Oribatid mite fossils from pre-Quaternary sediments in Slovenian caves III. Two new species of Dissorhina (Oppiidae) from the Pliocene

Two new fossil species of the extant genus Dissorhina Hull, 1916 (Oribatida, Oppiidae) are described from Pliocene clastic sediments in Trhlovca cave of the Slovenian Classical Karst (Kras): Dissorhina paleokrasica n. sp. and Dissorhina nuda n. sp.. Diagnoses of both new species are given on the basis of detailed study of few damaged adult individuals obtained by sieving. Relationships to recent species of the genus and the possible importance of the Balkan Peninsula for the speciation of Dissorhina are discussed.


INTRODUCTION
The presence of oribatid fossils in Pleistocene and early Pliocene cave sediments of Slovenian Classical Karst, first reported by Moldovan et al. (2011), represents until now a rather unique record of oribatid fauna of these periods. The first paper of this series (Miko et al., 2012) dealt with two new species and genera of Oppioidea and presented a short overview of known oribatid fossils. The next paper dealt with the description of a new species of the newly established genus Amiracarus (Microzetidae), found in several fossil profiles of Slovenian caves (Miko et al. 2013). The present paper represents the last part of this series in which descriptions of two new fossil species of the extant genus Dissorhina Hull, 1916 are given. These species, found in upper and lower Pliocene sediments of Trhlovca cave (Slovenian Classical Karst), were reported for the first time by Moldovan et al. (2011) as Dissorhina sp. and Rhinoppia sp..

MATERIALS AND METHODS
All fossils of Dissorhina described here were collected by Oana Moldovan, Andrej Mihevc and Ioana Meleg from sediments in Trhlovca cave, Slovenia (45°40'18,8"N;13°56'45"E). Details about the location of findings and age of relevant sediments are given for each individual within description of species in the section "Material examined".
For extraction of fossil oribatid material, approximately 1 kg of sediment was removed and placed in sealed, labelled plastic bags. In the laboratory, the sample was immersed in 10 % KOH for 30 min, and then washed successively through sieves of 250 µm, 125 µm and 40 µm aperture sizes. Sub-samples Miko L. for each sieve dimension were examined separately under an Olympus SZX2 stereomicroscope in 90°alcohol and mites were removed.
All specimens were studied and documented by drawings in open cavity-slide preparations with lactic acid as a medium under a compound light microscope equipped with camera lucida. Given the poor state of the specimens and the limited number of individuals, SEM photography was not attempted.
Light microscope photos were taken by Jan Mourek (Prague, Czech Republic) and by Oana Moldovan (Cluj-Napoca, Romania).
Measurements of all individuals were made as in previous works (see Miko et al., 2012;Miko et al., 2013 for details). All measures are given in µm. For morphological terminology and meaning of setal formulas see Miko (2006).
Measurements -Available specimens partly crushed, not allowing precise measurements. Body length of holotype about 300 µm, length of prodorsum about 100 µm, maximum notogaster width about 150 µm (actual values for damaged specimen).
General characters -Original colour difficult to estimate, available fossil material pale, yellowish brown, partly covered with debris and dirt, making observation of finer structure difficult. Cuticle smooth as far as possible to observe, prodorsum laterally with granular microstructure.
Prodorsum -Prodorsum relatively narrow, delicate. Rostrum with two incisions as usual for Dis-sorhina, central tooth broadly pentagonal, blunt anteriorly, bearing a pair of rostral setae, inserted close to each other. Lateral teeth of rostrum short, broad, with blunt, rounded tips. Pedotectum I weakly developed as triangular projection with rounded tip, only slightly projecting over prodorsal outline. Another blunt projection visible on the place of pedotectum II. Only proximal part of lamellar costulae developed (i.e. reaching from bothridium to prodorsal groove and not beyond), costulae finely developed, oblique, straight or only slightly bent. Bothridia relatively small, rounded, with no or only indistinct posterior lobe. Postbothridial tubercle separated from bothridia, developed as small round tubercle. Interbothridial tubercles rather small and fine, not fused with anterior border of notogaster, their mutual distance same or smaller than distance between them and bothridia. Longitudinal, laterally rounded and flat "ear-like" carina developed in lateral part of prodorsum, above insertion of leg II. Sensillus moderately long (65 -70 µm), lanceiform, smooth, stalk about one half of the length or slightly longer, lanceiform head about 2,5 times broader than stalk. Prodorsal setae of different lengths and forms. Rostral setae rather fine, slightly bent or straight, smooth or with one bristle, about 27 µm long. Lamellar setae shortest, fine, straight, about 15 µm long. Interlamellar setae stronger, straight, slightly over 30 µm long with about 5-6 small bristles unilaterally, better visible in lateral view. Exobothridial setae not observed, their insertions nevertheless positioned on small tubercles. Another small tubercle may be present in close vicinity to them.
Legs -One of the two individuals (holotype) was relatively well preserved, with almost all legs present, even if incomplete. Due to the risk of fur-ther destruction, only leg I was investigated. As far as possible to observe, leg setation formula corresponds to those of Dissorhina as usual i.e. setation of leg I: 1-5-2(1)-4(2)-20(2). Setae moderately long, at least some of them with several short bristles. Tarsal solenidia ω 1 and ω 2 of about same length, ω 1 blunt and bent towards the tarsal surface. Tibial solenidion ϕ 1 setiform, longer than the length of tibia. Solenidion ϕ 2 much shorter, blunt. Genual solenidion σ long, setiform, more than two times longer than the length of the segment. of years old; see Moldovan et al., 2011 for further details) was much better preserved, and is designed as holotype. Individual (paratype) from sample T2 from Pliocene beige clay sediments (about 2,7 million years old) was damaged, in poor condition, without legs and practically without observable setation. Notogaster was largely damaged and dirty, not allowing more detailed study. Specific identity of the two individuals is judged on the basis of the same development of the rostrum, bothridia and lamellar costula, interbothridial and postbohridial tubercles and lateral part of prodorsum, and due to its occurrence in the same locality. Individuals are preserved in the collection of Emil Racovita Institute of Speleology in Cluj-Napoca, Romania.
Derivatio nominis -The name "paleokrasica" is derived from "Kras", the name of the Slovenian geomorphological unit where is the type locality, Trhlovca cave. Prefix paleo-refers to the fossil character of the material.
Remarks -Dissorhina paleokrasica n. sp. bears all important characters of the genus, and is close to the widely distributed and common species D. ornata. Our own studies showed that several characters of D. ornata may be rather variable (see also figures in Miko, 2006), so differences of the newly described fossil species needed to be carefully analysed against that variability. However, the newly described species can be distinguished from all other Dissorhina species by a combination of some specific characters, namely: (a) interbothridial tubercles are fine, weakly developed and not fused with anterior margin of noto- gaster (developed as separate tubercles); (b) anterior part of notogaster between setae c2 is arched and protruding anteriad; (c) central tooth of rostrum is broad, bluntly pentagonal or almost quadrangular, not trapezoid as in D. ornata or some other species; (d) notogastral setae except c2 and p1-p3 are quite long, and at least la, lp and h2 with small bristles.

Dissorhina nuda n. sp. (Figures 3A-E and 5A-C)
Diagnosis -Dissorhina with prolonged central tooth of the rostrum and prodorsum without lamellar costulae. Interbothridial sclerites near to each other, small, touching the anterior border of notogaster, but not fully fused with it. Insertions of interlamellar setae shifted backwards, near anterior margin of notogaster, laterally to interbothridial sclerites. vation of finer structure difficult. Cuticle smooth as far as possible to observe.

Measurements
Prodorsum -Triangular, shaped as usual in Dissorhina. Rostrum with elongated "naso"-like central tooth, protruding significantly beyond the anterior margin of rostral tectum. Lateral teeth reduced, broadly rounded. Pedotectum I present but weakly developed, protruding anteriad as a small rounded projection. Projection in the place of pedotectum II also present, but invisible in dorsal view. Costulae completely reduced, central part of prodorsum without visible cuticular structures, ridges or furrows. Postbothridial tubercles present, disctinct, and as usual for Notogaster -Broadly ovate, anterior border arched, without projections. Only some insertions of setae observable, insertions of both c2 setae, left la, right lm, left h1 and h3 and both p3 not observed. Single seta la preserved on right side, rather short (18 µm), smooth, without visible bristles. Other characters of notogaster very hard to detect.
Ventral characters -Infracapitulum and anal plates missing. Small but distinct pedotectum I and II visible. Epimeral area laterally with coarse granulation. Epimeral setation incomplete, even insertions not all visible. Nevertheless, epimeral setal formula can be reconstructed as 3-1-3-3. Only three epimeral setae preserved, smooth and fine, of different length (1a 11 µm, 4b 17 µm long). Anal opening visibly larger than genital opening, distance between them about as long as anal opening. Anal plates missing, and only incomplete set of setae and/or their insertions can be observed in anogeni-tal region, anogenital formula except anal setae may be reconstructed as 5g, 1ag, 3ad. Adanal setae ad3 longest of all ventral setae (about 22 µm), aggenital setae only slightly shorter. Insertions of setae p1 and p2 also visible in ventral view, close to each other.
Legs -Only trochanters of legs III and IV preserved, setation or insertions of setae invisible.
Material examined -Single damaged individual (holotype) was available from the clastic sediments of Trhlovca cave in Karst, Slovenia, sample T2 from Pliocene beige clay sediments (about 2,7 million years old). Individual is preserved in the collection of Emil Racovita Institute of Speleology in Cluj-Napoca, Romania.
Derivatio nominis -The specific name "nuda" reflects the absence of costular structures on prodorsum.
Remarks -This species, due to the absence of prodorsal structures, was originally determined and recorded as Oppiella (Rhinoppia) sp., potentially a new undescribed species (see Moldovan et al., 2011). However, the position of the rostral setae, shape of sensillus, presence of isolated postbothridial tubercles not attached to bothridium and 5 genital setae place this species clearly within Dissorhina. The trend of the disappearance of prodorsal costulae and prodorsal furrow is common within Oppiellinae, and can be observed also in recent Dissorhina species, e.g. D. tricarinatoides (Dubinina, 1966). The new species can be easily distinguished from all known species of the genus by the unique shape of the interbothridial tubercles, combined with the absence of lamellar costulae and peculiar shape of the central tooth of the rostrum.

DISCUSSION
Genus Dissorhina is widely distributed in Europe, mostly represented by common species D. ornata (Oudemans, 1900). Other European species with broader distribution are D. tricarinatoides (Dubinina, 1966) andD. signata (Schwalbe, 1989). While species richness of this genus seems to be limited in large parts of the continent, several other species were described from south-east part of Europe, mostly from Balkan Peninsula (Kunst, 1958;Mahunka, 1974;Mahunka, 2006;Mahunka, 2007;Mahunka et Mahunka-Papp, 2008). This may indicate the importance of this area as a possible centre of speciation of Dissorhina. The finding of two more species of this genus in sediments of Tertiary age from this area supports this hypothesis