Antrodiaetus microunicolor Hendrixson & Bond, 2005, new species
Creators: name: Hendrixson, BRENT E.
name: Bond, Jason E.
Publisher: name: Zenodo
Year: 2005
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Araneae
Antrodiaetidae
Antrodiaetus
Antrodiaetus microunicolor

description: Antrodiaetus microunicolor new species
(Figures 1, 6-8, 11-14; Tables 1-2)
Type data. - United States: North Carolina: Macon County: Coweeta Hydrologic Station (LTER) Watershed 2 (35.07 ° N, 83.44 ° W), 24 November 1978 (L. Reynolds), male holotype (UNSM); ditto, 19 December 1978, in pitfall traps (L. Reynolds), 8 paratype males (NCSM); ditto, 25 October 2003 (B. E. Hendrixson), 2 paratype females (ECU- USNM, MY 2401, 2402); ditto, 8 November 2003 (B. E. Hendrixson), 1 paratype male, 1 paratype female (ECU-USNM, MY 2425, 2422). Coweeta Watershed 7 (35.06 ° N, 83.44 ° W): 19 December 1978, in pitfall traps (L. Reynolds), 2 paratype males (NCSM). Coweeta Watershed 14 (35.05 ° N, 83.43 ° W): 25 October– 8 November 2003, in pitfall traps (B. E. Hendrixson), 2 paratype males (ECU-USNM, MY 2420, 2421). Coweeta Watershed 18 (35.05 ° N, 83.44 ° W): 15 November 2003 (B. E. Hendrixson, P. E. Marek & D. A. Beamer), 1 paratype female (ECU-USNM, MY 2448). Coweeta Watershed 36 (35.06 ° N, 83.47 ° W): 15 November 2003 (B. E. Hendrixson, P. E. Marek & D. A. Beamer), 1 paratype female (ECU-USNM, MY 2441).
Diagnosis. - The new species appears to be most closely allied to Antrodiaetus unicolor. Males of the new species are readily identified by the following characters (Coweeta A. unicolor characters in parentheses): exceptionally small size: CL <4.50 mm (CL> 5.60 mm); the absence of macrosetae on the ventral, distal surface of metatarsus I (at least one macroseta usually present); and breeding season: late October through December (September through mid-October). In addition, males of the new species have a slightly more robust pedipalp tibia, although the ranges between the two species are more or less continuous: PTiL / PTiD = 2.09 - 2.24 (2.26 - 2.52). Females of both species are fairly homogeneous in morphology (Figs. 1 A– 1 B) and pose some problems with identification, although the following characters may provide some diagnostic utility (Coweeta A. unicolor characters in parentheses): smaller size: CL <7.00 mm (CL> 7.00 mm); lighter coloration: dorsal shield of prosoma, legs, and tergite usually yellowish-brown (dark chocolate brown); and convergent median dorsal setae just posterior to pedicel thin, sometimes somewhat thickened, and tapered (thorn-like); the latter character appears to work well for identifying immature specimens from Coweeta as well. The following morphometric ratio may provide some value: IVMeL / CL = 0.52 - 0.57 (0.59 - 0.61).
Antrodiaetus microunicolor new species can be differentiated from A. robustus by some of the same characters (A. robustus characters listed in parentheses, Coyle 1971): smaller size (male CL 5.40 - 6.60 mm; female CL 6.20 - 9.30 mm); male metatarsus I macrosetae (usually with macroseta A and B present). They also differ by the male prolateral tibia I macrosetae (less than one-fifth ensiform).
Description. Holotype male: Coloration (in alcohol): Specimen has been preserved for over 25 years and appears to have been bleached; we have decided to describe the coloration of a recently collected specimen instead. Base color of dorsal shield of prosoma, pedipalps, legs II–IV light grayish-tan, distal segments lighter. Eyes underlined with black pigment. Femur I light grayish-tan; patella I grayish-brown; tibia, metatarsus, tarsus I orangish-red. Chelicerae darker than dorsal shield of prosoma. Sternum pale grayish-yellow, labium darker. Opisthosoma purplish-gray; tergites darker than opisthosomal surface; second tergite somewhat darker than dorsal shield. Prosoma: Head region slightly elevated from thoracic region. Setae moderately dense along peripheral edges of dorsal shield; setae sparsely distributed on dorsal surface of dorsal shield of prosoma posterior to foveal groove. Sternum and labium moderately to densely setose. Opisthosoma: Three heavily sclerotized patches on dorsal surface; posterior patch smaller than others but mostly continuous with the second. Entire opisthosomal surface densely covered with setae, interspersed with some slightly more elongated and thickened setae posteriorly; tergites accompanied by a few thickened setae. Ventral surface of opisthosoma with 25 epiandrous gland spigots located just anterior to genital opening. Chelicerae: Anterior dorsal prominence weak. Upper ectal (retrolateral) surface devoid of setae. Pedipalps (Fig. 6): Tibia moderately robust (PTiL / PTiD = 2.14). ICS tip below level of OCS; ICS tip well-sclerotized, tapered to a narrow point; OCS tip well-sclerotized, blunt, weakly serrated. Leg I: Mating clasper consisting of 16 ensiform, 5 attenuate macrosetae, centered at approximately 2 / 3 distance from proximal to distal end of tibia (Fig. 7). Prolateral, ventral, distal aspect of tibia with a macroseta. Retrolateral, ventral aspect of tibia with 4 ensiform, 1 attenuate macrosetae; distal-most macroseta of group positioned at approximately 2 / 3 distance from proximal to distal end of tibia. Prolateral, ventral aspect of tibia with 5 ensiform macrosetae. No macrosetae present on ventral aspect of metatarsus (Fig. 7). Metatarsus slightly sinuous in ventral view. Measurements (mm): CL = 4.50; SL = 2.25; SW = 2.00; CT (l / r) = 10 / 9; PFeL = 2.70; PTiL = 2.35; PTiD = 1.10; IFeL = 4.10; ITiL = 2.85; IMeL = 3.15; ITaL = 1.85; ALD = 0.28; AMD = 0.12; ALS = 0.38; AMS = 0.16; OQW = 0.88.
Paratype female (MY 2402): Coloration (in alcohol): Dorsal shield of prosoma, opisthosomal tergite, pedipalps, and legs yellowish-brown, head region slightly darker. Eyes underlined with black pigment. Chelicerae light brown. Sternum orangish-brown, labium darker. Abdomen yellowish-brown with faint purple pigment posterior of tergite; cordate mark weakly indicated as pale longitudinal band along midline. Prosoma: Head region strongly elevated from throacic region. Setae moderately dense along peripheral edges of dorsal shield of prosoma; setae sparsely distributed on dorsal surface of dorsal shield of prosoma posterior to thoracic groove. Sternum and labium moderately to densely setose. Sternum with three pairs of sigilla, anterior-most pair somewhat reduced. Opisthosoma: Spermathecae (Fig. 8) consisting of four receptacles; stalk and bowl well-sclerotized; stalk not expanded basally; bulb somewhat flattened. Dorsal background setae sparsely to moderately long; tergite with a few thickened setae. Convergent median dorsal setae just posterior to pedicel thin and tapered, not thorn-like (see Figs. 9 - 11 for a comparison with Antrodiaetus unicolor). Chelicerae: Rastellum well-developed. Upper ectal (retrolateral) surface devoid of setae. Measurements (mm): CL = 5.25; SL = 2.88; SW = 2.44; CT (l / r) = 12 / 11; PFeL = 2.70; IFeL = 3.70; ITiL = 2.30; IMeL = 2.10; ITaL = 1.25; IVFeL = 3.50; IVTiL = 2.05; IVMeL = 2.90; IVTaL = 1.30; ALD = 0.34; AMD = 0.14; ALS = 0.54; AMS = 0.16; OQW = 1.20.
Variation. - A total of 14 males and five females were studied from Coweeta. Three males lacked a macroseta on the prolateral, ventral, distal aspect of tibia I (a character also found in some males of Antrodiaetus unicolor). A very small male (MY 2421, CL = 3.60 mm) had macroseta A on the ventral aspect of metatarsus I, but we tentatively assign it to A. microunicolor new species on the basis of its size and breeding season. One female (MY 2441) had moderately more thickened convergent medial dorsal setae on the opisthosoma just posterior to the pedicel. However, these setae do not appear as well developed and thorn-like as they do in females of A. unicolor from Coweeta (Fig. 10), and look to be broken at their apices (i. e., they do not appear tapered). Because of their small size, adult females were identified solely on the basis of whether they contained offspring in their burrows. The lower limit of the length of the dorsal shield of prosoma for adult females is unknown. One female (MY 2401) is fairly large (CL = 6.88 mm), nearly as big as the smallest confirmed adult females of A. unicolor, but its dorsal shield color and opisthosomal convergent medial setae compare favorably to the other specimens belonging to the new species. A summary of measurements can be found in Tables 1 and 2.
Remarks. - Populations of Antrodiaetus unicolor (as delineated by Coyle 1971) containing unusually small males (i. e., CL 4.00 mm) were also examined to determine the diagnostic utility of the metatarsus I macrosetal character. Small males from Pittsburgh, Pennsylvania (population A of Coyle 1971) and Duke Forest, North Carolina (population N) each possess macroseta A. The diminutive male that Coyle (1971) examined from west of Lake City, Tennessee (population L) was unavailable for study.
At least three other populations of Antrodiaetus containing unusually small adult females (as determined by the presence of offspring in their burrows) have been discovered throughout the course of fieldwork in western North Carolina and eastern Tennessee. These spiders compare favorably to females of A. microunicolor new species, but adult males are unavailable from these sites and we choose to hold off assigning them to any particular species at this time.
Before establishing Antrodiaetus microunicolor new species, other available names (i. e., those synonymized under A. unicolor) were considered for resurrection. As discussed above, Hentz (1841) described the species Mygale gracilis from Alabama, but the holotype was destroyed, and therefore, its exact identity is unknown; Coyle (1971) synonymized this name with A. unicolor and we feel that decision is well justified and should be maintained. Atkinson (1886) described two species, Nidivalvata marxii and N. angustata, from Chapel Hill, North Carolina. These two “species” are likely conspecific with material examined from Duke Forest in Durham and Orange County, North Carolina; these populations, located within the eastern piedmont, are at least 400 kilometers from Coweeta and are not conspecific with A. microunicolor new species. Finally, Simon (1884) described Brachybothrium accentuatum on the basis of an immature female from North Carolina. This specimen does not share characters indicative of the new species from Coweeta (e. g., thin and tapered setae). In addition, because immature mygalomorph spiders are nearly impossible to identify due to their lack of diagnostic characters, and because the precise location within North Carolina is unknown, we agree with Coyle’s (1971) decision to synonymize and maintain this name under A. unicolor.
Distribution. - The new species is presently known only from the type locality, at the Coweeta LTER site in the southern Appalachian Mountains near Otto, North Carolina (Fig. 2).
Etymology. - The specific epithet refers to the diminutive size of this species and its affinity to Antrodiaetus unicolor.
description: Published as part of Hendrixson, BRENT E. & Bond, Jason E., 2005, Two sympatric species of Antrodiaetus from southwestern North Carolina (Araneae, Mygalomorphae, Antrodiaetidae), pp. 1-19 in Zootaxa 872 on pages 10-13, DOI: 10.5281/zenodo.10086