Acanthopachylus aculeatus ( Kirby, 1819 ), 1923

Acosta, Luis E., 2021, The return of a forgotten harvestman: revalidation of Gonyleptes robustus Holmberg, 1876, as the second species of Acanthopachylus Roewer, 1913 (Arachnida, Opiliones, Gonyleptidae), Zootaxa 5040 (3), pp. 428-438 : 428-438

Acanthopachylus aculeatus ( Kirby, 1819)

( Figs. 1A–B , 2A–B )

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Gonyleptes aculeatus Kirby 1819: 452 . Types: not specified in the original description, at least one male, D. Hancock leg. (supposed by Roewer 1923 to be in BMNH); not found, presumably lost.

Gonyleptes acanthurus Perty 1833: 202 [name made available by indication to Duméril’s (1823) illustration of the “Facheur acanthure”: Pl. 60, figs. 14–16; cf. ICZN Art. 12.2.7.]. Types:? (not found). Synonymy by Butler (1873).

Pachylus aculeatus: Sørensen 1884: 641 (in part) [= Gonyleptes robustus , synonymy incorrect].

Acanthpachylus aculeatus: Roewer 1913: 51 (in part), NEC figs. 19, 20 [drawings display A. robustus comb. nov.].

Acanthopachylus aculeatus: Roewer 1923: 412 (in part), NEC figs. 507, 508 [drawings are A. robustus comb. nov.]; Mello- Leitão 1939 (in part): 623 [“Toute l’Amérique du Sud du coté atlantique”]; B. Soares & H. Soares 1954: 233 (in part); Ringuelet 1953 (in part): 161 [= Heteropachyloidellus serrulatus , synonymy incorrect, referable to A. robustus comb. nov.]; 1955 (in part): 283–288 [= Heteropachyloidellus robustus , correct under A. aculeatus ; also the following incorrect synonymies: = Pachyloidellus fuscus , referable to Pachyloidellus butleri (cf. Acosta 1993); = Heteropachyloidellus dimorphicus = H. paucigranulatus = H. marginatus = Pachyloidellus tricalcaratus , all referable to A. robustus comb. nov.]; 1959 (in part): 275 [= Pachylus mesopotamogalis , synonymy referable to A. robustus comb. nov.]; H. Soares & B. Soares 1986: 87, figs. 1–2 (in part) [= Guascaia ypsilonota , synonymy referable to A. robustus comb. nov.]; Kury 2003: 154 (in part). NEC: Acosta 2002: 81 (new material cited as A. aculeatus , corresponds to A. robustus comb. nov.); Acosta & Maury 1998: 580.

Heteropachyloidellus robustus Roewer 1943: 18 , Pl. 1, fig. 6 [Types: SMF, ♂ ♀ Montevideo, Uruguay, examined]. Synonymized by Ringuelet 1955. [Potential junior homonym of Acanthopachylus robustus ( Holmberg 1876) comb. nov.; replacement name not applicable while under synonymy: ICZN Art. 11.6.].

Identification. Kirby (1819) described the spine-shaped apophysis on area V of male as “ spina aculeiformi validissima, incurva, acuta, basi sinistrorsum bidentata, dextrorsum unidentata ” [= a strong sting-like spine, curved, acute, base bidentate on the left, unidentate on the right]. As stated in the key above, one main difference between A. aculeatus and A. robustus comb. nov. is the shape, size and curvature of this apophysis: that of A. aculeatus being large and curved ( Fig. 2B , “ spina aculeiformi validissima, incurva, acuta ”), not inclined upwards as in A. robustus comb. nov. ( Fig. 2D ); moreover, the apophysis is frequently accompanied by additional apophyses on the sides in A. aculeatus ( Fig. 2A , “ basi sinistrorsum bidentata, dextrorsum unidentata ”), only seldom in A. robustus comb. nov. ( Fig. 2C ). Also, Kirby’s (1819) reference to femur IV (“ Femora postica fusca, nodulosa, subtus prope basin spina validissima obtusa ” = rear femora dusky, knotty, ventral close to the base a powerful blunt spine) likely reflects one specific difference, considering that the basal large, blunt apophysis (“ spina validissima obtusa ”) of A. aculeatus ( Fig. 2A ) is replaced by a truncated one in A. robustus comb. nov. ( Fig. 2C ). In this description there is no reference to any strong femoral curvature, a remarkable feature in A. robustus comb. nov. ( Fig. 2D ), so the later species does not seem to be involved.

Type locality. “Brasilia” (obviously meaning the country, not the present capital city); Montevideo, Uruguay, is presumed to be the probable locality for Kirby´s (1819) materials (see next section) .

Distribution. Restricted to southeastern Uruguay (Departamentos Florida, Canelones, Montevideo, Lavalleja, Maldonado and Rocha), reaching marginally the southernmost tip of Brazil along the Atlantic coast ( Fig. 3 ). A controversy may arise from Kirby’s (1819) statement: “Habitat in Brasilia”, what might suggest its occurrence somewhere in Brazil, not in Uruguay. With such old collections one should always be aware of potential mislabellings, so inaccuracies are to be expected; very often specimens were obtained during long-lasting ship expeditions, making port localities the most probable collecting points. At the early XVIIIth century, “ Brazil ” was, for many Europeans, much like a coarse geographical reference instead of a precise locality or country. However, it is worth noting that in 1816 the United Kingdom of Portugal, Brazil and the Algarves invaded and appended de facto the present Uruguayan territory (at that time still a part of the Provincias Unidas del Río de la Plata, four years later formalized as the Brazilian-Portuguese Provincia Cisplatina); invaders occupied the port-city Montevideo at the beginning of 1817 ( Halperin Donghi 2000). Thereby, even if the precise collecting date of A. aculeatus is unknown, the original reference can be considered consistent with the known range of the species.

Figures

FIGURE 1. Live males of Acanthopachylus aculeatus (A–B: El Caracol, Departamento Rocha, Uruguay; photos by Javier A. Canteros), and Acanthopachylus robustus comb. nov. (C–D: Lago Lugano, Buenos Aires, Argentina; photos by Ricardo A. Palonsky—RAP).All photos used with permission of the authors.

FIGURE 2. Diagnostic characters to distinguish male Acanthopachylus aculeatus (A–B) (MHNM, Departamento Lavalleja, Uruguay) and Acanthopachylus robustus comb. nov. (C–D) (LEA 000.428, Sierra de la Ventana, Buenos Aires Province, Argentina). A, C: dorsal scutum, coxae, trochanter and femur IV, dorsal view; B, D: coxa (with rear end of body), trochanter, femur and patella IV, prolateral view. Scale bars: 1 mm.

FIGURE 3. Geographical distribution of Acanthopachylus aculeatus (Kirby) (blue dots) and A. robustus (Holmberg) comb. nov. (red dots) in Argentina, Uruguay and southern Brazil. Records with verified taxonomic identity are denoted with full color symbols, small white dots represent literature citations not checked as yet. Ecoregions according to Olson et al. (2001); both grassland-type ecoregions (Humid Pampas on the Argentinean side, Uruguayan Savanna in Uruguay and southern Brazil) are given the same color (light yellow). APAF: Alto Parana Atlantic Forests; HCH: Humid Chaco; MS: Southern Cone Mesopotamian Savanna; ESP: Espinal. Inset (bottom right): location of the area represented in South America.