New records of the genus Limnohalacarus ( Halacaridae , Trombidiformes ) from southern Brazil

Two Limnohalacarus species are reported from the southern Brazilian state of Rio Grande do Sul, Limnohalacarus cultellatus Viets, 1940 and L. mamillatus Fain & Lambrechts, 1987, originally described on the basis of individuals from the Caribbean region and aquaria in Belgium, respectively. The former species is also known from Madagascar, Hungary, North America, and was referred to Brazil and El Salvador in the literature. The latter species is also known from Western Australia.

The fresh to slightly brackish water mites of the genus Limnohalacarus have a worldwide distribution.Its individuals often catch the attention during the sorting of meiobenthic samples due the usual presence of an ovoid body of excreted material and by the fact that females keep eggs attached to their hind legs until hatching.
According to Bartsch (2013a), the genus Limnohalacarus comprises 13 valid species: L. africanus Walter, 1935, L. australis Bartsch, 1999, L. capernaumi Petrova, 1966, L. cultellatus Viets, 1940, L. dentatus Bartsch, 2013, L. fontinalis Walter & Bader, 1952, L. inopinatus Fain & Lambrechts, 1987, L. lanae Green, 1976, L. major Bader, 1968, L. mamillatus Fain & Lambrechts, 1987, L. novus Bartsch, 2013, L. portmanni Bader, 1967, and L. wackeri (Walter, 1914).The genus is characterized by the sharing of the absence of the third pair of dorsal setae; the first pair of gland pores anteriorly placed; fourth and fifth pairs of gland pores on the striated cuticle lateral to posterior dorsal plate; genital acetabula arranged along lateral margins of genital plate (or region, with ventral plates merged into a ventral shield), including several acetabula anterior to the level of genital opening; anal sclerites very small; palps four-segmented, attached dorsally; apical pair of maxillary setae in dorsal position; second palpal segment with short basal spur and long distal seta, third with large ventral spine, and fourth with six setae and a spine; tarsi I to IV with pair of basal lamellae which may be fused to a ventral knob, tarsi with 1,0,0,0 ventral, 3, 3, 4, 3 dorsal setae; Paired claws of tarsi with pectines with arrangement and size of tines on claw I different from those on posterior tarsi.
Thus far, a single species was reported in the Neotropical region, L. cultellatus.Published records in America range from northern USA to the Caribbean region (Viets 1940;Bartsch 1984Bartsch , 2011)).According to Bartsch (2011) there are unpublished records from Central-West Region of Brazil (Mato Grosso State).The present article extends the range of L. cultellatus further south to Rio Grande do Sul and reports another species, L. mamillatus.Occurrences of both species are summarized in Figure 1.
The specimens were collected from floating aquatic plants on Imbé Lake (29°57'30.63"S, 50°09'14.50"W) (Imbé, Rio Grande do Sul, south Brazil).In fact, this "lake" drains to the sea and has a salinity gradient that ranges from brackish to freshwater.The companying fauna from the place where Limnohalacarus individuals were found, however, included only freshwater taxa, with representatives of the Hydrachnidia, genus Arrenu rus Dugès, 1834, for example.
For the descriptions presented below, individuals were sorted under a stereoscopic microscope and were fixed in 70% alcohol.The diagnoses were based both on the specimens here described and data from literature (Bartsch, 2013a), including measurements.The mites were cleared in lactic acid and mounted in glycerin jelly.Individuals are deposited in the Acarological collection of the Universidade Federal de Minas Gerais (UFMG-AC).The illustrations were made with the aid of a drawing tube connected to a Leica DM2500 phase contrast microscope.The plates were prepared using Adobe Illustrator CS5.1.
Limnohalacarus mamillatus may be set apart from all those species for bearing 9 setae on tibia I. Bartsch (1999) described the species L. billabongis as a distinct species based upon specimens from the Northern Territory, Australia due differences in exoskeleton ornamentation (only marginal areas of PE and lateral portions of PD have a reticulate ornamentation according L. mamillatus original description, instead the entire plate as L. billabongis).Further minor differences regards their length:width ratios, the position of the basal seta on P-2, and the size of the dorsal pair of maxillary setae.In her revision of the genus Limnohalacarus, Bartsch (2013a) regarded all these differences as negligible, and L. billabongis as a junior synonym of L. mamillatus, something we follow here.
Concerning the above mentioned minor differences, Brazilian specimens are in complete agreement with the material described by Bartsch (1999) from Australia.Only the number of pgs is variable, with one or two pairs on genital sclerites of Brazilian material instead of a single pair of such setae in Australian individuals.Viets, 1940 Figures 1 and 4 Diagnosis.Female: Length 272-325 µm.Dorsal plates reticulated, except for smooth anteriormost part of AD.Medial and lateral eye pigment absent.Length:width ratio of AD 1.0-1.2.OC divided, with narrow triangular sclerite bearing gland pore.PD 1.5-2.1 times longer than wide and 2.5 times longer than AD.Second pair of dorsal setae present.Ventral plates separated.GP with 4-9 pairs of gac, three, rarely four pairs of pgs and two pairs of sgs.Gnathosoma 1.3-1.5 times longer than wide; rostrum slender.Both pairs of maxillary setae slender.Pharyngeal plate removed from margin of gnathosomal base by more than half its length.P-2 basally abruptly widened, in lateral aspect rectangular and with straight dorsal margin.Telofemur I 1.6-1.8times longer than wide.Tarsi with spiniform lamellae near their bases.Trochanters I to IV with 1, 1, 1, 1 setae, basifemora with 4, 3, 2, 1 setae, genu III with four setae, and tibiae I to IV with 7, 6, 7, 6 setae.On tibiae I to III 1, 1, 2 of setae pectinate, on tibia IV all setae slender.Tibiae III and IV with four and three ventral setae, respectively.All tarsi with pairs of pas singlets.Claws on tarsus I slender, claws with lamellar basal process and delicate apical tines.Claws of tarsi II to IV with series of crest (a raised area on anterior AD) and the first pair of dorsal setae being apart from the anterior margin of anterior dorsal plate.Both features, however, could be observed in Brazilian material.In the original description, Viets (1940) depicted the anterior strip of smooth cuticle on AD in his Figure 5 and mentioned the "crest" as a domed area bearing pair of ds-1 ("...hat das Praedorsale vorn in der Mitte keine Spitze neben den beiden dort stehenden Härchen, sondern nur eine sanfte Vorwölbung seines Vorderrandes").

ACKNOWLEDGMENTS
Special thanks are due to Dr. Norma Luiza Würdig and Dr. Carla Penna Ozorio for their kind support during first author's field work activities at CECLIMAR-UFRG (Centro de Estudos Costeiros, Limnológicos e Marinhos da Universidade Federal do Rio Grande do Sul).This article was supported by FAPEMIG 01/11 CRA APQ 00543/11 ("Taxonomia de ácaros Prostigmata, com especial atenção à família Halacaridae") and CAPES (Programa de Apoio à Pós-Graduação, IBUSP).Thanks are also due to Dr. Ilse Bartsch (Forschungsinstitut Senckenberg) who kindly sent copies of some articles that were lacking in our libraries.We also thank the reviewers and Check List editor Dr. Regiane Saturnino for their contributions to the manuscript.