A redescription of the chigger Hannemania achalai Alzuet and Mauri, 1987 (Acariformes: Prostigmata: Leeuwenhoekiidae) in frogs from Sierra Grande, Cordoba, Argentina

We redescribe the endoparasitic chigger Hannemania achalai based on specimens collected from the type frog host (Pleurodema kriegi) and an additional host (P. cordobae) in the type locality of this mite (Pampa de Achala, Cordoba province, Argentina). Hannemania achalai is diagnosed by the following characters: palpal setal formula B/B/BBB/5B, palpal claw trifurcate, galeal seta B, parasubterminala I N, 2–4 genualae I, 1 genuala II–III, femorala III absent and coxa III with 1B. This redescription is accompanied by micrographs with scanning electronic microscopy and drawings.


Introduction
Chigger mites of the genus Hannemania Oudemans, 1911 (Acariformes: Prostigmata: Leeuwenhoekiidae) are temporary and highly specialized endoparasites of frogs, toads and salamanders (Amphibia). To date, 27 species are recognized, almost all from United States to Argentina, and only one from New Caledonia (Jacinto-Maldonado et al. 2016, Silva-de la Fuente et al. 2016. Chiggers are parasites only in larval stage and the taxonomy of this genus is entirely based on characteristics of this instar. Moreover, some species from South America are poorly described and in some cases the specific identification is not possible. The genus Hannemania is especially in need of revision. Hannemania achalai Alzuet and Mauri, 1987 was described parasitizing the frogs Pleurodema kriegi (Müller, 1926), Odontophrynus occidentalis (Berg, 1896), Pleurodema sp. and Odontophrynus sp. from Pampa de Achala, Córdoba, Argentina. Their brief original description lacks illustrations of idiosoma and legs, and details of leg and palp chaetotaxy.
The parasitic load by H. achalai in two frog species was analysed by Biolé et al. (2015). They found that P. kriegi has higher infestation by H. achalai than Pleurodema cordobae Valetti, Salas and Martino, 2009: prevalence (number of hosts infested with H. achalai divided by the number of hosts examined) 80.6% and 41.6%, mean intensity (average intensity of mites per infested frogs) 29.4 and 14.4, and the intensity range (minimum and maximum number of mites per infested frog in the sample) 1 -444 and 1 -49, respectively. The specimens examined by Biolé et al. (2015) for the analysis of infestation parameters are the same specimens examined here for taxonomic purposes.
In this paper, we give a redescription of H. achalai showing measurements, drawings and SEM micrographs of diagnostic morphological characters, based on specimens collected from the type host species P. kriegi and the additional host P. cordobae previously reported by Biolé et al. (2015), both collected in the type locality of the mite.

Materials and methods
Mites were extracted from subdermal layer of five specimens of P. cordobae and three specimens of P. kriegi, collected from the type locality of the mite species, and surroundings. The frog hosts are housed in the Colección Herpetológica, Ecología, Departamento de Ciencias Naturales, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Argentina. The collecting number of each frog inspected is indicated in brackets in material examined section.
Twenty-six mites randomly selected from each host specimen were cleared in lactophenol and mounted in Hoyer's medium. Drawings were made with a Nikon Optiphot 2 compound microscope (Tokyo, Japan) equipped with a camera lucida. Line drawings were edited using the GNU Image Manipulation Program (GIMP) (The GIMP team 2014). Six mite specimens were prepared for observing and illustrating with a Hitachi SU1510 scanning electron microscope (Tokyo, Japan), following the conventional SEM protocol provided by Alberti and Nuzzaci (1996).
All the mites obtained (n = 63), including those prepared for SEM (n = 6), mounted in microscope slides (n = 26) and specimens preserved in ethanol (n = 31) were examined for qualitative characters to carry out the redescription. Those preserved in ethanol were previously and temporally mounted in a drop of lactic acid on cavity slides. Nomenclature of measured morphological structures follow Goff et al. (1982) and Stekolnikov (2013), all measurements are in micrometers (μm) and were taken from 26 specimens preserved in Hoyer's medium. All the mite specimens analysed are deposited in the Colección Nacional de Ácaros (CNAC) kept at the Instituto de Biología, Universidad Nacional Autónoma de México in Mexico City, Mexico.
Material examined -6 larvae (CNAC007184-007187) ex Pleurodema cordobae [847], ARGENTINA, Córdoba, Los Linderos, -32°01'04.9", -64°56'22.9", 2621 m a.s.l., 15 Dec. formula, the palpal claw, and the number of specialized nude setae on legs: genualae I-III,  tibialae I-III, tarsalae and pretarsalae I-II, and subterminala I. However, the specimens analysed in this study differ from the original description by Alzuet and Mauri (1987) in the following characters: 1) the shape of galeala which is sparsely branched instead nude as mentioned by Alzuet and Mauri (1987), and 2) the presence of 2 genualae I constantly, whereas in the type specimens the number of genualae I range 2-4 (Alzuet and Mauri 1987). These differences are considered here as intraspecific variation until type material can be examined.
According to Alzuet and Mauri (1987) and Salazar Martínez et al. (2004) the type material is deposited at Museo de La Plata (MLP), Argentina, however, types were not seen for this study.