Abstract
During the sampling campaign to describe the Iberian fauna of Collembola, an undescribed species of the family Bourletiellidae living on Genista hispanica L. was found with parasitic mites. The attached parasitic mites were identified as the larval instar of a new species of Polydiscia, a prostigmatid mite of the family Tanaupodidae Thor, 1935. The genus was previously cited in Austria. The Collembola, Deuterosminthurus bisetosus sp. nov, which was found in distant localities on the Iberian Peninsula, and Polydiscia deuterosminthurus sp. nov., are both here described. Both species were found together on Genista for three consecutive years. The abundant material obtained has allowed us to study both species with SEM (Scanning Electron Microscopy), and show characteristics in greater detail than has been possible with light microscopy.
Introduction
The Collembola are considered one the most abundant groups of Hexapoda as well as one of the most ancient, their systematics, taxonomy and ecology have been widely worked, but there still many species to describe and autoecological studies to be performed. Acari on Collembola have been reported in a few papers: trombidiid larvae on Entomobrya nivalis (L.) and Salina celebensis Schaeffer (Entomobryidae) (Handschin, 1926) , phoretic acarid and saproglyphid hypopi on Sminthurus fuscus (L.) (Sminthuridae) (Waldorf, 1974) , Erythrites sp. nr. womersleyi (Southcott, 1946) from two Australian species of the genus Corynephoria (Sminthuridae) (Greenslade & Southcott 1980) , and Cheyletus eruditus (Schr.) on unnamed Collembola in Poland (Haitlinger, 1991) .
ZOOTAXA
The genus Polydiscia was previously only known from a species, P. squamata (two specimens) captured by Methlagl (1928) in a locality close to Vienna (Austria). In this paper we describe a new species of this genus as parasite of a new species of collembolan with repeated and numerous captures. We can say with certainty that this species is a true ectoparasite of a Collembola. The abundance of specimens collected has allowed us to describe both species.
Materials and methods
The collembolan and mite specimens (Figures 1 and 2 ) were captured by beating the host plants (Genista hispanica L.) in the regressive plant communities of the Western Pyrenean and the Navarra-Alava series of Quercus humilis in Otazu (Navarra, Spain). Samples were taken in May of 1999 May of , 2000 May of and 2001 . The technique allowed us to capture other arthropods species at the same time. The presence of red coloured mites on the body of the new Collembola was detected in the field, but the parasitism was not confirmed until the sampled material was observed using a stereoscopic microscope in the laboratory. Some specimens were permanently mounted in Hoyer's medium on microscope slides. Species identification was carried out using a compound light microscope.
Materials and methods
Some specimens of both species were fixed and processed for scanning electron microscopy (SEM). The fixative consisted of a mixture of methanol, acetic acid and water 2:2:1 (Saito & Osakabe 1992) . After washing, samples were dehydrated through a series of increasing concentrations of ethanol up to 100%. Complete desiccation was achieved by the CO 2 critical point technique (CPD). Samples were then coated with a 16 nm layer of gold using a Emitech K550 sputter-coater and a 'DSM Zeiss 940 A' Scanning Electron Microscope was used for observation.
Materials and methods
For Polydiscia all measurements are in micrometers rounded to the nearest whole micrometer. Terminology follows that of Welbourn and Young (1987) . Legs were measured from the base of the trochanter to the base of the pretarsal claws.
Materials and methods
For Deuterosminthurus chaetotaxy terminology follows, with some modifications, Betsch & Bretfeld (1991) for abdomen and Nayrolles (1987) for tibiotarsi. For the head we follow de traditional denomination for Poduromorpha (Jordana et al, 1997) Legs (Figures 4 and 11-13 ). Femora of all legs divided; pretarsi I-III with a thin and curved sickle-shape empodium; paraxial and antiaxial smooth claws with similar shape, divided in two branches: paraxial branch longer, thinner and sharply curved; antiaxial branch foliate and sinuous. Legs I length 245 µm (229, 3) ; coxal field with 2 branched setae (2B); trochanter 1B; basifemur 1B; telofemur 5B; genu 4B, 3 σ 22 µm, 1 microseta κ 4 µm; tibia 9B, 4 φ 22 µm, 1 k 4 µm; tarsus 1 ω 27 µm, 1famulus ε 4 µm, 2 eupathidia with setules (ξh (= ST1 33 µm, pST1 13 µm) and ξp 22 µm) and 25 B. Legs II length 219 µm (218, (215) (216) (217) (218) (219) 3) : coxal field with 1 branched seta (1B); trochanter 1B; basifemur 2B; telofemur 5B; genu 4B, 1 σ 25 µm, 1 microseta κ 5 µm; tibia 9B, 2 φ 19 µm; tarsus 1 ω, 1famulus ε , 2 eupathidia with setules (ξh 29 µm, 7 µm and ξp 22 µm) and 21 B. Legs III length 245 µm (251, 245-259, 3); coxal field with 2 branched setae (2B); trochanter1B; basifemur 2B; telofemur 4B; genu 4B, 1 σ; tibia 9B, 1 φ; tarsus 20 B. PT= Paratype; LT= Lectotype; AM=anteromedial setae (trichobothridial); SS= posteromedial setae (trichobothridial); AL= anterolateral setae; PL= posterolateral setae; AA= distance between the insertion of setae AM; SB= distance between the insertion of setae S; AW= distance between the insertion of setae AL; PW= distance between the insertion of setae PL; ASB= distance between the anterior margin of the prodorsal sclerite and the base of botrichial setae S; PDB= distance between the posterior margin of the prodorsal sclerite and the base of botrichial setae S; SD=length of the prodorsal sclerite; SD= ASB+PSB; AP= distance between the insertion of setae AL and PL; pa=legI lengh; pm=leg II lengh; pp= leg III lengh; Ip=pa+pm+pp; T1-3= lenght of tarsus I, II and III. 
AM

ZOOTAXA
Discussion. We had the opportunity to study a lectotype of the type species (specimen also studied by Vercammen-Grandjean in his paper of 1972). However, it shows evidence of having been manipulated and actually lacks both pairs of trichobothria. Our observations expose errors of observation or interpretation of several characteristics given by Vercammen-Grandjean for the species. The missing setae enable us to confirm an important characteristic of this species and we were forced to follow Vercammen-Grandjean´s description and measurements of these setae.
ZOOTAXA
Although Vercammen-Grandjean (1972) indicate a palpalsetal formula for P. squamata of (B)-(B)-(N).N.N, the type studied shows a formula similar to that of P. deuterosminthurus sp. nov. and on the coxae, all the setae were described as nude (they are clearly branched setae). In leg I, P. squamata has two genualae σ and although VercammenGrandjean (1972) indicate two tibialae φ and 21 branched setae in the tarsus, the type specimen has four φ on tibia and 25B and ξp with setules in the tarsus.
ZOOTAXA
P. deuterosminthurus sp. nov. can be separated from P. squamata Methlagl, 1928 by the following characteristics: (1) besides length difference of the prodorsal sclerite (AD), AA, PW, AP (see table I), in P. deuterosminthurus sp. nov. setae PL>S>AL>AM versus PL<S>AL<AM. (Vercammen-Grandjean, 1972) in P. squamata; (2) shorter length of legs I-III in P. deuterosminthurus sp. nov., Ip = 710 (697, 3) versus Ip = 771 (742-800, 2) in P. squamata; (3) tarsus II shorter in P. deuterosminthurus sp. nov., T2 = 57 (56, 56-57, 3) versus T2 = 64 (63-64, 2) in P. squamata; (4) leg I with 3 σ in P. deuterosminthurus sp. nov. versus 2 σ in P. squamata.
ZOOTAXA
The specimens obtained by Methlagl of P. squamata were collected free-living in vacant lot and this species´s host is yet unknown.
ZOOTAXA
Biology. With the capture of the larvae of P. deuterosminthurus sp. nov. parasitizing D. bisetosus sp. nov., the first host association of this genus is established.
ZOOTAXA
Concerning the location of the mite on the host, the majority were found on the dorsal body surface, with the gnathosoma embedded in the posterior area of the articulation between head and prothorax (Figure 1 ). This location agrees with that seen by Greenslade & Southcott (1980) for the erythraeid parasites from Corynephoria observed in Australia.
ZOOTAXA
Although Greenslade & Southcott (1980) wrote that 'parasitism on the Collembola is unknown although animals seemed moved normally and on microscopic examination appear unaffected', we observe that the physiological effect on the host may be lethal since the infested hosts show a high degree of dehydration, with a lack of antennal turgescence in such a way that these appendices rest folded back. The mites are easily separated from the host and although light scars were observed, the degree of injury to the host cuticle was not great.
ZOOTAXA
When parasitic mite densities are high, the effect on collembolan populations could be significant (Greenslade & Southcott, 1980) . In our population the mean intensity of infestation is 1, although several Collembola bear two mites. The prevalence, that is, number of individuals of a host species infested divided by the number of hosts examined (Margolis 1982) , is around 10%. The relationship between parasite and host size is approximately 3:1.
ZOOTAXA
P. deuterosminthurus sp. nov. seems to have an annual cycle, with a larval parasitic instar during the spring. It shows a high specificity for the Collembola species later described, since the mite has been not found on other Collembola and arthropods living together with the parasite species.
ZOOTAXA
The sampling was extended over a period of several weeks after the first capture (May 1999). Adult specimens of the mites were never found. D. bisetosus sp. nov. and larvae of P. deuterosminthurus sp. nov. were not found on plants after the first fortnight of June, the moment of the year when temperatures increase and the environmental humidity does not allow the presence of Symphypleona on the vegetation. Material deposited: MZUN (Museum of Zoology, University of Navarra). Description (Figures 1, 14-42 ). Adults size. Female: 0.75-1.4 mm (n = 4); male: 0.85 mm (Figure 14) .
ZOOTAXA
Colour. Live specimens show a pale yellowish general appearance with brown-violet patches around the trichobothria insertions (A, B and C) as the most characteristic feature. They are variable from pale brown-violet to red patches over the great abdomen (Figures  36-42) . Specimens of this species collected from Pyrenees, Bardenas Reales (Southern Antennae (Figures 19-22 ). Antennal ratios: in female, ant. I/II/III/IV = 1/1.6/2.3/4.4 and antennal segment/cephalic diagonal = 1.7; in male, ant. I/II/III/IV = 1/1.5/2.8/6 and antennal segment/cephalic diagonal = 1.3. Male antennal segment II with acanthoids setae in three whorls: 2+2+3 and two more on antennal segment I. Additional posteroventral setae of antennal segment IV (ventral sensilla for some authors) on d3, d4 and d5 of male and female ( Figure 20, arrows) ; sensorial setae of male on d1 (0-1), d2-3 (1-2), d4, d5 and d6 (2); female: d2-d6 (2) (Figures 30-31 ). There are 11-12 whorls of structural setae. The antennal segments have a variable level of ringing in different specimens, higher in the male. Sensory organ of antennal segment III with three accessory sensillae, two long and one short. Figure 27 ), male; f: seta ventrolateral lightly swollen, posterior to lateral sensilla of female; g: second 'i' seta (contiguous to lateral sensilla 's') of male; h: lateral sensilla 's' of male; i: second 'i' seta (contiguous to lateral sensilla 's') of female; j: lateral sensilla 's' of female; k: trichobothria D of female; l: trichobothria E of female (Bar: 10 µm). 27. Chaetotaxy of great and small abdomen of male (nomenclature modified from Betsch & Bretfeld, 1991) . The hollow arrows points to the oval organs. 28. Chaetotaxy of great and small abdomen of female. The black arrow points to the setae drawn in 26f. The hollow arrows points to the oval organs. 29. Lateral colour pattern of a semi-pale specimen from Otazu (Navarra) (Bar: 10 µm) Head. Eyes: 8+8; eyepatch with two setae. Cephalic setae: mesochaetae, with setae closer to the eye and antennal insertion slowly thickened. Labral formula: 6/5-5-4. Ventral head-back with 1+1 oval organs (Figure 33 ). (abbreviations: c, cervical; v, vertical; o, ocular; d, dorsal; a, anterior; sd, sub-dorsal; g, genal; cp, clipeal posterior; cc, clipeal central; cm, clipeal medial; cma, clipeal medial anterior; ca, clipeal anterior; pl, pre-labral) . 34. Seta Sd'4 (black arrow in D) (Bar: 0.01 mm). 35. Female anal appendage (Bar: 10 µm) ZOOTAXA Furcula. Chaetotaxy as in Figure 32 . Length of the mucro: 50-65 µm (Figure 17) . Small abdomen. The males lack the a 2 seta on the first row of the small abdomen. There is a small sensilla just behind trichobothria E. Male genital papilla similar in size to ventral anal valves. Two oval organs on each side (hollow arrows in Figures 27-28) . Length of the anal appendages: 48 µm. (Figures 16 and 35) .
ZOOTAXA
Taxonomic discussion. The specific diagnostic characteristics of D. bisetosus sp. nov. are: two 'i' setae between 's' sensilla on lateral of the great abdomen and the fourth setae of row posterior to trichobothria C (Figures 27-28) (Bretfeld, personal communication) .
ZOOTAXA
N. apicalis can be distinguished from D. bisetosus sp. nov. because seta IIi is present only on leg III, the special ventral setae (sensillae for some authors) of the antennal segment IV are on d2, d4 and d5 segments, and four setae are present on retinaculum (Bretfeld & Arbea, 2000) .
ZOOTAXA
In the collection of the Museum of Zoology of the University of Navarra there is a specimen with asymmetry in the special ventral setae of the antennal IV (d2, d4, d5/d3, d4, d5) and with the terminal setae of the small abdomen of the male very similar to those of D. sulphureus.
ZOOTAXA
Specimens of other species have been compared with the new species: B. pallipes (Stach's collection, PAS), B. repanda Âgren, 1903 (Stach's collection, Szeptycki leg. and Weiner leg. specimens from PAS and six specimens from MHNG), B. mixta Gisin, 1957 and B. flava (holotype male and paratypes females from Vessi, Gisin collection, MHNG). All of these species have only an 'i' seta and a pattern of colouring different to those of the new species.

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