Dissorhina paleokrasica, Miko, 2015

Miko, L., 2015, Oribatid mite fossils from pre-Quaternary sediments in Slovenian caves III. Two new species of Dissorhina (Oppiidae) from the Pliocene, Acarologia 55 (4), pp. 449-457 : 450-452

Dissorhina paleokrasica n. sp.

( Figures 1 A-C, 2A-E, 4A-G, and 5D-E)

Diagnosis — Dissorhina (see Miko, 2006) with broadly pentagonal rostrum, fine and rather straight lamellar costula. Interbothridial tubercles small and not fused with anterior border of notogaster. Notogaster in axial part protruding anteriad and notogastral as well as interlamellar setae with about 3-5 bristles unilaterally.

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 Dissorhina , 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.

Notogaster — Broadly oval in shape, with anterior border protruding anteriad, darker in transmitted light. Notogastral crista present, short, bearing short setae c1. Other notogastral setae longer, fine, attenuated towards the end, adhering to the surface. Setae h1 inserted closely to each other, distally divergent. Not all setae observable on available material, but at least setae la, lp, h2 and h3 with about 3-4 fine bristles unilaterally. Setae h1 and p1 smooth, without bristles. Approximate length of setae la 21 µm, lp 29 µm, h1 and h2 32 µm and p1 19 µm.

Ventral characters — Infracapitulum as usual in Dissorhina , setae of infracapitulum and palps fine and smooth. Epimeral setation 3-1-3-3, epimeral setae straight, smooth, about 11 – 12 µm long, 1c and 3c and 4b-c being the longest. Trochanteral setae I and II very long, bent, with few short bristles. Epimeral area with several lighter maculae in central part. Discidium developed as small, blunt tubercle. Anogenital formula as usual (5g, 1ag, 2an, 3ad), setae smooth and narrow, mostly a bit longer than epimeral ones (g1 8 µm, g6 13 µm, ag 14 µm, an2 15 µm). Adanal setae longer, ad1 posterior, ad3 anterior to anal opening.

Legs — One of the two individuals (holotype) was relatively well preserved, with almost all legs present, even if incomplete. Due to the risk of further 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 ’ 1 setiform, longer than the length of tibia. Solenidion ’ 2 much shorter, blunt. Genual solenidion σ long, setiform, more than two times longer than the length of the segment.

Material examined — Two individuals were available from the clastic sediments of Trhlovca cave in Karst, Slovenia. Individual from sample T5 from Pliocene red clay sediments (about 3,8 millions

Miko L.

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 notogaster (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.

Figures

FIGURE 1: Dissorhina paleokrasica n. sp.: A – dorsal view of holotype; B – dorsal view of paratype; C – detail of the prodorsum of paratype. Scale bar: A, B – 100 µm, C – 50 µm. Acronyms: bo – bothridium, cos – lamellar costula, ctr – central tooth of rostrum, ibt – interbothridial tubercle, lc – lateral carina, ltr – lateral tooth of rostrum, pbt – postbothridial tubercle, pt I – pedotectum I, pt II – pedotectum II, ss – sensillus. Setae are labeled by name.