Jaxea kuemeli Bachmayer , 1954 ( Malacostraca , Gebiidea , Laomediidae ) from the Middle Miocene of Tunjice Hills ( central Slovenia )

In the present paper we report on several new specimens of Jaxea kuemeli Bachmayer, 1954 from the Middle Miocene laminated sandstones from Košiše in Tunjice Hills. New and well-preserved material from shallow water environment of Laško Formation allows the re-evaluation of Jaxea cheliped morphology. The report enhances our knowledge of the variability of tooth formula in the cheliped of Jaxea kuemeli and opens questions about interspecific variations connected to temporal or ecological factors. We also discuss the environmental preferences of the species which is so far known exclusively from the Paratethys Sea.


Geological and stratigraphical settings
The area of the Tunjice Hills has been known for its wealth of fossil remains since the 19th century.In 1882 a well-known naturalists and local priest Simon Robič started collecting fossils and sent them to palaeontologists from the Natural History Museum in Vienna.Among these were also the first specimens of a brachyuran crab Cancer carniolicus Bittner, 1884, currently treated as Tasadia Müller in Janssen & Müller, 1984(Schweitzer et al. 2010).
Here presented specimens of Jaxea kuemeli were recovered from the Middle Miocene (Badenian) sandstones and sandy limestone exposed in a road cut along the local road from Kamnik to Tunjice some 3 km northwest of the town of Kamnik near the village of Košiše (fig.1).
The Tunjice Hills belong to the westernmost part of the Tunjice Syncline of the Sava Folds (Placer, 1999(Placer, , 2008)).In the south it borders with Triassic rocks of Trojane anticline and in the north to Teharje anticline and Menina mountain massif, both consisting of Triassic Dachstein limestone (Premru, 1983).The total thickness of the Miocene beds is estimated to approximately 1000 m (Žalohar & Zevnik, 2006).
The stratigraphic sequence of the Tunjice Hills starts with the Early Miocene (Burdigalian) Govce Formation.These strata consist of alternating conglomerates, sandstones, and finegrained marls, as well as clays with lenses of sand and sandstones.Sediments of the Govce Fm. were deposited in a near-shore environment with variable terrestrial and marine influence (Vrabec, 2000) with the total thickness of 350 to 450 m (Premru, 1983).Marine fauna retrieved from marls also indicates near-coastal environment with common wood remains drilled by teredinid bivalves, carbonized pine cones, and rich mollusc fauna (Žalohar & Zevnik, 1998).Remains of decapod crustaceans are rare in the Govce Fm. and so far the only finds are a handful of specimens of Retropluma slovenica Gašparič & Hyžný, 2014 from sandy beds of this formation (Gašparič & Križnar, 2017).

Material and methods
In total 30 specimens of Jaxea kuemeli from Košiše locality have been examined.Specimens were prepared using manual or pneumatic needle and studied under stereomicroscope Leica EZ4D.All specimens were measured, photographed using digital cameras Nikon Coolpix P340 and A900, and documented using computer graphic programmes (CoreDRAW X5, Adobe Photoshop CC).The material is deposited as a part of the "R.Gašparič Collection" in the Slovenian Museum of Natural History, Ljubljana, Slovenia (RGA/ SMNH).

Locality:
The specimens studied herein were recovered from grey to yellowish Middle Miocene (Langhian/Badenian) laminated sandstones of the Laško Formation exposed at the Košiše locality (Sava folds Basin, Slovenia).Laško Formation beds of this locality consist of grey siltstones with concretions, interbedded with laminated grey to yellowish sandstones, overlain by poorly sorted bioturbated yellowish sandstones and sandstones with Lithothamnium fragments.
Laminated sandstones are more likely to contain macrofaunal fossil remains, including decapods, than other variations in lithology.Remains of Jaxea kuemeli were collected exclusively from bedding planes of grey to yellowish laminated sandstones.

PLATE 1
Jaxea kuemeli Bachmayer, 1954.A-D RGA/SMNH 0704; A -cheliped with scattered remains of dorsal carapace and abdomen; B -close-up of abdomen with abdominal pleurae and fragmented telson; C -close-up of anterior part of dorsal carapace with rostrum; D -close-up of cheliped; E -RGA/SMNH 0743, isolated cheliped, exhibiting strong tooth on dactylus; F -RGA/SMNH 1193, chelipeds of fragmented specimen; G -RGA/SMNH 1099, propodus, with occlusal margin of fixed finger.All scale bars are 10 mm, except 1C scale bar is 5 mm.length, rounded, margins covered with minute spines, posterolateral margins concave.Telson longer than wide, posterior margin convex, dorsal surface with median longitudinal groove and two pairs of longitudinal ridges.Uropods equal in length to telson, with rounded posterior margin.Abdomen and telson weakly ornamented with small granules (Pl.1B).
First pereiopods chelate, marginally subequal, one chela more slender, other robust.Both chelae well developed and strongly calcified, equal in length to carapace and strongly granulated.Manus rectangular, slightly longer than high.Dactylus slightly longer than fixed finger.Occlusal margin of both fingers adorned with row of teeth.Fixed finger with three to five larger, rounded teeth positioned proximally in concave part of occlusal margin.These are followed by row several smaller teeth, gradually diminishing in size in distal half, here occlusal margin slightly convex (Pl.1G).Dactylus with two round teeth positioned proximally, first a small round tooth, followed by distinct strong tooth, knob like and proximally curved.Continuing distally follows a broad, unadorned notch and a large triangular median tooth (Pl.1E).Distal half of dactylus occlusal margin slightly concave and adorned with equally small rounded teeth as on fixed finger.Termination of both fingers curved together and pincers-like.Two longitudinal ridges on dactylus, one throughout the finger, second less distinct and only present in proximal half.Fixed finger with one longitudinal ridge through the whole finger length.Ridges as well as outside margins of fingers evenly ornamented with small, spine like teeth (Pl.1D).Pereiopods P2-5 simple, flattened and slender.
Remarks: Although Müller (1984bMüller ( , 1993Müller ( , 1998) ) and Mayoral et al. (1998) considered J. kuemeli to be possibly conspecific with extant species Jaxea nocturna Nardo, 1847, Hyžný (2011) argued for distinction between both taxa.Hyžný re-examined the type material of Bachmayer (1954) and additional specimens from Lower to Middle Miocene of Austria, Slovakia, and Hungary, and concluded that morphology of chelipeds expressed in unique tooth formula warrants keeping both species as separate.A major distinctive character is the position of the large median tooth on the occlusal margin of the fixed finger.In J. kuemeli this is located proximally relative to the position of the median tooth on the dactylus and less distinct, while it is positioned distally in J. nocturna and pronounced (Hyžný, 2011, p. 180, fig. 3).
Based on the cheliped morphology, the material from Košiše can be assigned to Jaxea kuemeli.The material confirms slight heterochely in the species as already documented (but not explored in detail) by Hyžný (2011).Additional intraspecific variation in the nature of the tooth formula is presented as well.Some specimens from Košiše do not show observable median tooth on the fixed finger or exhibits a different position of large proximal teeth on dactylus and constant rows of small rounded teeth in a distal half of fingers.These variations may be connected with temporal or ecological factors; more research, however, is needed to address these issues properly.
Taphonomy: Specimens of Jaxea kuemeli collected at the locality Košiše exhibit varying degrees of preservation.Only strongly mineralized chelipeds are commonly found due to the fragile cuticle of the dorsal carapace, abdomen, and pereiopods.Chelipeds are frequently found in pairs (Pl.1F) and, where carapace or abdomen remains are recognized, these are always associated with chelipeds (Pl.1A).Despite the fact that Jaxea representatives are active burrowers (Dworschak, 2004), described fossil remains are exclusively found on bedding plane and not in bioturbations present in the sediment.This type of preservation suggests limited post-mortem transport and rapid burial of remains, which likely represent moults rather than corpses (Glaessner, 1969).

Conclusions
A number of specimens of a laomediid shrimp Jaxea kuemeli are reported from the Middle Miocene beds of the Laško Formation exposed in the Tunjice Hills, central Slovenia.The species was a dominant decapod taxon of the studied infaunal community, in co-occurrence with a crab Tasadia carniolica.Intraspecific variation in the nature of chelipeds has been observed in the studied material of J. kuemeli.The intraspecific variation of cheliped in the fossil Jaxea has not been evaluated yet; with the increasing number of specimens of this species from various localities, such study is now feasible.Jaxea kuemeli has been identified in decapod associations of both shallow as well as deep water environments, which is in accordance with the ecological preferences of modern representatives of Jaxea.