Complementary description of Podocinella misella (Berlese, 1913) (Acari: Podocinidae) and a key to world species of the genus

Podocinidae Berlese is known in South America from only one species described from Brazil and several other locations on the continent. A complementary description of Podocinella misella (Berlese) is presented based on the morphology of adult females from litter collected in different parts of Brazil. Complementary characterization of the genus and a key to distinguish the five recognizable world Podocinella species are also presented.


Introduction
Podocinidae sensu Lindquist et al. (2009) is a small family of mesostigmatic mites, comprising only two genera: Podocinum Berlese, 1882, with thirty-one species, and Podocinella Evans & Hyatt, 1958, with five species (Yan et al., 2012;Santos et al., 2017). Podocinidae has also been used by other authors to comprise a different set of taxa, as discussed by Sourassou et al. (2015).
Podocinids are frequently found in litter samples in Brazil (Mineiro & Moraes, 2001). In a recent publication, we reviewed the species of Podocinum occurring in the country, describing a new species (Santos et al., 2017). The objective of this paper is to provide morphological information about specimens of Brazilian populations identified as Podocinella misella (Berlese, 1913), revise the concept of Podocinella as to integrate additional morphological attributes observed in this study, and finally to present a key to world species of the genus.

Material and methods
Mites were extracted from litter samples using a Berlese funnel. They were then slide-mounted in Hoyer's medium and examined under phase (Leica, DMLB) and interference (Nikon, Eclipse 80i) contrast microscopes for species identification, using the world taxonomic literature (Ho & Wang, 2009). In addition to the specimens collected during this work, we also examined specimens of the same species previously collected by other people and deposited in the reference collection of Departamento de Entomologia e Acarologia, Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo, Piracicaba, São Paulo.
Photos of taxonomically relevant structures were taken using a digital camera connected to the interference contrast microscope. Illustrations were produced using a digital tablet and the software Adobe Illustrator®. Measurements were done with a graded ocular. For each character, the average measurement followed (in parentheses) by the minimum and the maximum measurements are given in micrometers. Setal nomenclature is based on Lindquist & Evans (1965) and Lindquist (1994) as interpreted for the Podocinidae by Yan et al. (2012). However, that assignment is tentative, pending adequate ontogenetical study of this mite group, as for example done for Zerconidae by Lindquist & Moraza (1999). Nomenclature of opisthogastric setae is different from what was proposed by Santos et al. (2017) and in accordance with what was used by Lindquist & Moraza (1999), to better match what was reported in the latter publication as well as in other publications concerning the ontogenetic development of mesostigmatid mites. Leg setal notation and chaetotactic formulae are based on Evans (1963).
The key to species was constructed taking into account the original descriptions of all species, as well as the redescription of Podocinella misella (Berlese) by Evans & Hyatt (1958) and the examination of specimens of this species collected in Brazil.
A comparison of the specimens collected with type specimens of P. misella was not possible, because the type specimens could not be located; according Castagnoli & Pegazzano (1985) the types are missing. Evans & Hyatt (1958) provided a complementary description of this species based on specimens collected in Tomohon, Sulawesi (mentioned as N.E. Celebes), Indonesia and Jamaica. Hurlbutt (1972) presented a new complementary description based on specimens collected from Morogoro river (Tanzania) and reviewed the specimens used by Evans & Hyatt (1958) collected in Celebes.
The specimens that we examined from Brazil agree well with the redescription of Podocinella misella by Hurlbutt (1972). While his description was rather detailed, it included no setal measurements, leg chaetotaxy or details of the hypostome. Despite the missing information, we concluded that the specimens we collected belong to P. misella, because other features are sufficiently detailed, in addition to the fact that approximate setal length can be inferred from the illustrations provided and that setations of femur, genu and tibia (most variable segments between species) are provided.
Peritreme and peritrematic plate -Peritreme about as wide as stigma, usually extending forward beyond level of j1.
Spermathecal apparatus -Indistinct. Legs -Leg I much longer than legs II-IV, antenna-like, terminating in a whip-like seta, without pretarsi. Legs II-IV with median section of pulvilli rounded, paradactyli elongate and acuminate.
Remarks -The indistinct sperm access system in Podocinella and the apparent absence of males in this genus lead to the assumption that species of this genus could reproduce by thelytoky. This type of parthenogenesis has been proven by Wong (1967) for Podocinum pacificum.