large, irregular whitish mark. Trochanters dark brown on prolateral, retrolateral and ventral surfaces, dorsal surface whitish bisected by dark longitudinal stripe, surface with clusters of fine, dark-brown sigilla and mottling. Femora dark brown at base followed by alternating series of broad light- and dark-brown bands terminating in light band. Patellae dark brown, mottled with light brown, especially at proximal and distal ends. Tibia brown with irregular narrow or broad dark-brown bands, with brown mottling distally. Basi- and telotarsi yellowish brown.
description: Published as part of Shultz, Jeffrey W., 2018, A new species of Leiobunum from Arizona, U. S. A. highlights the limits of typological classification in harvestmen (Opiliones: Sclerosomatidae: Leiobuninae), pp. 67-75 in Zootaxa 4370 (1) on pages 69-74, DOI: 10.11646/zootaxa.4370.1.5, http://zenodo.org/record/1138538