The family Opilioacaridae (Acari: Parasitiformes) in Argentina, with description of two new species

Two new species of Neocarus, N. entrerios n.sp. and N. misiones n.sp., are described for both adult instars, with locality data for a few additional records of unidentified specimens. Most Argentinean records are from the Northern and Eastern border regions. Even so, current results suggest that opilioacarid diversity in Argentina, while modest, is likely to include several more species.


Introduction
The first species of Opilioacaridae described from the New World was Opilioacarus platensis Silvestri 1905, based on seven specimens collected from Salto, Uruguay (31.4167°S 57.0000°W) and Posadas, Misiones, Argentina (27.3667°S 55.9000°W) (Silvestri, 1905). The species was later reclassified as Neocarus platensis (Vázquez and Klompen, 2009). As expected given its age, the description of N. platensis lacks some detail in terms of relevant morphological characters, specifically for the ovipositor, but a more troubling item is that the author also failed to designate a holotype among the specimen series studied. This could be important because Silvestri apparently did not recognize any differences among the specimens from the two localities, an issue amplified by Van der Hammen, who redescribed O. platensis based on material from a third site, Sinimbu (listed as Sinumbu), Rio Grande do Sul, Brazil (29.500°S, 52.5000°W) (Hammen, 1969). Studies of Opilioacaridae in Mexico, Madagascar, and Brazil (Vázquez and Klompen, 2002;2009;2010;Bernardi et al., 2012;Bernardi et al., 2013;Araújo et al., 2018;Bernardi and Borges-Filho, 2018) have shown that many species of Opilioacaridae have quite localized distributions. On the other hand, the north temperate species N. texanus Chamberlin and Mulaik, 1942, may have a very broad range, from Central Texas, west to Arizona (both U.S.A.), and south to Guerrero, Mexico (Vázquez and Klompen, 2015), sites separated by more than 1000 km. This leaves two unanswered questions: 1) are the specimens collected from these three disparate south temperate localities (separated from each other by 410-470 km) indeed conspecific (mirroring the broad distribution of N. texanus in North America), or do they represent more than one species? 2) What is the species level diversity of Opilioacaridae in the temperate regions of South America?
The focus of this study is solely on the second question. To this end we examined material in the holdings of the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, Argentina. This material includes specimens of two species that are different from N.

Materials and methods
Most material was studied as slide-mounted specimens. For this purpose, specimens were dissected, cleared in lactic acid and mounted on slides using Hoyer's medium (Walter and Krantz, 2009). Due to the considerable size of these mites, specimens were dissected, with different parts of a single mite mounted on several different slides or using multiple cover slips on a single slide. Terminology for the palp tarsal sensilla follows Grandjean (1936) as modified by Vázquez and Klompen (2002), for the sternitogenital region we follow Klompen et al. (2015), and for the leg sensory structures Grandjean (1936), Van der Hammen (1966), and Araújo et al. (2018). Characters were processed in the data matrix development mode of vSysLab (Johnson, 2010) and were exported as proto-species descriptions. Drawings were prepared using a Zeiss Axioscope 3 phase contrast microscope, connected to a drawing tube, measurements were taken using an ocular micrometer and are presented in micrometers (μm). Most measurements are summarized in Table 1. Collections were made by hand, with specimens collected from under stones or rotting bark and preserved in alcohol. Many of the newly examined specimens were collected in

Taxonomy
Genus Neocarus Chamberlin and Mulaik, 1942 All specimens examined in this study are assigned to the genus Neocarus Chamberlin and Mulaik, 1942. Generic assignment is based on the following characteristics. In the adults 3 setae on the penultimate body segment (0 or >3 in all Old World taxa and Amazonacarus Vázquez et al., 2014;shared with Caribeacarus Vázquez andKlompen, 2009 andBrasilacarus Vázquez et al., 2015), 4-6 foliate setae on the palp tarsus (>7 in Caribeacarus and Brasilacarus), eupathidium zeta-1 (ζ1, the sensillum with a "crown-like" tip) in the main sensillar group of tarsus I (usually distal in Caribeacarus), and shiny fleshy setae with a whip-like tip absent from the palps (present in Brasilacarus). Within Neocarus the Argentinean specimens share a few characteristics suggesting that they may be related: palp tarsus in adults carries 6 large, foliate sensilla with 4 prominent lobes (usually 3 lobes) and both pairs of genital glands in the males are distinct, large, and similar in size (generally indistinct in cleared specimens, or anterior pair much smaller than posterior).

Idiosoma
Color. Dark blue and violet stripes on both body and legs. Body often with brownish background reflecting ingested food.
Dorsum. Prodorsal shield in adults with 142(M)-164(F) setae (N=1 for both) and two pairs of lateral eyes. One pair of prodorsal lyrifissures present (Fig 3A, grey arrow). Setae somewhat rounded and "puffed-up" (Figure 3, detail). Sexual dimorphism in setal shape or setal arrangement minimal (setae in female appear slightly larger). Dorsal idiosoma between the shield and the preanal segment without setae, but with numerous lyrifissures arranged in transverse rows. Setation of preanal segment limited to 1 dorsal, and 2 ventro-lateral setae. Anal valves with 10-16 setae each, with females showing higher numbers.  Sternitogenital region (Figure 4). Sternal verrucae in adults each with 3-4 large, serrate and pointed, and 1 composite (St1) seta. Setae St1 subequal in size to St5. Setae St2 and St3 in females and males barbed, tapering to a fine tip. Remaining sternal region with 4-6 pairs of stout, ribbed, setae with rounded tips. Pregenital capsules each with 1 long, tapering seta (St5) and 4-6 stout, ribbed, blunt-tipped setae. Pregenital and genital areas in female with, respectively, 0 and 12-13 sturdy, lightly ribbed and barbed, tapering setae ( Figure 5A). Male with 8-9 setae in pregenital region, mostly thick, ribbed and blunt, but a few lightly ribbed and tapering. Genital region 7-9 barbed, lightly ribbed, tapering setae ( Figure 5B-C). Ovipositor ( Figure 6) without terminal setiform sensilla, but with three very distinct roundish terminal lobes. Without well sclerotized internal structures. Terminal area in one female (the only one where this area was fully visible) covered by a bilobed membrane/tectum ( Figure 6A, arrow). Male genital valves rectangular to curved, not triangular. Male glands well developed, both pairs of similar size (Figure 7).
Comparative notes -This comparison is limited to described Neocarus species from South America, with exception of N. ojasti Lehtinen, 1980. The description of N. ojastii does not provide sufficient detail for an adequate comparison. Comparisons with N. platensis are based on the original description by Silvestri (1905), the re-description by Van der Hammen (1969) based on Brazilian material, and comments and notes by Marcel Santos de Araújo based on examination of the type series.
Neocarus misiones differs from N. coronatus Araújo et al., 2018 by the absence of distinct sexual differentiation in the setation of the prodorsal shield, and the presence of 6, rather than 4, d setae on the palp tarsus; from N. potiguar Bernardi et al., 2012, N. proteus Bernardi et al., 2013, andN. platensis by the absence, vs. presence, of pregenital setae in the female (Hammen, 1969;Araújo, pers. comm.). It differs from N. caipora Bernardi et al., 2014 andN. spelaion Bernardi andBorges-Filho, 2018 by the different shape of the genital setae in the female (sturdy and ribbed vs. thin and smooth), and the presence of 4, rather than 3 lobes on the d setae on the palp tarsus (N. caipora only).
Description -Based on 4 females and 3 males. Immatures unknown. Gnathosoma Chelicera ( Figure 9A). Basal segment in adults with 1 seta, fixed digit with 3, one of which (ch1") distinctly larger. Seta cht on basal segment of male chelicera shorter than seta ch1'' on fixed digit. Setae ch2', ch2'' and cht in males simple, with an attenuated tip. One large, somewhat blunt, ventral denticle on movable digit in all adults. Axial scale-like processes on movable digit in both adults absent.
Idiosoma Color: Violet-blue with the usual banding pattern. Color observed for alcohol preserved specimens only.
Dorsum. Prodorsal shield with two pairs of lateral eyes. One pair of prodorsal lyrifissures present. Setation in females and males consisting of, respectively, 186-204 and 218-242 setae. Sexual dimorphism in anterior portion of prodorsal shield (between anterior margin and lyrifissures) distinct, with a dense grouping of 56-62 setae in males ( Figure 11A) vs. 22-24 in females ( Figure 11B). Setal density in anterior area of females similar to that on the remaining shield. All setae somewhat rounded in appearance and "puffed-up" (Figure 11, detail). Dorsal idiosoma between the prodorsal shield and the preanal segment without setae, but with numerous lyrifissures arranged in transverse rows. Setation preanal segment limited to 1 dorsal, and 2 ventro-lateral setae. Anal valves with 12-16 stout, ribbed setae (14-16 in females; 12-16 in males).
Collection  Etymology -The specific name is derived from the primary collection locality, Entre Rios province, Argentina.
Comparative notes -Neocarus entrerios differs from N. potiguar, N. proteus, and N. platensis from Brazil by the absence of pregenital setae in the female. It differs from N. coronatus by the presence of 6 (vs. 4) foliate setae on the palp tarsus; from N. potiguar, N. caipora, N. platensis (from Argentina and Uruguay) and N. misiones by the absence (vs. presence) of p-type setae on the palp genu (N. proteus and N. spelaion are somewhat intermediate as they carry small numbers (1-7) of p-type setae on the palp genu), and from N. spelaion by the uniformity (vs. variability) in shape of the pregenital and genital setae in the male. Neocarus entrerios differs from N. misiones by the shape and number of genital setae in the female, the structure of the ovipositor, and the presence (vs. absence) of sexual differentiation in the setae on the prodorsal shield.

Discussion
The diversity of Opilioacaridae in Argentina is likely to be higher than indicated by the three species (including the two new ones) currently recorded from that country. We have been able to study a few specimens from other localities, and it appears that these may represent additional species. Unfortunately, all collections involve singletons, insufficient for an adequate description. The collection data for these specimens is listed to provide a better record of known diversity in the group in Argentina. Notably, most records so far are all from the northern and eastern border areas (Figure 14