New records of the water mite genus Arrenurus Dugès, 1834 from South America (Acari: Hydrachnidia: Arrenuridae), with the description of five new species and one new subspecies

New records are presented of the water mite genus Arrenurus from Argentina, Bolivia and Surinam. Five new species are described, i.e. Arrenurus mansoensis n. sp., A. niger n. sp., A. stagnalis n. sp., A. surinamensis n. sp. and A. tempelmani n. sp., and one new subspecies, i.e. A. tenuicollis lacustris n. subsp. Arrenurus soesilae Makan, 2005 is synonymized with A. epimerosus Marshall, 1919.


Introduction
The water mites genus Arrenurus Dugès, 1834 is the most species-rich of the Hydrachnidia, with worldwide nearly 1000 species described (Joel Hallan pers. comm.). A list of South American water mites species was published by Rosso de Ferradás & Fernández (2005) who listed 150 Arrenurus species. However, Arrenurus (Micruracarus) incurvatus K. Viets, 1954, Arrenurus (Micruracarus) perspicillatus K. Viets, 1954 and Arrenurus (Dadayella) nanus K. Viets, 1954 were not included. Since then, two more Arrenurus species were published from South America, though based on females only (Rosso de Ferradás 2006a, Makan 2005, but see below). The number of Arrenurus species from South America tallies now 153 species. Besseling (1949) described Dadayella hirtipalpis from Surinam and K. Viets (1954a) described Arrenurus (Dadayella) guttifera from Brazil. These species are listed by Rosso de Ferradás & Fernández (2005) as Arrenurus (Dadayella) hirtipalpis and Arrenurus (Dadayella) guttifera, respectively, but I agree with Cramer & Cook (1992) that these species do not belong to Dadayella. However, as these two species are known in the female sex only, they cannot be accurately assigned to a subgenus.
Based on previous information, the arrenurids of South America are assigned to the following subgenera: Arrenurus s.s. 19 species, Megaluracarus 91 species, Micruracarus 2 species, Truncaturus 4 species, Arrhenuropsides 2 species, Arrhenuropsis 2 species, Brevicaudaturus 2 species, Dadayella 6 species and 25 species from the female only that cannot be attributed to a subgenus.
The study of the genus Arrenurus in South America is hampered by descriptions of species based on either males or females only. It must be stressed that new species should not be described based on females only. Females often show a large variation in characteristics (shape of idiosoma and genital plates), and identification of females is notoriously difficult. Material examined -Argentina. Entre Ríos Province: 1/2/0, ditch at Brazo Largo, N of Zarate, 33°54'37,21" S, 58°51'9,24" W, 6-xi-1999.
Description -Male: Idiosoma dorsally 721 long and 583 wide, ventrally 713 long. Dorsal shield complete, 300 long and 340 wide. Posterior to dorsal shield three irregularly shaped areas with a finer porosity.
Remarks -Male and female are well-described by Rosso de Ferradás (2006b) and therefore only some measurements are given and an illustration of the male dorsum is presented. The only difference with her illustration of the male is that the associated setae of Dgl-3 are located medially and distanced of these glandularia. The areas with finer porosity are not mentioned in the original description of K. Viets (1954b).
Remarks -According to Lundblad (1930), who examined the types of A. minimus (Daday, 1905) and A. rotundus (Daday, 1905), the two species can be separated based on the pair of glandularia anterior and posterior of the genital plates. In minimus the anterior pair is more separated than the posterior pair, in the rotundus it's the other way around. In my collection from Surinam, the Dadayella females show a large variation in the distance of these pairs of glandularia. In my opinion this characteristic is not suitable for species delimitation. The holotype of A. rotundus is lodged in the Naturhistorisches Museum in Basel, but unfortunately the slide does not contain the specimen (Hänggi pers. comm.). Daday's (1905) illustrations are too sketchy or even erroneous to draw any conclusions. K. Viets (1954b) came to the same conclusion as Lundblad (1930) about the glandularia anterior and posterior to the genital plates. According to Viets (1954b) the palp of A. minimus has P5 with a distinctly downturned claw and the ventral seta of P4 is without a hook, while the palp of A. rotundus has the claw of P5 more obliquely orientated and the ventral seta of P4 is with a hook. Based on these differences it is clear that my specimens from Surinam belong to A. rotundus. Rosso de Ferradas (1981a) reported A. nanus from Argentina, but according to Cramer & Cook (1992) the males must be assigned to A. rotundus. However, the males reported by Rosso de Ferradas (1981a) have a different configuration of the dorsal glandularia and setae (e.g. postocularia much closer to each other), differently shaped genital plates and antagonistic bristle without a hook, therefore they might belong to a different species. Unfortunately, I have not been able to examine these specimens.
gladiiferus doesn't belong to that species but to A. consanguineus. Arrenurus gladiiferus has a convex posterior margin of the cauda without an indentation, and the setae of P2 are gradually tapering and not sword-like as in A. consanguineus.
Distribution -Known from Brazil (Koenike 1894, Viets 1936, 1954a, Lundblad 1944) and Argentina (Rosso de Ferradas 1981b). Marshall (1903) reported this species from North America, but these specimens do not belong to A. corniger as the dagger-like petiole is lacking, the hump of the cauda is more pointed and the posterior end of cauda has a different shape.
Description -Male: Idiosoma brownish, dorsally 745 long and 429 wide; ventrally 788 long. Anterior idiosoma margin straight, posterolateral corners angular. Distance anterior idiosoma margin-dorsal shield 105, the latter 340 wide. Cx-I and Cx-II anterolaterally pointed. Cauda 373 wide, relatively long with a pointed hump, somewhat widened at level of hump, posteriorly truncated; posterior margin with a shallow indentation. Genital plates relatively short, 227 wide, swollen and visible as well in dorsal view.
Remarks -The male specimen of this study differs from the description of Rosso de Ferradas (1984) in the somewhat larger distance between the postocularia and the less truncated posterior margin of the cauda. However, it has similar angular posterolateral corners of the idiosoma, relatively short genital plates and the cauda with a pointed hump. Therefore, I assigned this specimen to A. deltensis. The female remains unknown.
Remarks -Arrenurus soesilae, known in the female sex only, is insufficiently described as the genital plates and the suture lines between the coxae are not illustrated. Nevertheless, based on the peculiar pointed posterior end of the idiosoma, it is clear that Makan (2005) illustrated the female of A. epimerosus. The female of the latter species is the only South American Arrenurus species known with such a pointed posterior idiosoma.
Distribution -Known from Brazil (Marshall 1919, K. Viets 1936, 1954a  Remarks -The slide with the syntype is partly dried, the type is squashed and positioned laterally. Only the cauda and part of the dorsal shield are well visible. Lundblad (1944) gave a very complete description of the species, and therefore only some measurements are given and some illustrations are presented. There is only one small difference with the description of Lundblad (1944) and the male specimen of the present paper in the configuration of the setae on the ventral side of the cauda. Lundblad illustrated the setae associated with Vgl-3 further posteriorly.  -leg-4-6: 146, 192, 190. Legs with numerous swimming setae.
Etymology -Named after the type locality, the Manso River.
Remarks -The new species is close to Arrenurus neuquenensis Rosso de Ferradás, 1987. The latter species is larger (842-909) and has a shorter and broader cauda, especially the part posterior to the humps of Lgl-4. Moreover, the idiosoma of the new species is more elongated compared to A. neuquenensis.
Remarks -The male is more or less similar to Arrenurus scopularis Lundblad, 1938, A. diversisetus K. Viets, 1940and A. neuquenensis Rosso de Ferradás, 1987. From A. scopularis the new species differs in a shorter dorsal shield. Moreover, Lgl-3 has shifted anteriorly and is lying close to the dorsal shield in A. scopularis, in the new species these glandularia are not visible in dorsal view. Arrenurus diversisetus has a smaller dorsal shield compared to the new species, and the dorsal cauda margin is undulating. Arrenurus neuquenensis has the cauda perpendicularly set off from the anterior idiosoma (obliquely in the new species), with lateral lobe-like extensions (without lobe-like extensions in the new species). The female doesn't match the description of other females with a patch of setae in P2 in the short and broad genital plates.
Diagnosis -Male: Anterior part of idiosoma wide, dorsal shield distanced from anterior idiosoma margin, with Dgl-2 and Dgl-3 close together. Cauda relatively short, with a rounded posterior margin. Female: Cx-IV without medial margin.
Remarks -The new species is most close to Arrenurus nitidus K. Viets, 1937 from Brazil, known from the male only. The latter species differs in a less wide anterior idiosoma (including the dorsal shield), a different configuration of the glandularia and associated setae of the dorsal shield (compare Figure 179 of K. Viets (1954a) with Figure 9A) and a straight posterior margin of the cauda. Unfortunately, Viets (1954a) Bolivia, 17°29.949 S 63°38.152 W, 10-iii-1999, leg. D. Tempelman (RMNH).
Diagnosis -Idiosoma anterlaterally with prominent, pointed humps, Dgl-1 on small humps, cauda laterally expanded, P2 with a patch of setae on a lateral extension.
Etymology -Named after David Tempelman (Amsterdam), collector of the material. Remark -The new species is similar to A. cornifrons Lundblad, 1938, but differs in that Arrenurus tempelmani has a more rounded anterior idiosoma, Dgl-1 lie on small humps (not on humps in A. cornifrons) and a more posteriorly widened cauda. Moreover, the setae associated with the Dgl-3 are located more posteriorly and the genital plates are more swollen compared to A. cornifrons.
Arrenurus tenuicollis acornutus K.O. Viets, 1968 Material examined -Argentina. Buenos Aires Province: 1/4/0, pond along Ruta 76, 2 km S of crossing with Ruta 86, 37°23'22,64" S, 61°0'14,81" W, 10-xii-1999. Remarks -The male specimen agrees well with the description of K.O. Viets (1968) in the large size, the anterior part of the idiosoma is distinctly set off from the idiosoma and IV-leg-4 has a short, rounded spur. The humps near the anterior idiosoma margin are a bit more pointed in the specimen from Argentina. An almost similar species, A. tenuicollis orthocercus Lundblad, 1944, is described from Brazil. The latter species has larger posterior extensions of the cauda and the anterior part of the idiosoma is not set off from the idiosoma. The female of this subspecies have not been described, but the females of this study are similar to the description given for A. tenuicollis orthocercus.Arrenurus tenuicollis K. Viets, 1936 is a highly variable species, thus far with six subspecies described. Whether these subspecies all belong to the nominate taxon should be examined by molecular studies.
Etymology -Named for its occurrence in lakes. Remarks -A difference with all known subspecies of Arrenurus tenuicollis is that Dgl-1 are not visible in dorsal view in the new subspecies. The male of A. tenuicollis tenuicollis K. Viets, 1936 has a small hump near the anterior idiosoma margin, a narrower, posteriorly more widened cauda compared to the new subspecies, A. tenuicollis megacercus K. Viets, 1954 and A. tenuicollis orthocercus both have the cauda with a posterolateral extension (absent in the new subspecies), additionally A. tenuicollis othocercus has IV-leg-4 with a spur, A. tenuicollis megaluroides Lundblad, 1944 has the idiosoma with lateral extensions (absent in the new subspecies) and near the anterior idiosoma margin there is a small to large, rounded to pointed hump (no hump in the new subspecies), A. tenuicollis gibberipalpis Lundblad, 1944 has a pointed hump near the anterior idiosoma margin (absent in the new subspecies), P2 with a large patch of setae (smaller in the new subspecies) and the accompanying setae of Dgl-3 are distanced from the glandularia (much closer to the glandularia in the new subspecies), A. tenuicollis acornutus has the anterior part of the idiosoma distinctly set off from the idiosoma (not set off in the new subspecies) and smaller genital plates, A. tenuicollis haitiensis Lundblad, 1944 has the idiosoma with small anterior humps, a more pointed dorsal shield, the postocularia are more distanced from Dgl-2 and P2 has a larger patch of setae. The female has been described for a number of subspecies, the known females have larger genital plates compared to the new subspecies. Only the A. tenuicollis gibberipalpis female has similar genital plates, but in this subspecies P2 has a much larger patch of setae.