Dissorhina nuda, 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 : 453-456

Dissorhina nuda n. sp.

( Figures 3 A-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.

Measurements — Damaged individual does not allow precise measurement, the values therefore represent actual values at damaged individual. Length of the body about 325 µm, length of the prodorsum about 105 µm. Maximum width of notogaster about 180 µm.

General characters — Original colour difficult to judge, available 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 — 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 Dissorhina not fused with posterior end of bothridia. Interbothridial tubercles small, fine, positioned near to each other. These tubercles posteriorly not fused with but only touching anterior border of notogaster. Prodorsal setae missing on observed individual. Insertions of rostral setae positioned on the base of central tooth of rostrum. Positions of lamellar setae impossible to observe, insertions of interlamellar setae positioned close to the anterior border of notogaster, laterally to interbothridial sclerites. Insertions of exobothridial setae on small, but distinct tubercle, as usual in Dissorhina . Sensillus quite long (about 70 µm), with narrow elongated head of typical Dissorhina shape.

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 anogenital 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.

Figures

FIGURE 3: Dissorhina nuda n. sp.: A – dorsal view of holotype; B – ventral view of holotype; C – detail of rostrum, dorsal view; D – bothridial area with sensillus; E – detail of rostrum, lateral view. Scale bar: A,B – 100 µm, D – 50 µm. Acronyms: bo – bothridium, ctr – central tooth of rostrum, ibt – interbothridial tubercle, ltr – lateral tooth of rostrum, pbt – postbothridial tubercle, pt I – pedotectum I, pt II – pedotectum II, ss – sensillus, tr III – trochanter of leg III, tr IV – trochanter of leg IV. Setae (or their insertions) are labelled by name.